| Doc. no. | N2950=09-0140 |
| Date: | 2009-09-27 |
| Project: | Programming Language C++ |
| Reply to: | Howard Hinnant <howard.hinnant@gmail.com> |
Reference ISO/IEC IS 14882:2003(E)
Also see:
This document contains only library issues which have been closed by the Library Working Group as duplicates or not defects. That is, issues which have a status of Dup or NAD. See the Library Active Issues List active issues and more information. See the Library Defect Reports List for issues considered defects. The introductory material in that document also applies to this document.
Section: D.9.1.3 [auto.ptr.conv] Status: NAD Submitter: Nathan Myers Opened: 1997-12-04 Last modified: 2006-12-29
View all issues with NAD status.
Discussion:
Paragraph 1 in "Effects", says "Calls p->release()" where it clearly must be "Calls p.release()". (As it is, it seems to require using auto_ptr<>::operator-> to refer to X::release, assuming that exists.)
Proposed resolution:
Change 20.6.4.3 [meta.unary.prop] paragraph 1 Effects from "Calls p->release()" to "Calls p.release()".
Rationale:
Not a defect: the proposed change is already found in the standard. [Originally classified as a defect, later reclassified.]
Section: 21.4 [basic.string] Status: NAD Submitter: Beman Dawes Opened: 1997-11-16 Last modified: 2006-12-27
View all other issues in [basic.string].
View all issues with NAD status.
Discussion:
In Morristown we changed the size_type and difference_type typedefs for all the other containers to implementation defined with a reference to 23.2 [container.requirements]. This should probably also have been done for strings.
Rationale:
Not a defect. [Originally classified as a defect, later reclassified.] basic_string, unlike the other standard library template containers, is severely constrained by its use of char_traits. Those types are dictated by the traits class, and are far from implementation defined.
Section: 27.5.3 [fpos] Status: NAD Submitter: Matt Austern Opened: 1997-12-15 Last modified: 2006-12-27
View all other issues in [fpos].
View all issues with NAD status.
Discussion:
Table 88, in I/O, is too strict; it's unimplementable on systems where a file position isn't just an offset. It also never says just what fpos<> is really supposed to be. [Here's my summary, which Jerry agrees is more or less accurate. "I think I now know what the class really is, at this point: it's a magic cookie that encapsulates an mbstate_t and a file position (possibly represented as an fpos_t), it has syntactic support for pointer-like arithmetic, and implementors are required to have real, not just syntactic, support for arithmetic." This isn't standardese, of course.]
Rationale:
Not a defect. The LWG believes that the Standard is already clear, and that the above summary is what the Standard in effect says.
Section: 22.4.1.5 [locale.codecvt.byname] Status: Dup Submitter: Matt Austern Opened: 1998-01-14 Last modified: 2006-12-30
View all other issues in [locale.codecvt.byname].
View all issues with Dup status.
Duplicate of: 19
Discussion:
Section 22.2.1.5.2 says that codecvt<>::do_in and do_out should return the value noconv if "no conversion was needed". However, I don't see anything anywhere that defines what it means for a conversion to be needed or not needed. I can think of several circumstances where one might plausibly think that a conversion is not "needed", but I don't know which one is intended here.
Rationale:
Section: 20.2.2 [allocator.requirements] Status: NAD Submitter: Angelika Langer Opened: 1998-02-23 Last modified: 2006-12-30
View other active issues in [allocator.requirements].
View all other issues in [allocator.requirements].
View all issues with NAD status.
Discussion:
I couldn't find a statement in the standard saying whether the allocator object held by a container is held as a copy of the constructor argument or whether a pointer of reference is maintained internal. There is an according statement for compare objects and how they are maintained by the associative containers, but I couldn't find anything regarding allocators.
Did I overlook it? Is it an open issue or known defect? Or is it deliberately left unspecified?
Rationale:
Not a defect. The LWG believes that the Standard is already clear. See 23.2 [container.requirements], paragraph 8.
Section: 22.4.1.5 [locale.codecvt.byname] Status: Dup Submitter: Brendan Kehoe Opened: 1998-06-01 Last modified: 2006-12-30
View all other issues in [locale.codecvt.byname].
View all issues with Dup status.
Duplicate of: 33
Discussion:
Rationale:
Section: 27.8.3 [ostringstream] Status: NAD Submitter: Matthias Mueller Opened: 1998-05-27 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
In a comp.lang.c++.moderated Matthias Mueller wrote:
"We are not sure how to interpret the CD2 (see 27.3 [iostream.forward], 27.8.3.1 [ostringstream.cons], 27.8.1.1 [stringbuf.cons]) with respect to the question as to what the correct initial positions of the write and read pointers of a stringstream should be."
"Is it the same to output two strings or to initialize the stringstream with the first and to output the second?"
[PJ Plauger, Bjarne Stroustrup, Randy Smithey, Sean Corfield, and Jerry Schwarz have all offered opinions; see reflector messages lib-6518, 6519, 6520, 6521, 6523, 6524.]
Rationale:
The LWG believes the Standard is correct as written. The behavior of stringstreams is consistent with fstreams, and there is a constructor which can be used to obtain the desired effect. This behavior is known to be different from strstreams.
Section: 27.7.1.2.3 [istream::extractors] Status: NAD Submitter: Matt Austern Opened: 1998-07-01 Last modified: 2006-12-27
View all other issues in [istream::extractors].
View all issues with NAD status.
Discussion:
27.6.1.2.3 has member functions for extraction of signed char and unsigned char, both singly and as strings. However, it doesn't say what it means to extract a char from a basic_streambuf<charT, Traits>.
basic_streambuf, after all, has no members to extract a char, so basic_istream must somehow convert from charT to signed char or unsigned char. The standard doesn't say how it is to perform that conversion.
Rationale:
The Standard is correct as written. There is no such extractor and this is the intent of the LWG.
Section: D.7.1.3 [depr.strstreambuf.virtuals] Status: NAD Submitter: Matt Austern Opened: 1998-08-18 Last modified: 2006-12-27
View all other issues in [depr.strstreambuf.virtuals].
View all issues with NAD status.
Discussion:
The standard says how this member function affects the current stream position. (gptr or pptr) However, it does not say how this member function affects the beginning and end of the get/put area.
This is an issue when seekoff is used to position the get pointer beyond the end of the current read area. (Which is legal. This is implicit in the definition of seekhigh in D.7.1, paragraph 4.)
Rationale:
The LWG agrees that seekoff() is underspecified, but does not wish to invest effort in this deprecated feature.
Section: 21.4.8.9 [string.io] Status: Dup Submitter: Steve Clamage Opened: 1998-07-09 Last modified: 2006-12-30
View all other issues in [string.io].
View all issues with Dup status.
Duplicate of: 25
Discussion:
In a comp.std.c++ posting Michel Michaud wrote: What should be output by:
string text("Hello");
cout << '[' << setw(10) << right << text << ']';
Shouldn't it be:
[ Hello]
Another person replied: Actually, according to the FDIS, the width of the field should be the minimum of width and the length of the string, so the output shouldn't have any padding. I think that this is a typo, however, and that what is wanted is the maximum of the two. (As written, setw is useless for strings. If that had been the intent, one wouldn't expect them to have mentioned using its value.)
It's worth pointing out that this is a recent correction anyway; IIRC, earlier versions of the draft forgot to mention formatting parameters whatsoever.
Rationale:
Section: 22.4.1.4 [locale.codecvt] Status: Dup Submitter: Nathan Myers Opened: 1998-08-24 Last modified: 2006-12-30
View all other issues in [locale.codecvt].
View all issues with Dup status.
Duplicate of: 24
Discussion:
In 22.4.1.4 [locale.codecvt] par 3, and in 22.4.1.4.2 [locale.codecvt.virtuals] par 8, a nonexistent member function "do_convert" is mentioned. This member was replaced with "do_in" and "do_out", the proper referents in the contexts above.
Rationale:
Section: 27.9.1 [fstreams] Status: NAD Submitter: Matt Austern Opened: 1998-08-27 Last modified: 2006-12-27
View all other issues in [fstreams].
View all issues with NAD status.
Discussion:
Classes basic_ifstream, basic_ofstream, and basic_fstream all have a member function is_open. It should be a const member function, since it does nothing but call one of basic_filebuf's const member functions.
Rationale:
Not a defect. This is a deliberate feature; const streams would be meaningless.
Section: 26.6.2.3 [valarray.access] Status: Dup Submitter: Levente Farkas Opened: 1998-09-09 Last modified: 2007-10-11
View all other issues in [valarray.access].
View all issues with Dup status.
Duplicate of: 389
Discussion:
valarray:
T operator[] (size_t) const;
why not
const T& operator[] (size_t) const;
as in vector ???
One can't copy even from a const valarray eg:
memcpy(ptr, &v[0], v.size() * sizeof(double));
[I] find this bug in valarray is very difficult.
Rationale:
The LWG believes that the interface was deliberately designed that way. That is what valarray was designed to do; that's where the "value array" name comes from. LWG members further comment that "we don't want valarray to be a full STL container." 26.6.2.3 [valarray.access] specifies properties that indicate "an absence of aliasing" for non-constant arrays; this allows optimizations, including special hardware optimizations, that are not otherwise possible.
Section: 26.6.5 [template.slice.array], 26.6.7 [template.gslice.array], 26.6.8 [template.mask.array], 26.6.9 [template.indirect.array] Status: NAD Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2006-12-29
View all other issues in [template.slice.array].
View all issues with NAD status.
Discussion:
Isn't the definition of copy constructor and assignment operators wrong? Instead of
slice_array(const slice_array&); slice_array& operator=(const slice_array&);
IMHO they have to be
slice_array(const slice_array<T>&); slice_array& operator=(const slice_array<T>&);
Same for gslice_array.
Rationale:
Not a defect. The Standard is correct as written.
Section: 23.2.4 [associative.reqmts] Status: NAD Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2007-01-15
View other active issues in [associative.reqmts].
View all other issues in [associative.reqmts].
View all issues with NAD status.
Discussion:
Paragraph 5 specifies:
For set and multiset the value type is the same as the key type. For map and multimap it is equal to pair<const Key, T>.
Strictly speaking, this is not correct because for set and multiset the value type is the same as the constant key type.
Rationale:
Not a defect. The Standard is correct as written; it uses a different mechanism (const &) for set and multiset. See issue 103 for a related issue.
Section: 21.4.5 [string.access] Status: NAD Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
If I try
s.insert(0,1,' ');
I get an nasty ambiguity. It might be
s.insert((size_type)0,(size_type)1,(charT)' ');
which inserts 1 space character at position 0, or
s.insert((char*)0,(size_type)1,(charT)' ')
which inserts 1 space character at iterator/address 0 (bingo!), or
s.insert((char*)0, (InputIterator)1, (InputIterator)' ')
which normally inserts characters from iterator 1 to iterator ' '. But according to 23.1.1.9 (the "do the right thing" fix) it is equivalent to the second. However, it is still ambiguous, because of course I mean the first!
Rationale:
Not a defect. The LWG believes this is a "genetic misfortune" inherent in the design of string and thus not a defect in the Standard as such .
Section: 21 [strings] Status: NAD Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2006-12-27
View all other issues in [strings].
View all issues with NAD status.
Discussion:
The standard seems not to require that charT is equivalent to traits::char_type. So, what happens if charT is not equivalent to traits::char_type?
Rationale:
There is already wording in 21.2 [char.traits] paragraph 3 that requires them to be the same.
Section: 21.4.6.8 [string::swap] Status: Dup Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2006-12-30
View all other issues in [string::swap].
View all issues with Dup status.
Duplicate of: 5
Discussion:
The following compare() description is obviously a bug:
int compare(size_type pos, size_type n1,
charT *s, size_type n2 = npos) const;
because without passing n2 it should compare up to the end of the string instead of comparing npos characters (which throws an exception)
Rationale:
Section: 21.4.6.4 [string::insert], 21.4.6.2 [string::append] Status: NAD Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2006-12-27
View all other issues in [string::insert].
View all issues with NAD status.
Discussion:
Why does
template<class InputIterator>
basic_string& append(InputIterator first, InputIterator last);
return a string, while
template<class InputIterator>
void insert(iterator p, InputIterator first, InputIterator last);
returns nothing ?
Rationale:
The LWG believes this stylistic inconsistency is not sufficiently serious to constitute a defect.
Section: 21.4.6.4 [string::insert], 21.4.6.6 [string::replace] Status: Dup Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2006-12-30
View all other issues in [string::insert].
View all issues with Dup status.
Duplicate of: 83
Discussion:
All insert() and replace() members for strings with an iterator as first argument lack a throw specification. The throw specification should probably be: length_error if size exceeds maximum.
Rationale:
Considered a duplicate because it will be solved by the resolution of issue 83.
Section: 26.6 [numarray] Status: NAD Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2006-12-29
View all other issues in [numarray].
View all issues with NAD status.
Discussion:
You can easily create subsets, but you can't easily combine them with other subsets. Unfortunately, you almost always needs an explicit type conversion to valarray. This is because the standard does not specify that valarray subsets provide the same operations as valarrays.
For example, to multiply two subsets and assign the result to a third subset, you can't write the following:
va[slice(0,4,3)] = va[slice(1,4,3)] * va[slice(2,4,3)];
Instead, you have to code as follows:
va[slice(0,4,3)] = static_cast<valarray<double> >(va[slice(1,4,3)]) *
static_cast<valarray<double> >(va[slice(2,4,3)]);
This is tedious and error-prone. Even worse, it costs performance because each cast creates a temporary objects, which could be avoided without the cast.
Proposed resolution:
Extend all valarray subset types so that they offer all valarray operations.
Rationale:
This is not a defect in the Standard; it is a request for an extension.
Section: 17.6.4 [conforming] Status: NAD Submitter: Matt Austern Opened: 1998-01-22 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
Is it a permitted extension for library implementors to add template parameters to standard library classes, provided that those extra parameters have defaults? For example, instead of defining template <class T, class Alloc = allocator<T> > class vector; defining it as template <class T, class Alloc = allocator<T>, int N = 1> class vector;
The standard may well already allow this (I can't think of any way that this extension could break a conforming program, considering that users are not permitted to forward-declare standard library components), but it ought to be explicitly permitted or forbidden.
comment from Steve Cleary via comp.std.c++:
I disagree [with the proposed resolution] for the following reason: consider user library code with template template parameters. For example, a user library object may be templated on the type of underlying sequence storage to use (deque/list/vector), since these classes all take the same number and type of template parameters; this would allow the user to determine the performance tradeoffs of the user library object. A similar example is a user library object templated on the type of underlying set storage (set/multiset) or map storage (map/multimap), which would allow users to change (within reason) the semantic meanings of operations on that object.
I think that additional template parameters should be forbidden in the Standard classes. Library writers don't lose any expressive power, and can still offer extensions because additional template parameters may be provided by a non-Standard implementation class:
template <class T, class Allocator = allocator<T>, int N = 1> class __vector { ... }; template <class T, class Allocator = allocator<T> > class vector: public __vector<T, Allocator> { ... };
Proposed resolution:
Add a new subclause [presumably 17.4.4.9] following 17.6.4.10 [res.on.exception.handling]:
17.4.4.9 Template Parameters
A specialization of a template class described in the C++ Standard Library behaves the same as if the implementation declares no additional template parameters.
Footnote: Additional template parameters with default values are thus permitted.
Add "template parameters" to the list of subclauses at the end of 17.6.4 [conforming] paragraph 1.
[Kona: The LWG agreed the standard needs clarification. After discussion with John Spicer, it seems added template parameters can be detected by a program using template-template parameters. A straw vote - "should implementors be allowed to add template parameters?" found no consensus ; 5 - yes, 7 - no.]
Rationale:
There is no ambiguity; the standard is clear as written. Library implementors are not permitted to add template parameters to standard library classes. This does not fall under the "as if" rule, so it would be permitted only if the standard gave explicit license for implementors to do this. This would require a change in the standard.
The LWG decided against making this change, because it would break user code involving template template parameters or specializations of standard library class templates.
Section: 17.6.4.5 [member.functions] Status: NAD Submitter: AFNOR Opened: 1998-10-07 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
In 17.3.4.4/2 vs 17.3.4.7/0 there is a hole; an implementation could add virtual members a base class and break user derived classes.
Example:
// implementation code:
struct _Base { // _Base is in the implementer namespace
virtual void foo ();
};
class vector : _Base // deriving from a class is allowed
{ ... };
// user code:
class vector_checking : public vector
{
void foo (); // don't want to override _Base::foo () as the
// user doesn't know about _Base::foo ()
};
Proposed resolution:
Clarify the wording to make the example illegal.
Rationale:
This is not a defect in the Standard. The example is already illegal. See 17.6.4.5 [member.functions] paragraph 2.
Section: 23 [containers] Status: NAD Submitter: AFNOR Opened: 1998-10-07 Last modified: 2006-12-27
View other active issues in [containers].
View all other issues in [containers].
View all issues with NAD status.
Discussion:
insert(iterator, const value_type&) is defined both on sequences and on set, with unrelated semantics: insert here (in sequences), and insert with hint (in associative containers). They should have different names (B.S. says: do not abuse overloading).
Rationale:
This is not a defect in the Standard. It is a genetic misfortune of the design, for better or for worse.
Section: 24.5.1.3.13 [reverse.iter.op==] Status: NAD Submitter: AFNOR Opened: 1998-10-07 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
The <, >, <=, >= comparison operator are wrong: they return the opposite of what they should.
Note: same problem in CD2, these were not even defined in CD1. SGI STL code is correct; this problem is known since the Morristown meeting but there it was too late
Rationale:
This is not a defect in the Standard. A careful reading shows the Standard is correct as written. A review of several implementations show that they implement exactly what the Standard says.
Section: 24.5.2 [insert.iterators], 24.6.4 [ostreambuf.iterator] Status: NAD Submitter: AFNOR Opened: 1998-10-07 Last modified: 2006-12-27
View other active issues in [insert.iterators].
View all other issues in [insert.iterators].
View all issues with NAD status.
Discussion:
Overspecified For an insert iterator it, the expression *it is required to return a reference to it. This is a simple possible implementation, but as the SGI STL documentation says, not the only one, and the user should not assume that this is the case.
Rationale:
The LWG believes this causes no harm and is not a defect in the standard. The only example anyone could come up with caused some incorrect code to work, rather than the other way around.
Section: 23.3.6 [vector], 23.3.1 [array] Status: NAD Submitter: AFNOR Opened: 1998-10-07 Last modified: 2007-02-19
View other active issues in [vector].
View all other issues in [vector].
View all issues with NAD status.
Discussion:
Reserve can not free storage, unlike string::reserve
Rationale:
This is not a defect in the Standard. The LWG has considered this issue in the past and sees no need to change the Standard. Deque has no reserve() member function. For vector, shrink-to-fit can be expressed in a single line of code (where v is vector<T>):
vector<T>(v).swap(v); // shrink-to-fit v
Section: 23.2.4 [associative.reqmts] Status: Dup Submitter: AFNOR Opened: 1998-10-07 Last modified: 2006-12-30
View other active issues in [associative.reqmts].
View all other issues in [associative.reqmts].
View all issues with Dup status.
Duplicate of: 264
Discussion:
Table 69 of Containers say that a.insert(i,j) is linear if [i, j) is ordered. It seems impossible to implement, as it means that if [i, j) = [x], insert in an associative container is O(1)!
Proposed resolution:
N+log (size()) if [i,j) is sorted according to value_comp()
Rationale:
Subsumed by issue 264.
Section: 21.4.4 [string.capacity] Status: NAD Submitter: AFNOR Opened: 1998-10-07 Last modified: 2006-12-27
View all other issues in [string.capacity].
View all issues with NAD status.
Discussion:
It is not clear that undefined behavior applies when pos == size () for the non const version.
Proposed resolution:
Rewrite as: Otherwise, if pos > size () or pos == size () and the non-const version is used, then the behavior is undefined.
Rationale:
The Standard is correct. The proposed resolution already appears in the Standard.
Section: 27.9 [file.streams] Status: Dup Submitter: AFNOR Opened: 1998-10-07 Last modified: 2008-01-05
View all issues with Dup status.
Duplicate of: 454
Discussion:
fstream ctors take a const char* instead of string.
fstream ctors can't take wchar_t
An extension to add a const wchar_t* to fstream would make the implementation non conforming.
Rationale:
This is not a defect in the Standard. It might be an interesting extension for the next Standard.
Section: 26.6.2 [template.valarray] Status: NAD Submitter: AFNOR Opened: 1998-10-07 Last modified: 2006-12-29
View all other issues in [template.valarray].
View all issues with NAD status.
Discussion:
The order of the arguments is (elem, size) instead of the normal (size, elem) in the rest of the library. Since elem often has an integral or floating point type, both types are convertible to each other and reversing them leads to a well formed program.
Proposed resolution:
Inverting the arguments could silently break programs. Introduce the two signatures (const T&, size_t) and (size_t, const T&), but make the one we do not want private so errors result in a diagnosed access violation. This technique can also be applied to STL containers.
Rationale:
The LWG believes that while the order of arguments is unfortunate, it does not constitute a defect in the standard. The LWG believes that the proposed solution will not work for valarray<size_t> and perhaps other cases.
Section: 24.6.3.5 [istreambuf.iterator::equal] Status: NAD Submitter: Nathan Myers Opened: 1998-10-15 Last modified: 2009-07-14
View all other issues in [istreambuf.iterator::equal].
View all issues with NAD status.
Discussion:
The member istreambuf_iterator<>::equal is specified to be unnecessarily inefficient. While this does not affect the efficiency of conforming implementations of iostreams, because they can "reach into" the iterators and bypass this function, it does affect users who use istreambuf_iterators.
The inefficiency results from a too-scrupulous definition, which requires a "true" result if neither iterator is at eof. In practice these iterators can only usefully be compared with the "eof" value, so the extra test implied provides no benefit, but slows down users' code.
The solution is to weaken the requirement on the function to return true only if both iterators are at eof.
[ Summit: ]
Reopened by Alisdair.
[ Post Summit Daniel adds: ]
Recommend NAD. The proposed wording would violate the axioms of concept requirement EqualityComparable axioms as part of concept InputIterator and more specifically it would violate the explicit wording of 24.2.1 [input.iterators]/7:
If two iterators a and b of the same type are equal, then either a and b are both dereferenceable or else neither is dereferenceable.[ 2009-07 Frankfurt ]
Agree NAD.
Proposed resolution:
Replace 24.6.3.5 [istreambuf.iterator::equal], paragraph 1,
-1- Returns: true if and only if both iterators are at end-of-stream, or neither is at end-of-stream, regardless of what streambuf object they use.
with
-1- Returns: true if and only if both iterators are at end-of-stream, regardless of what streambuf object they use.
Rationale:
It is not clear that this is a genuine defect. Additionally, the LWG was reluctant to make a change that would result in operator== not being a equivalence relation. One consequence of this change is that an algorithm that's passed the range [i, i) would no longer treat it as an empty range.
Section: 27.7.1.1 [istream], 27.7.1.3 [istream.unformatted] Status: NAD Submitter: Steve Clamage Opened: 1998-10-13 Last modified: 2006-12-27
View all other issues in [istream].
View all issues with NAD status.
Discussion:
In 27.6.1.1, class basic_istream has a member function sync, described in 27.6.1.3, paragraph 36.
Following the chain of definitions, I find that the various sync functions have defined semantics for output streams, but no semantics for input streams. On the other hand, basic_ostream has no sync function.
The sync function should at minimum be added to basic_ostream, for internal consistency.
A larger question is whether sync should have assigned semantics for input streams.
Classic iostreams said streambuf::sync flushes pending output and attempts to return unread input characters to the source. It is a protected member function. The filebuf version (which is public) has that behavior (it backs up the read pointer). Class strstreambuf does not override streambuf::sync, and so sync can't be called on a strstream.
If we can add corresponding semantics to the various sync functions, we should. If not, we should remove sync from basic_istream.
Rationale:
A sync function is not needed in basic_ostream because the flush function provides the desired functionality.
As for the other points, the LWG finds the standard correct as written.
Section: 20.3.7 [template.bitset] Status: Dup Submitter: Judy Ward Opened: 1998-11-06 Last modified: 2008-03-14
View other active issues in [template.bitset].
View all other issues in [template.bitset].
View all issues with Dup status.
Duplicate of: 778
Discussion:
The following code does not compile with the EDG compiler:
#include <bitset>
using namespace std;
bitset<32> b("111111111");
If you cast the ctor argument to a string, i.e.:
bitset<32> b(string("111111111"));
then it will compile. The reason is that bitset has the following templatized constructor:
template <class charT, class traits, class Allocator> explicit bitset (const basic_string<charT, traits, Allocator>& str, ...);
According to the compiler vendor, Steve Adamcyk at EDG, the user cannot pass this template constructor a const char* and expect a conversion to basic_string. The reason is "When you have a template constructor, it can get used in contexts where type deduction can be done. Type deduction basically comes up with exact matches, not ones involving conversions."
I don't think the intention when this constructor became templatized was for construction from a const char* to no longer work.
Proposed resolution:
Add to 20.3.7 [template.bitset] a bitset constructor declaration
explicit bitset(const char*);
and in Section 20.3.7.1 [bitset.cons] add:
explicit bitset(const char* str);Effects:
Calls bitset((string) str, 0, string::npos);
Rationale:
Although the problem is real, the standard is designed that way so it is not a defect. Education is the immediate workaround. A future standard may wish to consider the Proposed Resolution as an extension.
Section: 22.3.1.1.1 [locale.category] Status: NAD Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2006-12-27
View all other issues in [locale.category].
View all issues with NAD status.
Discussion:
Section 22.1.1.1.1 has the following listed in Table 51: ctype<char> , ctype<wchar_t>.
Also Section 22.4.1.1 [locale.ctype] says:
The instantiations required in Table 51 (22.1.1.1.1) namely ctype<char> and ctype<wchar_t> , implement character classing appropriate to the implementation's native character set.
However, Section 22.4.1.3 [facet.ctype.special] only has a detailed description of the ctype<char> specialization, not the ctype<wchar_t> specialization.
Proposed resolution:
Add the ctype<wchar_t> detailed class description to Section 22.4.1.3 [facet.ctype.special].
Rationale:
Specialization for wchar_t is not needed since the default is acceptable.
Section: 27.8 [string.streams], 27.9 [file.streams] Status: NAD Submitter: Angelika Langer Opened: 1999-02-22 Last modified: 2009-07-14
View all other issues in [string.streams].
View all issues with NAD status.
Discussion:
The following question came from Thorsten Herlemann:
You can set a mode when constructing or opening a file-stream or filebuf, e.g. ios::in, ios::out, ios::binary, ... But how can I get that mode later on, e.g. in my own operator << or operator >> or when I want to check whether a file-stream or file-buffer object passed as parameter is opened for input or output or binary? Is there no possibility? Is this a design-error in the standard C++ library?
It is indeed impossible to find out what a stream's or stream buffer's open mode is, and without that knowledge you don't know how certain operations behave. Just think of the append mode.
Both streams and stream buffers should have a mode() function that returns the current open mode setting.
[ post Bellevue: Alisdair requested to re-Open. ]
[ 2009-07 Frankfurt ]
Neither Howard nor Bill has received a customer request for this.
No consensus for change. The programmer can save this information to the side.
Moved to NAD.
Proposed resolution:
For stream buffers, add a function to the base class as a non-virtual function qualified as const to 27.6.2 [streambuf]:
openmode mode() const;
Returns the current open mode.
With streams, I'm not sure what to suggest. In principle, the mode could already be returned by ios_base, but the mode is only initialized for file and string stream objects, unless I'm overlooking anything. For this reason it should be added to the most derived stream classes. Alternatively, it could be added to basic_ios and would be default initialized in basic_ios<>::init().
Rationale:
This might be an interesting extension for some future, but it is not a defect in the current standard. The Proposed Resolution is retained for future reference.
Section: 23.3.4.4 [list.ops] Status: NAD Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2007-02-19
View other active issues in [list.ops].
View all other issues in [list.ops].
View all issues with NAD status.
Discussion:
What happens if a splice operation causes the size() of a list to grow beyond max_size()?
Rationale:
Size() cannot grow beyond max_size().
Section: 27.7.1.5.1 [iostream.cons] Status: NAD Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
-1- Effects Constructs an object of class basic_iostream, assigning initial values to the base classes by calling basic_istream<charT,traits>(sb) (lib.istream) and basic_ostream<charT,traits>(sb) (lib.ostream)
The called for basic_istream and basic_ostream constructors call init(sb). This means that the basic_iostream's virtual base class is initialized twice.
Proposed resolution:
Change 27.6.1.5.1, paragraph 1 to:
-1- Effects Constructs an object of class basic_iostream, assigning initial values to the base classes by calling basic_istream<charT,traits>(sb) (lib.istream).
Rationale:
The LWG agreed that the init() function is called twice, but said that this is harmless and so not a defect in the standard.
Section: 22.4.1.4 [locale.codecvt] Status: NAD Submitter: Angelika Langer Opened: 1999-03-18 Last modified: 2009-07-14
View all other issues in [locale.codecvt].
View all issues with NAD status.
Discussion:
Section 22.4.1.4 [locale.codecvt] specifies that ctype_byname<char> must be a specialization of the ctype_byname template.
It is common practice in the standard that specializations of class templates are only mentioned where the interface of the specialization deviates from the interface of the template that it is a specialization of. Otherwise, the fact whether or not a required instantiation is an actual instantiation or a specialization is left open as an implementation detail.
Clause 22.2.1.4 deviates from that practice and for that reason is misleading. The fact, that ctype_byname<char> is specified as a specialization suggests that there must be something "special" about it, but it has the exact same interface as the ctype_byname template. Clause 22.2.1.4 does not have any explanatory value, is at best redundant, at worst misleading - unless I am missing anything.
Naturally, an implementation will most likely implement ctype_byname<char> as a specialization, because the base class ctype<char> is a specialization with an interface different from the ctype template, but that's an implementation detail and need not be mentioned in the standard.
[ Summit: ]
Reopened by Alisdair.
[ 2009-07 Frankfurt ]
Moved to NAD.
Rationale:
The standard as written is mildly misleading, but the correct fix is to deal with the underlying problem in the ctype_byname base class, not in the specialization. See issue 228.
Section: 23.4.1 [map] Status: NAD Editorial Submitter: Mark Mitchell Opened: 1999-04-14 Last modified: 2008-03-14
View all other issues in [map].
View all issues with NAD Editorial status.
Discussion:
23.2 [container.requirements]
expression return type pre/post-condition
------------- ----------- -------------------
X::value_type T T is assignable
23.4.1 [map]
A map satisfies all the requirements of a container.
For a map<Key, T> ... the value_type is pair<const Key, T>.
There's a contradiction here. In particular, `pair<const Key, T>' is not assignable; the `const Key' cannot be assigned to. So, map<Key, T>::value_type does not satisfy the assignable requirement imposed by a container.
[See issue 103 for the slightly related issue of modification of set keys.]
Rationale:
The LWG believes that the standard is inconsistent, but that this is a design problem rather than a strict defect. May wish to reconsider for the next standard.
Section: D.5 [depr.c.headers] Status: NAD Submitter: Christophe de Dinechin Opened: 1999-05-04 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
[depr.c.headers] paragraph 2 reads:
Each C header, whose name has the form name.h, behaves as if each name placed in the Standard library namespace by the corresponding cname header is also placed within the namespace scope of the namespace std and is followed by an explicit using-declaration (_namespace.udecl_)
I think it should mention the global name space somewhere... Currently, it indicates that name placed in std is also placed in std...
I don't know what is the correct wording. For instance, if struct tm is defined in time.h, ctime declares std::tm. However, the current wording seems ambiguous regarding which of the following would occur for use of both ctime and time.h:
// version 1:
namespace std {
struct tm { ... };
}
using std::tm;
// version 2:
struct tm { ... };
namespace std {
using ::tm;
}
// version 3:
struct tm { ... };
namespace std {
struct tm { ... };
}
I think version 1 is intended.
[Kona: The LWG agreed that the wording is not clear. It also agreed that version 1 is intended, version 2 is not equivalent to version 1, and version 3 is clearly not intended. The example below was constructed by Nathan Myers to illustrate why version 2 is not equivalent to version 1.
Although not equivalent, the LWG is unsure if (2) is enough of a problem to be prohibited. Points discussed in favor of allowing (2):
- It may be a convenience to implementors.
- The only cases that fail are structs, of which the C library contains only a few.
]
Example:
#include <time.h>
#include <utility>
int main() {
std::tm * t;
make_pair( t, t ); // okay with version 1 due to Koenig lookup
// fails with version 2; make_pair not found
return 0;
}
Proposed resolution:
Replace D.5 [depr.c.headers] paragraph 2 with:
Each C header, whose name has the form name.h, behaves as if each name placed in the Standard library namespace by the corresponding cname header is also placed within the namespace scope of the namespace std by name.h and is followed by an explicit using-declaration (_namespace.udecl_) in global scope.
Rationale:
The current wording in the standard is the result of a difficult compromise that averted delay of the standard. Based on discussions in Tokyo it is clear that there is no still no consensus on stricter wording, so the issue has been closed. It is suggested that users not write code that depends on Koenig lookup of C library functions.
Section: 27.5.4.1 [basic.ios.cons] Status: NAD Submitter: Angelika Langer Opened: 1999-05-12 Last modified: 2006-12-27
View all other issues in [basic.ios.cons].
View all issues with NAD status.
Discussion:
There is no initial value for the adjustfield defined, although many people believe that the default adjustment were right. This is a common misunderstanding. The standard only defines that, if no adjustment is specified, all the predefined inserters must add fill characters before the actual value, which is "as if" the right flag were set. The flag itself need not be set.
When you implement a user-defined inserter you cannot rely on right being the default setting for the adjustfield. Instead, you must be prepared to find none of the flags set and must keep in mind that in this case you should make your inserter behave "as if" the right flag were set. This is surprising to many people and complicates matters more than necessary.
Unless there is a good reason why the adjustfield should not be initialized I would suggest to give it the default value that everybody expects anyway.
Rationale:
This is not a defect. It is deliberate that the default is no bits set. Consider Arabic or Hebrew, for example. See 22.4.2.2.2 [facet.num.put.virtuals] paragraph 19, Table 61 - Fill padding.
Section: 27.5.2.5 [ios.base.storage] Status: Dup Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2007-01-15
View all other issues in [ios.base.storage].
View all issues with Dup status.
Duplicate of: 41
Discussion:
According to paragraphs 2 and 4 of 27.5.2.5 [ios.base.storage], the functions iword() and pword() "set the badbit (which might throw an exception)" on failure. ... but what does it mean for ios_base to set the badbit? The state facilities of the IOStream library are defined in basic_ios, a derived class! It would be possible to attempt a down cast but then it would be necessary to know the character type used...
Rationale:
Section: 27.7.1.2.3 [istream::extractors] Status: Dup Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2007-01-15
View all other issues in [istream::extractors].
View all issues with Dup status.
Duplicate of: 60
Discussion:
It appears to be somewhat nonsensical to consider the functions defined in the paragraphs 1 to 5 to be "Formatted input function" but since these functions are defined in a section labeled "Formatted input functions" it is unclear to me whether these operators are considered formatted input functions which have to conform to the "common requirements" from 27.7.1.2.1 [istream.formatted.reqmts]: If this is the case, all manipulators, not just ws, would skip whitespace unless noskipws is set (... but setting noskipws using the manipulator syntax would also skip whitespace :-)
See also issue 166 for the same problem in formatted output
Rationale:
Section: 27.7.1.3 [istream.unformatted] Status: Dup Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2007-01-15
View all other issues in [istream.unformatted].
View all issues with Dup status.
Duplicate of: 60
Discussion:
It is not clear which functions are to be considered unformatted input functions. As written, it seems that all functions in 27.7.1.3 [istream.unformatted] are unformatted input functions. However, it does not really make much sense to construct a sentry object for gcount(), sync(), ... Also it is unclear what happens to the gcount() if eg. gcount(), putback(), unget(), or sync() is called: These functions don't extract characters, some of them even "unextract" a character. Should this still be reflected in gcount()? Of course, it could be read as if after a call to gcount() gcount() return 0 (the last unformatted input function, gcount(), didn't extract any character) and after a call to putback() gcount() returns -1 (the last unformatted input function putback() did "extract" back into the stream). Correspondingly for unget(). Is this what is intended? If so, this should be clarified. Otherwise, a corresponding clarification should be used.
Rationale:
Section: 27.7.2.6.3 [ostream.inserters] Status: Dup Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2007-01-15
View all issues with Dup status.
Duplicate of: 60
Discussion:
From 27.7.2.6.1 [ostream.formatted.reqmts] it appears that all the functions defined in 27.7.2.6.3 [ostream.inserters] have to construct a sentry object. Is this really intended?
This is basically the same problem as issue 162 but for output instead of input.
Rationale:
Section: 26.4.6 [complex.ops] Status: NAD Submitter: Judy Ward Opened: 1999-07-02 Last modified: 2006-12-27
View all other issues in [complex.ops].
View all issues with NAD status.
Discussion:
A user who tries to explicitly instantiate a complex non-member operator will get compilation errors. Below is a simplified example of the reason why. The problem is that iterator_traits cannot be instantiated on a non-pointer type like float, yet when the compiler is trying to decide which operator+ needs to be instantiated it must instantiate the declaration to figure out the first argument type of a reverse_iterator operator.
namespace std {
template <class Iterator>
struct iterator_traits
{
typedef typename Iterator::value_type value_type;
};
template <class T> class reverse_iterator;
// reverse_iterator operator+
template <class T>
reverse_iterator<T> operator+
(typename iterator_traits<T>::difference_type, const reverse_iterator<T>&);
template <class T> struct complex {};
// complex operator +
template <class T>
complex<T> operator+ (const T& lhs, const complex<T>& rhs)
{ return complex<T>();}
}
// request for explicit instantiation
template std::complex<float> std::operator+<float>(const float&,
const std::complex<float>&);
See also c++-stdlib reflector messages: lib-6814, 6815, 6816.
Rationale:
Implementors can make minor changes and the example will work. Users are not affected in any case.
According to John Spicer, It is possible to explicitly instantiate these operators using different syntax: change "std::operator+<float>" to "std::operator+".
The proposed resolution of issue 120 is that users will not be able to explicitly instantiate standard library templates. If that resolution is accepted then library implementors will be the only ones that will be affected by this problem, and they must use the indicated syntax.
Section: 27.4.1 [narrow.stream.objects] Status: NAD Submitter: Judy Ward Opened: 1999-07-02 Last modified: 2006-12-27
View all other issues in [narrow.stream.objects].
View all issues with NAD status.
Discussion:
Section 27.3.1 says "After the object cerr is initialized, cerr.flags() & unitbuf is nonzero. Its state is otherwise the same as required for ios_base::init (lib.basic.ios.cons). It doesn't say anything about the the state of clog. So this means that calling cerr.tie() and clog.tie() should return 0 (see Table 89 for ios_base::init effects).
Neither of the popular standard library implementations that I tried does this, they both tie cerr and clog to &cout. I would think that would be what users expect.
Rationale:
The standard is clear as written.
27.3.1/5 says that "After the object cerr is initialized, cerr.flags() & unitbuf is nonzero. Its state is otherwise the same as required for ios_base::init (27.4.4.1)." Table 89 in 27.4.4.1, which gives the postconditions of basic_ios::init(), says that tie() is 0. (Other issues correct ios_base::init to basic_ios::init().)
Section: 26.6.2.6 [valarray.cassign] Status: NAD Submitter: Gabriel Dos Reis Opened: 1999-08-15 Last modified: 2008-03-11
View all issues with NAD status.
Discussion:
26.5.2.6 defines augmented assignment operators valarray<T>::op=(const T&), but fails to provide corresponding versions for the helper classes. Thus making the following illegal:
#include <valarray>
int main()
{
std::valarray<double> v(3.14, 1999);
v[99] *= 2.0; // Ok
std::slice s(0, 50, 2);
v[s] *= 2.0; // ERROR
}
I can't understand the intent of that omission. It makes the valarray library less intuitive and less useful.
Rationale:
Although perhaps an unfortunate design decision, the omission is not a defect in the current standard. A future standard may wish to add the missing operators.
Section: 25.4.7 [alg.min.max] Status: NAD Submitter: Mark Rintoul Opened: 1999-08-26 Last modified: 2009-07-14
View all other issues in [alg.min.max].
View all issues with NAD status.
Discussion:
Both std::min and std::max are defined as template functions. This
is very different than the definition of std::plus (and similar
structs) which are defined as function objects which inherit
std::binary_function.
This lack of inheritance leaves std::min and std::max somewhat useless in standard library algorithms which require
a function object that inherits std::binary_function.
[ post Bellevue: Alisdair requested to re-Open. ]
[ 2009-07 Frankfurt ]
C++0x has lambdas to address this problem now.
Moved to NAD.
Rationale:
Although perhaps an unfortunate design decision, the omission is not a defect in the current standard. A future standard may wish to consider additional function objects.
Section: 25.4.3 [alg.binary.search] Status: NAD Submitter: Nico Josuttis Opened: 1999-10-10 Last modified: 2006-12-27
View all other issues in [alg.binary.search].
View all issues with NAD status.
Discussion:
The complexity of binary_search() is stated as "At most
log(last-first) + 2 comparisons", which seems to say that the
algorithm has logarithmic complexity. However, this algorithms is
defined for forward iterators. And for forward iterators, the need to
step element-by-element results into linear complexity. But such a
statement is missing in the standard. The same applies to
lower_bound(), upper_bound(), and equal_range().
However, strictly speaking the standard contains no bug here. So this
might considered to be a clarification or improvement.
Rationale:
The complexity is expressed in terms of comparisons, and that complexity can be met even if the number of iterators accessed is linear. Paragraph 1 already says exactly what happens to iterators.
Section: 23.2.4 [associative.reqmts] Status: NAD Submitter: Ed Brey Opened: 1999-06-06 Last modified: 2006-12-30
View other active issues in [associative.reqmts].
View all other issues in [associative.reqmts].
View all issues with NAD status.
Duplicate of: 233
Discussion:
As defined in 23.1.2, paragraph 7 (table 69), a.insert(p,t) suffers from several problems:
| expression | return type | pre/post-condition | complexity |
| a.insert(p,t) | iterator | inserts t if and only if there is no element with key equivalent to the key of t in containers with unique keys; always inserts t in containers with equivalent keys. always returns the iterator pointing to the element with key equivalent to the key of t . iterator p is a hint pointing to where the insert should start to search. | logarithmic in general, but amortized constant if t is inserted right after p . |
1. For a container with unique keys, only logarithmic complexity is guaranteed if no element is inserted, even though constant complexity is always possible if p points to an element equivalent to t.
2. For a container with equivalent keys, the amortized constant complexity guarantee is only useful if no key equivalent to t exists in the container. Otherwise, the insertion could occur in one of multiple locations, at least one of which would not be right after p.
3. By guaranteeing amortized constant complexity only when t is inserted after p, it is impossible to guarantee constant complexity if t is inserted at the beginning of the container. Such a problem would not exist if amortized constant complexity was guaranteed if t is inserted before p, since there is always some p immediately before which an insert can take place.
4. For a container with equivalent keys, p does not allow specification of where to insert the element, but rather only acts as a hint for improving performance. This negates the added functionality that p would provide if it specified where within a sequence of equivalent keys the insertion should occur. Specifying the insert location provides more control to the user, while providing no disadvantage to the container implementation.
Proposed resolution:
In 23.2.4 [associative.reqmts] paragraph 7, replace the row in table 69 for a.insert(p,t) with the following two rows:
| expression | return type | pre/post-condition | complexity |
| a_uniq.insert(p,t) | iterator | inserts t if and only if there is no element with key equivalent to the key of t. returns the iterator pointing to the element with key equivalent to the key of t. | logarithmic in general, but amortized constant if t is inserted right before p or p points to an element with key equivalent to t. |
| a_eq.insert(p,t) | iterator | inserts t and returns the iterator pointing to the newly inserted element. t is inserted right before p if doing so preserves the container ordering. | logarithmic in general, but amortized constant if t is inserted right before p. |
Rationale:
Too big a change. Furthermore, implementors report checking both before p and after p, and don't want to change this behavior.
Section: 27.5.4 [ios] Status: NAD Submitter: Steve Clamage Opened: 1999-09-07 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
In classic iostreams, base class ios had an rdbuf function that returned a pointer to the associated streambuf. Each derived class had its own rdbuf function that returned a pointer of a type reflecting the actual type derived from streambuf. Because in ARM C++, virtual function overrides had to have the same return type, rdbuf could not be virtual.
In standard iostreams, we retain the non-virtual rdbuf function design, and in addition have an overloaded rdbuf function that sets the buffer pointer. There is no need for the second function to be virtual nor to be implemented in derived classes.
Minor question: Was there a specific reason not to make the original rdbuf function virtual?
Major problem: Friendly compilers warn about functions in derived classes that hide base-class overloads. Any standard implementation of iostreams will result in such a warning on each of the iostream classes, because of the ill-considered decision to overload rdbuf only in a base class.
In addition, users of the second rdbuf function must use explicit qualification or a cast to call it from derived classes. An explicit qualification or cast to basic_ios would prevent access to any later overriding version if there was one.
What I'd like to do in an implementation is add a using- declaration for the second rdbuf function in each derived class. It would eliminate warnings about hiding functions, and would enable access without using explicit qualification. Such a change I don't think would change the behavior of any valid program, but would allow invalid programs to compile:
filebuf mybuf; fstream f; f.rdbuf(mybuf); // should be an error, no visible rdbuf
I'd like to suggest this problem as a defect, with the proposed resolution to require the equivalent of a using-declaration for the rdbuf function that is not replaced in a later derived class. We could discuss whether replacing the function should be allowed.
Rationale:
For historical reasons, the standard is correct as written. There is a subtle difference between the base class rdbuf() and derived class rdbuf(). The derived class rdbuf() always returns the original streambuf, whereas the base class rdbuf() will return the "current streambuf" if that has been changed by the variant you mention.
Permission is not required to add such an extension. See 17.6.4.5 [member.functions].
Section: 18.6.1.3 [new.delete.placement] Status: Dup Submitter: Herb Sutter Opened: 1998-12-15 Last modified: 2006-12-30
View all other issues in [new.delete.placement].
View all issues with Dup status.
Duplicate of: 114
Discussion:
The example in 18.6.1.3 [new.delete.placement] paragraph 4 reads:
[Example: This can be useful for constructing an object at a known address:
char place[sizeof(Something)];
Something* p = new (place) Something();
end example]
This example has potential alignment problems.
Rationale:
Section: 20.2.2 [allocator.requirements], 23.2 [container.requirements] Status: NAD Submitter: Andy Sawyer Opened: 1999-10-21 Last modified: 2006-12-30
View other active issues in [allocator.requirements].
View all other issues in [allocator.requirements].
View all issues with NAD status.
Discussion:
Must the value returned by max_size() be unchanged from call to call?
Must the value returned from max_size() be meaningful?
Possible meanings identified in lib-6827:
1) The largest container the implementation can support given "best
case" conditions - i.e. assume the run-time platform is "configured to
the max", and no overhead from the program itself. This may possibly
be determined at the point the library is written, but certainly no
later than compile time.
2) The largest container the program could create, given "best case"
conditions - i.e. same platform assumptions as (1), but take into
account any overhead for executing the program itself. (or, roughly
"storage=storage-sizeof(program)"). This does NOT include any resource
allocated by the program. This may (or may not) be determinable at
compile time.
3) The largest container the current execution of the program could
create, given knowledge of the actual run-time platform, but again,
not taking into account any currently allocated resource. This is
probably best determined at program start-up.
4) The largest container the current execution program could create at
the point max_size() is called (or more correctly at the point
max_size() returns :-), given it's current environment (i.e. taking
into account the actual currently available resources). This,
obviously, has to be determined dynamically each time max_size() is
called.
Proposed resolution:
Rationale:
max_size() isn't useful for very many things, and the existing wording is sufficiently clear for the few cases that max_size() can be used for. None of the attempts to change the existing wording were an improvement.
It is clear to the LWG that the value returned by max_size() can't change from call to call.
Section: 27.7.1.1.3 [istream::sentry] Status: NAD Submitter: Matt McClure and Dietmar Kühl Opened: 2000-01-01 Last modified: 2007-01-15
View all other issues in [istream::sentry].
View all issues with NAD status.
Discussion:
27.6.1.1.2 Paragraph 4 states:
To decide if the character c is a whitespace character, the constructor performs ''as if'' it executes the following code fragment:
const ctype<charT>& ctype = use_facet<ctype<charT> >(is.getloc()); if (ctype.is(ctype.space,c)!=0) // c is a whitespace character.
But Table 51 in 22.1.1.1.1 only requires an implementation to provide specializations for ctype<char> and ctype<wchar_t>. If sentry's constructor is implemented using ctype, it will be uninstantiable for a user-defined character type charT, unless the implementation has provided non-working (since it would be impossible to define a correct ctype<charT> specialization for an arbitrary charT) definitions of ctype's virtual member functions.
It seems the intent the standard is that sentry should behave, in every respect, not just during execution, as if it were implemented using ctype, with the burden of providing a ctype specialization falling on the user. But as it is written, nothing requires the translation of sentry's constructor to behave as if it used the above code, and it would seem therefore, that sentry's constructor should be instantiable for all character types.
Note: If I have misinterpreted the intent of the standard with respect to sentry's constructor's instantiability, then a note should be added to the following effect:
An implementation is forbidden from using the above code if it renders the constructor uninstantiable for an otherwise valid character type.
In any event, some clarification is needed.
Rationale:
It is possible but not easy to instantiate on types other than char or wchar_t; many things have to be done first. That is by intention and is not a defect.
Section: 24.4.4 [iterator.operations] Status: NAD Submitter: Rintala Matti Opened: 2000-01-28 Last modified: 2008-09-30
View other active issues in [iterator.operations].
View all other issues in [iterator.operations].
View all issues with NAD status.
Discussion:
Section 24.3.4 describes the function distance(first, last) (where first and last are iterators) which calculates "the number of increments or decrements needed to get from 'first' to 'last'".
The function should work for forward, bidirectional and random access iterators, and there is a requirement 24.3.4.5 which states that "'last' must be reachable from 'first'".
With random access iterators the function is easy to implement as "last - first".
With forward iterators it's clear that 'first' must point to a place before 'last', because otherwise 'last' would not be reachable from 'first'.
But what about bidirectional iterators? There 'last' is reachable from 'first' with the -- operator even if 'last' points to an earlier position than 'first'. However, I cannot see how the distance() function could be implemented if the implementation does not know which of the iterators points to an earlier position (you cannot use ++ or -- on either iterator if you don't know which direction is the "safe way to travel").
The paragraph 24.3.4.1 states that "for ... bidirectional iterators they use ++ to provide linear time implementations". However, the ++ operator is not mentioned in the reachability requirement. Furthermore 24.3.4.4 explicitly mentions that distance() returns the number of increments _or decrements_, suggesting that it could return a negative number also for bidirectional iterators when 'last' points to a position before 'first'.
Is a further requirement is needed to state that for forward and bidirectional iterators "'last' must be reachable from 'first' using the ++ operator". Maybe this requirement might also apply to random access iterators so that distance() would work the same way for every iterator category?
Rationale:
"Reachable" is defined in the standard in X [iterator.concepts] paragraph 6. The definition is only in terms of operator++(). The LWG sees no defect in the standard.
Section: 18.3.1.2 [numeric.limits.members] Status: NAD Submitter: Steve Cleary Opened: 2000-01-28 Last modified: 2006-12-27
View all other issues in [numeric.limits.members].
View all issues with NAD status.
Discussion:
In several places in 18.3.1.2 [numeric.limits.members], a member is described as "Meaningful for all floating point types." However, no clear method of determining a floating point type is provided.
In 18.3.1.5 [numeric.special], paragraph 1 states ". . . (for example, epsilon() is only meaningful if is_integer is false). . ." which suggests that a type is a floating point type if is_specialized is true and is_integer is false; however, this is unclear.
When clarifying this, please keep in mind this need of users: what exactly is the definition of floating point? Would a fixed point or rational representation be considered one? I guess my statement here is that there could also be types that are neither integer or (strictly) floating point.
Rationale:
It is up to the implementor of a user define type to decide if it is a floating point type.
Section: 22.4.1.3.2 [facet.ctype.char.members] Status: Dup Submitter: Robert Klarer Opened: 1999-11-02 Last modified: 2006-12-30
View all other issues in [facet.ctype.char.members].
View all issues with Dup status.
Duplicate of: 153
Discussion:
The widen and narrow member functions are described in 22.2.1.3.2, paragraphs 9-11. In each case we have two overloaded signatures followed by a Returns clause. The Returns clause only describes one of the overloads.
Proposed resolution:
Change the returns clause in 22.4.1.3.2 [facet.ctype.char.members] paragraph 10 from:
Returns: do_widen(low, high, to).
to:
Returns: do_widen(c) or do_widen(low, high, to), respectively.
Change the returns clause in 22.4.1.3.2 [facet.ctype.char.members] paragraph 11 from:
Returns: do_narrow(low, high, to).
to:
Returns: do_narrow(c) or do_narrow(low, high, to), respectively.
Rationale:
Subsumed by issue 153, which addresses the same paragraphs.
Section: 26.8 [c.math] Status: NAD Submitter: Nico Josuttis Opened: 2000-02-26 Last modified: 2006-12-29
View all other issues in [c.math].
View all issues with NAD status.
Discussion:
Due to the additional overloaded versions of numeric functions for float and long double according to Section 26.5, calls such as int x; std::pow (x, 4) are ambiguous now in a standard conforming implementation. Current implementations solve this problem very different (overload for all types, don't overload for float and long double, use preprocessor, follow the standard and get ambiguities).
This behavior should be standardized or at least identified as implementation defined.
Rationale:
These math issues are an understood and accepted consequence of the design. They have been discussed several times in the past. Users must write casts or write floating point expressions as arguments.
Section: 23.2.4 [associative.reqmts] Status: NAD Submitter: Judy Ward Opened: 2000-02-29 Last modified: 2006-12-27
View other active issues in [associative.reqmts].
View all other issues in [associative.reqmts].
View all issues with NAD status.
Discussion:
A user noticed that this doesn't compile with the Rogue Wave library because the rb_tree class declares a key_allocator, and allocator<const int> is not legal, I think:
map < const int, ... > // legal?
which made me wonder whether it is legal for a map's key_type to be const. In email from Matt Austern he said:
I'm not sure whether it's legal to declare a map with a const key type. I hadn't thought about that question until a couple weeks ago. My intuitive feeling is that it ought not to be allowed, and that the standard ought to say so. It does turn out to work in SGI's library, though, and someone in the compiler group even used it. Perhaps this deserves to be written up as an issue too.
Rationale:
The "key is assignable" requirement from table 69 in 23.2.4 [associative.reqmts] already implies the key cannot be const.
Section: 27.7.3 [std.manip] Status: Dup Submitter: Hyman Rosen Opened: 2000-02-29 Last modified: 2006-12-30
View all other issues in [std.manip].
View all issues with Dup status.
Duplicate of: 193
Discussion:
27.7.3 [std.manip] paragraph 5 says:
smanip setbase(int base);Returns: An object s of unspecified type such that if out is an (instance of) basic_ostream then the expression out<<s behaves as if f(s) were called, in is an (instance of) basic_istream then the expression in>>s behaves as if f(s) were called. Where f can be defined as:
ios_base& f(ios_base& str, int base) { // set basefield str.setf(n == 8 ? ios_base::oct : n == 10 ? ios_base::dec : n == 16 ? ios_base::hex : ios_base::fmtflags(0), ios_base::basefield); return str; }
There are two problems here. First, f takes two parameters, so the description needs to say that out<<s and in>>s behave as if f(s,base) had been called. Second, f is has a parameter named base, but is written as if the parameter was named n.
Actually, there's a third problem. The paragraph has grammatical errors. There needs to be an "and" after the first comma, and the "Where f" sentence fragment needs to be merged into its preceding sentence. You may also want to format the function a little better. The formatting above is more-or-less what the Standard contains.
Rationale:
The resolution of this defect is subsumed by the proposed resolution for issue 193.
[Tokyo: The LWG agrees that this is a defect and notes that it occurs additional places in the section, all requiring fixes.]
Section: 25.4 [alg.sorting] Status: NAD Submitter: Pablo Halpern Opened: 2000-03-06 Last modified: 2006-12-27
View all other issues in [alg.sorting].
View all issues with NAD status.
Discussion:
Many of the algorithms take an argument, pred, of template parameter type BinaryPredicate or an argument comp of template parameter type Compare. These algorithms usually have an overloaded version that does not take the predicate argument. In these cases pred is usually replaced by the use of operator== and comp is replaced by the use of operator<.
This use of hard-coded operators is inconsistent with other parts of the library, particularly the containers library, where equality is established using equal_to<> and ordering is established using less<>. Worse, the use of operator<, would cause the following innocent-looking code to have undefined behavior:
vector<string*> vec; sort(vec.begin(), vec.end());
The use of operator< is not defined for pointers to unrelated objects. If std::sort used less<> to compare elements, then the above code would be well-defined, since less<> is explicitly specialized to produce a total ordering of pointers.
Rationale:
This use of operator== and operator< was a very deliberate, conscious, and explicitly made design decision; these operators are often more efficient. The predicate forms are available for users who don't want to rely on operator== and operator<.
Section: 25.2.5 [alg.find] Status: NAD Submitter: Pablo Halpern Opened: 2000-03-06 Last modified: 2009-07-14
View all other issues in [alg.find].
View all issues with NAD status.
Discussion:
The find function always searches for a value using operator== to compare the value argument to each element in the input iterator range. This is inconsistent with other find-related functions such as find_end and find_first_of, which allow the caller to specify a binary predicate object to be used for determining equality. The fact that this can be accomplished using a combination of find_if and bind_1st or bind_2nd does not negate the desirability of a consistent, simple, alternative interface to find.
[ Summit: ]
Reopened by Alisdair.
[ 2009-07 Frankfurt ]
The same thing can be achieved using find_if (as noted in the issue).
Moved to NAD.
Proposed resolution:
In section 25.2.5 [alg.find], add a second prototype for find (between the existing prototype and the prototype for find_if), as follows:
template<class InputIterator, class T, class BinaryPredicate> InputIterator find(InputIterator first, InputIterator last, const T& value, BinaryPredicate bin_pred);Change the description of the return from:
Returns: The first iterator i in the range [first, last) for which the following corresponding conditions hold: *i == value, pred(*i) != false. Returns last if no such iterator is found.
to:
Returns: The first iterator i in the range [first, last) for which the following corresponding condition holds: *i == value, bin_pred(*i,value) != false, pred(*) != false. Return last if no such iterator is found.
Rationale:
This is request for a pure extension, so it is not a defect in the current standard. As the submitter pointed out, "this can be accomplished using a combination of find_if and bind_1st or bind_2nd".
Section: 22.4.1.3.2 [facet.ctype.char.members] Status: Dup Submitter: Dietmar Kühl Opened: 2000-04-24 Last modified: 2007-01-15
View all other issues in [facet.ctype.char.members].
View all issues with Dup status.
Duplicate of: 28
Discussion:
The description of the is() member in paragraph 4 of 22.4.1.3.2 [facet.ctype.char.members] is broken: According to this description, the second form of the is() method modifies the masks in the ctype object. The correct semantics if, of course, to obtain an array of masks. The corresponding method in the general case, ie. the do_is() method as described in 22.4.1.1.2 [locale.ctype.virtuals] paragraph 1 does the right thing.
Proposed resolution:
Change paragraph 4 from
The second form, for all *p in the range [low, high), assigns vec[p-low] to table()[(unsigned char)*p].
to become
The second form, for all *p in the range [low, high), assigns table()[(unsigned char)*p] to vec[p-low].
Rationale:
Section: 25.2.5 [alg.find] Status: NAD Submitter: Andrew Koenig Opened: 2000-05-02 Last modified: 2006-12-27
View all other issues in [alg.find].
View all issues with NAD status.
Discussion:
Is the following implementation of find acceptable?
template<class Iter, class X>
Iter find(Iter begin, Iter end, const X& x)
{
X x1 = x; // this is the crucial statement
while (begin != end && *begin != x1)
++begin;
return begin;
}
If the answer is yes, then it is implementation-dependent as to whether the following fragment is well formed:
vector<string> v;
find(v.begin(), v.end(), "foo");
At issue is whether there is a requirement that the third argument of find be CopyConstructible. There may be no problem here, but analysis is necessary.
Rationale:
There is no indication in the standard that find's third argument is required to be Copy Constructible. The LWG believes that no such requirement was intended. As noted above, there are times when a user might reasonably pass an argument that is not Copy Constructible.
Section: 24.6.1 [istream.iterator] Status: NAD Submitter: Andrew Koenig Opened: 2000-05-02 Last modified: 2006-12-27
View other active issues in [istream.iterator].
View all other issues in [istream.iterator].
View all issues with NAD status.
Discussion:
I do not think the standard specifies what operation(s) on istream iterators trigger input operations. So, for example:
istream_iterator<int> i(cin);
int n = *i++;
I do not think it is specified how many integers have been read from cin. The number must be at least 1, of course, but can it be 2? More?
Rationale:
The standard is clear as written: the stream is read every time operator++ is called, and it is also read either when the iterator is constructed or when operator* is called for the first time. In the example above, exactly two integers are read from cin.
There may be a problem with the interaction between istream_iterator and some STL algorithms, such as find. There are no guarantees about how many times find may invoke operator++.
Section: 23.2.4 [associative.reqmts] Status: Dup Submitter: Mark Rodgers Opened: 2000-05-19 Last modified: 2007-01-15
View other active issues in [associative.reqmts].
View all other issues in [associative.reqmts].
View all issues with Dup status.
Duplicate of: 233
Discussion:
Closed issue 192 raised several problems with the specification of this function, but was rejected as Not A Defect because it was too big a change with unacceptable impacts on existing implementations. However, issues remain that could be addressed with a smaller change and with little or no consequent impact.
The specification is inconsistent with the original proposal and with several implementations.
The initial implementation by Hewlett Packard only ever looked immediately before p, and I do not believe there was any intention to standardize anything other than this behavior. Consequently, current implementations by several leading implementors also look immediately before p, and will only insert after p in logarithmic time. I am only aware of one implementation that does actually look after p, and it looks before p as well. It is therefore doubtful that existing code would be relying on the behavior defined in the standard, and it would seem that fixing this defect as proposed below would standardize existing practice.
The specification is inconsistent with insertion for sequence containers.
This is difficult and confusing to teach to newcomers. All insert operations that specify an iterator as an insertion location should have a consistent meaning for the location represented by that iterator.
As specified, there is no way to hint that the insertion should occur at the beginning of the container, and the way to hint that it should occur at the end is long winded and unnatural.
For a container containing n elements, there are n+1 possible insertion locations and n+1 valid iterators. For there to be a one-to-one mapping between iterators and insertion locations, the iterator must represent an insertion location immediately before the iterator.
When appending sorted ranges using insert_iterators, insertions are guaranteed to be sub-optimal.
In such a situation, the optimum location for insertion is always immediately after the element previously inserted. The mechanics of the insert iterator guarantee that it will try and insert after the element after that, which will never be correct. However, if the container first tried to insert before the hint, all insertions would be performed in amortized constant time.
Proposed resolution:
In 23.1.2 [lib.associative.reqmts] paragraph 7, table 69, make the following changes in the row for a.insert(p,t):
assertion/note pre/post condition:
Change the last sentence from
"iterator p is a hint pointing to where the insert should start to search."
to
"iterator p is a hint indicating that immediately before p may be a correct location where the insertion could occur."
complexity:
Change the words "right after" to "immediately before".
Rationale:
Section: D.9.1 [auto.ptr] Status: NAD Submitter: Joseph Gottman Opened: 2000-06-30 Last modified: 2006-12-29
View all other issues in [auto.ptr].
View all issues with NAD status.
Discussion:
According to section 20.4.5, the function auto_ptr::operator=() returns a reference to an auto_ptr. The reason that operator=() usually returns a reference is to facilitate code like
int x,y,z;
x = y = z = 1;
However, given analogous code for auto_ptrs,
auto_ptr<int> x, y, z;
z.reset(new int(1));
x = y = z;
the result would be that z and y would both be set to NULL, instead of all the auto_ptrs being set to the same value. This makes such cascading assignments useless and counterintuitive for auto_ptrs.
Proposed resolution:
Change auto_ptr::operator=() to return void instead of an auto_ptr reference.
Rationale:
The return value has uses other than cascaded assignments: a user can call an auto_ptr member function, pass the auto_ptr to a function, etc. Removing the return value could break working user code.
Section: 27.6.2 [streambuf] Status: NAD Future Submitter: Martin Sebor Opened: 2000-08-12 Last modified: 2009-07-14
View all other issues in [streambuf].
View all issues with NAD Future status.
Discussion:
The basic_streambuf members gbump() and pbump() are specified to take an int argument. This requirement prevents the functions from effectively manipulating buffers larger than std::numeric_limits<int>::max() characters. It also makes the common use case for these functions somewhat difficult as many compilers will issue a warning when an argument of type larger than int (such as ptrdiff_t on LLP64 architectures) is passed to either of the function. Since it's often the result of the subtraction of two pointers that is passed to the functions, a cast is necessary to silence such warnings. Finally, the usage of a native type in the functions signatures is inconsistent with other member functions (such as sgetn() and sputn()) that manipulate the underlying character buffer. Those functions take a streamsize argument.
[ 2009-07 Frankfurt ]
This is part of a bigger problem. If anyone cares enough, they should write a paper solving the bigger problem of offset types in iostreams.
This is related to the paper about large file sizes. Beman has already agreed to drop the section of that paper that deals with this.
int is big enough for reasonable buffers.
Move to NAD Future.
This is related to LWG 423.
Proposed resolution:
Change the signatures of these functions in the synopsis of template class basic_streambuf (27.5.2) and in their descriptions (27.5.2.3.1, p4 and 27.5.2.3.2, p4) to take a streamsize argument.
Although this change has the potential of changing the ABI of the library, the change will affect only platforms where int is different than the definition of streamsize. However, since both functions are typically inline (they are on all known implementations), even on such platforms the change will not affect any user code unless it explicitly relies on the existing type of the functions (e.g., by taking their address). Such a possibility is IMO quite remote.
Alternate Suggestion from Howard Hinnant, c++std-lib-7780:
This is something of a nit, but I'm wondering if streamoff wouldn't be a better choice than streamsize. The argument to pbump and gbump MUST be signed. But the standard has this to say about streamsize (27.4.1/2/Footnote):
[Footnote: streamsize is used in most places where ISO C would use size_t. Most of the uses of streamsize could use size_t, except for the strstreambuf constructors, which require negative values. It should probably be the signed type corresponding to size_t (which is what Posix.2 calls ssize_t). --- end footnote]
This seems a little weak for the argument to pbump and gbump. Should we ever really get rid of strstream, this footnote might go with it, along with the reason to make streamsize signed.
Rationale:
The LWG believes this change is too big for now. We may wish to reconsider this for a future revision of the standard. One possibility is overloading pbump, rather than changing the signature.
[ [2006-05-04: Reopened at the request of Chris (Krzysztof ?elechowski)] ]
Section: 20.7.3 [base], 24.4.2 [iterator.basic] Status: NAD Submitter: Robert Dick Opened: 2000-08-17 Last modified: 2006-12-29
View all other issues in [base].
View all issues with NAD status.
Discussion:
According to the November 1997 Draft Standard, the results of deleting an object of a derived class through a pointer to an object of its base class are undefined if the base class has a non-virtual destructor. Therefore, it is potentially dangerous to publicly inherit from such base classes.
Defect:
The STL design encourages users to publicly inherit from a number of classes
which do nothing but specify interfaces, and which contain non-virtual
destructors.
Attribution:
Wil Evers and William E. Kempf suggested this modification for functional
objects.
Proposed resolution:
When a base class in the standard library is useful only as an interface specifier, i.e., when an object of the class will never be directly instantiated, specify that the class contains a protected destructor. This will prevent deletion through a pointer to the base class without performance, or space penalties (on any implementation I'm aware of).
As an example, replace...
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
};
... with...
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
protected:
~unary_function() {}
};
Affected definitions:
20.3.1 [lib.function.objects] -- unary_function, binary_function
24.3.2 [lib.iterator.basic] -- iterator
Rationale:
The standard is clear as written; this is a request for change, not a defect in the strict sense. The LWG had several different objections to the proposed change. One is that it would prevent users from creating objects of type unary_function and binary_function. Doing so can sometimes be legitimate, if users want to pass temporaries as traits or tag types in generic code.
Section: D.7.1.3 [depr.strstreambuf.virtuals] Status: NAD Submitter: Martin Sebor Opened: 2000-10-05 Last modified: 2007-01-15
View all other issues in [depr.strstreambuf.virtuals].
View all issues with NAD status.
Discussion:
It appears that the interaction of the strstreambuf members overflow() and seekoff() can lead to undefined behavior in cases where defined behavior could reasonably be expected. The following program demonstrates this behavior:
#include <strstream>
int main ()
{
std::strstreambuf sb;
sb.sputc ('c');
sb.pubseekoff (-1, std::ios::end, std::ios::in);
return !('c' == sb.sgetc ());
}
D.7.1.1, p1 initializes strstreambuf with a call to basic_streambuf<>(), which in turn sets all pointers to 0 in 27.5.2.1, p1.
27.5.2.2.5, p1 says that basic_streambuf<>::sputc(c) calls overflow(traits::to_int_type(c)) if a write position isn't available (it isn't due to the above).
D.7.1.3, p3 says that strstreambuf::overflow(off, ..., ios::in) makes at least one write position available (i.e., it allows the function to make any positive number of write positions available).
D.7.1.3, p13 computes newoff = seekhigh - eback(). In D.7.1, p4 we see seekhigh = epptr() ? epptr() : egptr(), or seekhigh = epptr() in this case. newoff is then epptr() - eback().
D.7.1.4, p14 sets gptr() so that gptr() == eback() + newoff + off, or gptr() == epptr() + off holds.
If strstreambuf::overflow() made exactly one write position available then gptr() will be set to just before epptr(), and the program will return 0. Buf if the function made more than one write position available, epptr() and gptr() will both point past pptr() and the behavior of the program is undefined.
Proposed resolution:
Change the last sentence of D.7.1 [depr.strstreambuf] paragraph 4 from
Otherwise, seeklow equals gbeg and seekhigh is either pend, if pend is not a null pointer, or gend.
to become
Otherwise, seeklow equals gbeg and seekhigh is either gend if 0 == pptr(), or pbase() + max where max is the maximum value of pptr() - pbase() ever reached for this stream.
[ pre-Copenhagen: Dietmar provided wording for proposed resolution. ]
[ post-Copenhagen: Fixed a typo: proposed resolution said to fix 4.7.1, not D.7.1. ]
Rationale:
This is related to issue 65: it's not clear what it means to seek beyond the current area. Without resolving issue 65 we can't resolve this. As with issue 65, the library working group does not wish to invest time nailing down corner cases in a deprecated feature.
Section: 18.8 [support.exception] Status: NAD Submitter: J. Stephen Adamczyk Opened: 2000-10-10 Last modified: 2006-12-27
View all other issues in [support.exception].
View all issues with NAD status.
Discussion:
One of our customers asks whether this is valid C++:
#include <cstdarg>
void bar(const char *, va_list);
void
foo(const char *file, const char *, ...)
{
va_list ap;
va_start(ap, file);
bar(file, ap);
va_end(ap);
}
The issue being whether it is valid to use cstdarg when the final parameter before the "..." is unnamed. cstdarg is, as far as I can tell, inherited verbatim from the C standard. and the definition there (7.8.1.1 in the ISO C89 standard) refers to "the identifier of the rightmost parameter". What happens when there is no such identifier?
My personal opinion is that this should be allowed, but some tweak might be required in the C++ standard.
Rationale:
Not a defect, the C and C++ standards are clear. It is impossible to use varargs if the parameter immediately before "..." has no name, because that is the parameter that must be passed to va_start. The example given above is broken, because va_start is being passed the wrong parameter.
There is no support for extending varargs to provide additional functionality beyond what's currently there. For reasons of C/C++ compatibility, it is especially important not to make gratuitous changes in this part of the C++ standard. The C committee has already been requested not to touch this part of the C standard unless necessary.
Section: 20.2.2 [allocator.requirements] Status: NAD Submitter: Matt Austern Opened: 2000-11-07 Last modified: 2006-12-30
View other active issues in [allocator.requirements].
View all other issues in [allocator.requirements].
View all issues with NAD status.
Discussion:
In 20.1.5, paragraph 5, the standard says that "Implementors are encouraged to supply libraries that can accept allocators that encapsulate more general memory models and that support non-equal instances." This is intended as normative encouragement to standard library implementors. However, it is possible to interpret this sentence as applying to nonstandard third-party libraries.
Proposed resolution:
In 20.1.5, paragraph 5, change "Implementors" to "Implementors of the library described in this International Standard".
Rationale:
The LWG believes the normative encouragement is already sufficiently clear, and that there are no important consequences even if it is misunderstood.
Section: 23.2 [container.requirements] Status: NAD Submitter: Steve Cleary Opened: 2000-11-27 Last modified: 2006-12-27
View other active issues in [container.requirements].
View all other issues in [container.requirements].
View all issues with NAD status.
Discussion:
This came from an email from Steve Cleary to Fergus in reference to issue 179. The library working group briefly discussed this in Toronto and believes it should be a separate issue.
Steve said: "We may want to state that the const/non-const iterators must have the same difference type, size_type, and category."
(Comment from Judy) I'm not sure if the above sentence should be true for all const and non-const iterators in a particular container, or if it means the container's iterator can't be compared with the container's const_iterator unless the above it true. I suspect the former.
Proposed resolution:
In Section: 23.2 [container.requirements], table 65, in the assertion/note pre/post condition for X::const_iterator, add the following:
typeid(X::const_iterator::difference_type) == typeid(X::iterator::difference_type)
typeid(X::const_iterator::size_type) == typeid(X::iterator::size_type)
typeid(X::const_iterator::category) == typeid(X::iterator::category)
Rationale:
Going through the types one by one: Iterators don't have a size_type. We already know that the difference types are identical, because the container requirements already say that the difference types of both X::iterator and X::const_iterator are both X::difference_type. The standard does not require that X::iterator and X::const_iterator have the same iterator category, but the LWG does not see this as a defect: it's possible to imagine cases in which it would be useful for the categories to be different.
It may be desirable to require X::iterator and X::const_iterator to have the same value type, but that is a new issue. (Issue 322.)
Section: 27.5.2.2 [fmtflags.state] Status: NAD Submitter: Judy Ward Opened: 2000-12-30 Last modified: 2006-12-27
View all other issues in [fmtflags.state].
View all issues with NAD status.
Discussion:
The Effects clause for ios_base::setf(fmtflags fmtfl) says "Sets fmtfl in flags()". What happens if the user first calls ios_base::scientific and then calls ios_base::fixed or vice-versa? This is an issue for all of the conflicting flags, i.e. ios_base::left and ios_base::right or ios_base::dec, ios_base::hex and ios_base::oct.
I see three possible solutions:
Most existing implementations that I tried seem to conform to resolution #3, except that when using the iomanip manipulator hex or oct then that always overrides dec, but calling setf(ios_base::hex) doesn't.
There is a sort of related issue, which is that although the ios_base constructor says that each ios_base member has an indeterminate value after construction, all the existing implementations I tried explicitly set ios_base::dec.
Proposed resolution:
Rationale:
adjustfield, basefield, and floatfield are each multi-bit fields. It is possible to set multiple bits within each of those fields. (For example, dec and oct). These fields are used by locale facets. The LWG reviewed the way in which each of those three fields is used, and believes that in each case the behavior is well defined for any possible combination of bits. See for example Table 58, in 22.4.2.2.2 [facet.num.put.virtuals], noting the requirement in paragraph 6 of that section.
Users are advised to use manipulators, or else use the two-argument version of setf, to avoid unexpected behavior.
Section: 26.8 [c.math] Status: NAD Submitter: Judy Ward Opened: 2000-12-30 Last modified: 2007-01-15
View all other issues in [c.math].
View all issues with NAD status.
Discussion:
In ISO/IEC 9899:1990 Programming Languages C we find the following concerning <math.h>:
7.13.4 Mathematics <math.h>
The names of all existing functions declared in the <math.h> header, suffixed with f or l, are reserved respectively for corresponding functions with float and long double arguments are return values.
For example, float sinf(float) is reserved.
In the C99 standard, <math.h> must contain declarations for these functions.
So, is it acceptable for an implementor to add these prototypes to the C++ versions of the math headers? Are they required?
Proposed resolution:
Add these Functions to Table 80, section 26.5 and to Table 99, section C.2:
acosf asinf atanf atan2f ceilf cosf coshf
expf fabsf floorf fmodf frexpf ldexpf
logf log10f modff powf sinf sinhf sqrtf
tanf tanhf
acosl asinl atanl atan2l ceill cosl coshl
expl fabsl floorl fmodl frexpl ldexpl
logl log10l modfl powl sinl sinhl sqrtl
tanl tanhl
There should probably be a note saying that these functions are optional and, if supplied, should match the description in the 1999 version of the C standard. In the next round of C++ standardization they can then become mandatory.
Rationale:
The C90 standard, as amended, already permits (but does not require) these functions, and the C++ standard incorporates the C90 standard by reference. C99 is not an issue, because it is never referred to by the C++ standard.
Section: 25.2.4 [alg.foreach] Status: NAD Submitter: Angelika Langer Opened: 2001-01-03 Last modified: 2009-07-14
View all other issues in [alg.foreach].
View all issues with NAD status.
Discussion:
The specification of the for_each algorithm does not have a "Requires" section, which means that there are no restrictions imposed on the function object whatsoever. In essence it means that I can provide any function object with arbitrary side effects and I can still expect a predictable result. In particular I can expect that the function object is applied exactly last - first times, which is promised in the "Complexity" section.
I don't see how any implementation can give such a guarantee without imposing requirements on the function object.
Just as an example: consider a function object that removes elements from the input sequence. In that case, what does the complexity guarantee (applies f exactly last - first times) mean?
One can argue that this is obviously a nonsensical application and a theoretical case, which unfortunately it isn't. I have seen programmers shooting themselves in the foot this way, and they did not understand that there are restrictions even if the description of the algorithm does not say so.
[Lillehammer: This is more general than for_each. We don't want the function object in transform invalidiating iterators either. There should be a note somewhere in clause 17 (17, not 25) saying that user code operating on a range may not invalidate iterators unless otherwise specified. Bill will provide wording.]
[ 2009-07 Frankfurt ]
Moved to NAD.
It was felt that the current description is adequate, and that there are limits to what the standard can reasonably say to prohibit perverse uses of the library.
Proposed resolution:
Section: 25.3.4 [alg.transform] Status: NAD Submitter: Angelika Langer Opened: 2001-01-04 Last modified: 2007-01-15
View all other issues in [alg.transform].
View all issues with NAD status.
Discussion:
This issue is related to issue 242. In case that the resolution proposed for issue 242 is accepted, we have have the following situation: The 4 numeric algorithms (accumulate and consorts) as well as transform would allow a certain category of side effects. The numeric algorithms specify that they invoke the functor "for every iterator i in the range [first, last) in order". transform, in contrast, would not give any guarantee regarding order of invocation of the functor, which means that the functor can be invoked in any arbitrary order.
Why would that be a problem? Consider an example: say the transformator that is a simple enumerator ( or more generally speaking, "is order-sensitive" ). Since a standard compliant implementation of transform is free to invoke the enumerator in no definite order, the result could be a garbled enumeration. Strictly speaking this is not a problem, but it is certainly at odds with the prevalent understanding of transform as an algorithms that assigns "a new _corresponding_ value" to the output elements.
All implementations that I know of invoke the transformator in definite order, namely starting from first and proceeding to last - 1. Unless there is an optimization conceivable that takes advantage of the indefinite order I would suggest to specify the order, because it eliminate the uncertainty that users would otherwise have regarding the order of execution of their potentially order-sensitive function objects.
Proposed resolution:
In section 25.2.3 - Transform [lib.alg.transform] change:
-1- Effects: Assigns through every iterator i in the range [result, result + (last1 - first1)) a new corresponding value equal to op(*(first1 + (i - result)) or binary_op(*(first1 + (i - result), *(first2 + (i - result))).
to:
-1- Effects: Computes values by invoking the operation op or binary_op for every iterator in the range [first1, last1) in order. Assigns through every iterator i in the range [result, result + (last1 - first1)) a new corresponding value equal to op(*(first1 + (i - result)) or binary_op(*(first1 + (i - result), *(first2 + (i - result))).
Rationale:
For Input Iterators an order is already guaranteed, because only one order is possible. If a user who passes a Forward Iterator to one of these algorithms really needs a specific order of execution, it's possible to achieve that effect by wrapping it in an Input Iterator adaptor.
Section: 22.4.1.5 [locale.codecvt.byname] Status: NAD Submitter: Gregory Bumgardner Opened: 2001-01-25 Last modified: 2006-12-27
View all other issues in [locale.codecvt.byname].
View all issues with NAD status.
Discussion:
The effects of codecvt<>::do_length() are described in 22.2.1.5.2, paragraph 10. As implied by that paragraph, and clarified in issue 75, codecvt<>::do_length() must process the source data and update the stateT argument just as if the data had been processed by codecvt<>::in(). However, the standard does not specify how do_length() would report a translation failure, should the source sequence contain untranslatable or illegal character sequences.
The other conversion methods return an "error" result value to indicate that an untranslatable character has been encountered, but do_length() already has a return value (the number of source characters that have been processed by the method).
Proposed resolution:
This issue cannot be resolved without modifying the interface. An exception cannot be used, as there would be no way to determine how many characters have been processed and the state object would be left in an indeterminate state.
A source compatible solution involves adding a fifth argument to length() and do_length() that could be used to return position of the offending character sequence. This argument would have a default value that would allow it to be ignored:
int length(stateT& state,
const externT* from,
const externT* from_end,
size_t max,
const externT** from_next = 0);
virtual
int do_length(stateT& state,
const externT* from,
const externT* from_end,
size_t max,
const externT** from_next);
Then an exception could be used to report any translation errors and the from_next argument, if used, could then be used to retrieve the location of the offending character sequence.
Rationale:
The standard is already clear: the return value is the number of "valid complete characters". If it encounters an invalid sequence of external characters, it stops.
Section: X [iterator.concepts] Status: NAD Submitter: Dave Abrahams Opened: 2001-02-05 Last modified: 2008-09-30
View other active issues in [iterator.concepts].
View all other issues in [iterator.concepts].
View all issues with NAD status.
Discussion:
We all "know" that input iterators are allowed to produce values when dereferenced of which there is no other in-memory copy.
But: Table 72, with a careful reading, seems to imply that this can only be the case if the value_type has no members (e.g. is a built-in type).
The problem occurs in the following entry:
a->m pre: (*a).m is well-defined
Equivalent to (*a).m
*a.m can be well-defined if *a is not a reference type, but since operator->() must return a pointer for a->m to be well-formed, it needs something to return a pointer to. This seems to indicate that *a must be buffered somewhere to make a legal input iterator.
I don't think this was intentional.
Rationale:
The current standard is clear and consistent. Input iterators that return rvalues are in fact implementable. They may in some cases require extra work, but it is still possible to define an operator-> in such cases: it doesn't have to return a T*, but may return a proxy type. No change to the standard is justified.
Section: 27.7 [iostream.format] Status: NAD Submitter: Martin Sebor Opened: 2001-03-19 Last modified: 2009-07-14
View all other issues in [iostream.format].
View all issues with NAD status.
Discussion:
The descriptions of the constructors of basic_istream<>::sentry (27.7.1.1.3 [istream::sentry]) and basic_ostream<>::sentry (27.7.2.4 [ostream::sentry]) do not explain what the functions do in case an exception is thrown while they execute. Some current implementations allow all exceptions to propagate, others catch them and set ios_base::badbit instead, still others catch some but let others propagate.
The text also mentions that the functions may call setstate(failbit) (without actually saying on what object, but presumably the stream argument is meant). That may have been fine for basic_istream<>::sentry prior to issue 195, since the function performs an input operation which may fail. However, issue 195 amends 27.7.1.1.3 [istream::sentry], p2 to clarify that the function should actually call setstate(failbit | eofbit), so the sentence in p3 is redundant or even somewhat contradictory.
The same sentence that appears in 27.7.2.4 [ostream::sentry], p3 doesn't seem to be very meaningful for basic_istream<>::sentry which performs no input. It is actually rather misleading since it would appear to guide library implementers to calling setstate(failbit) when os.tie()->flush(), the only called function, throws an exception (typically, it's badbit that's set in response to such an event).
Additional comments from Martin, who isn't comfortable with the current proposed resolution (see c++std-lib-11530)
The istream::sentry ctor says nothing about how the function deals with exemptions (27.6.1.1.2, p1 says that the class is responsible for doing "exception safe"(*) prefix and suffix operations but it doesn't explain what level of exception safety the class promises to provide). The mockup example of a "typical implementation of the sentry ctor" given in 27.6.1.1.2, p6, removed in ISO/IEC 14882:2003, doesn't show exception handling, either. Since the ctor is not classified as a formatted or unformatted input function, the text in 27.6.1.1, p1 through p4 does not apply. All this would seem to suggest that the sentry ctor should not catch or in any way handle exceptions thrown from any functions it may call. Thus, the typical implementation of an istream extractor may look something like [1].
The problem with [1] is that while it correctly sets ios::badbit if an exception is thrown from one of the functions called from the sentry ctor, if the sentry ctor reaches EOF while extracting whitespace from a stream that has eofbit or failbit set in exceptions(), it will cause an ios::failure to be thrown, which will in turn cause the extractor to set ios::badbit.
The only straightforward way to prevent this behavior is to move the definition of the sentry object in the extractor above the try block (as suggested by the example in 22.2.8, p9 and also indirectly supported by 27.6.1.3, p1). See [2]. But such an implementation will allow exceptions thrown from functions called from the ctor to freely propagate to the caller regardless of the setting of ios::badbit in the stream object's exceptions().
So since neither [1] nor [2] behaves as expected, the only possible solution is to have the sentry ctor catch exceptions thrown from called functions, set badbit, and propagate those exceptions if badbit is also set in exceptions(). (Another solution exists that deals with both kinds of sentries, but the code is non-obvious and cumbersome -- see [3].)
Please note that, as the issue points out, current libraries do not behave consistently, suggesting that implementors are not quite clear on the exception handling in istream::sentry, despite the fact that some LWG members might feel otherwise. (As documented by the parenthetical comment here: http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1480.html#309)
Also please note that those LWG members who in Copenhagen felt that "a sentry's constructor should not catch exceptions, because sentries should only be used within (un)formatted input functions and that exception handling is the responsibility of those functions, not of the sentries," as noted here http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2001/n1310.html#309 would in effect be either arguing for the behavior described in [1] or for extractors implemented along the lines of [3].
The original proposed resolution (Revision 25 of the issues list) clarifies the role of the sentry ctor WRT exception handling by making it clear that extractors (both library or user-defined) should be implemented along the lines of [2] (as opposed to [1]) and that no exception thrown from the callees should propagate out of either function unless badbit is also set in exceptions().
[1] Extractor that catches exceptions thrown from sentry:
struct S { long i; };
istream& operator>> (istream &strm, S &s)
{
ios::iostate err = ios::goodbit;
try {
const istream::sentry guard (strm, false);
if (guard) {
use_facet<num_get<char> >(strm.getloc ())
.get (istreambuf_iterator<char>(strm),
istreambuf_iterator<char>(),
strm, err, s.i);
}
}
catch (...) {
bool rethrow;
try {
strm.setstate (ios::badbit);
rethrow = false;
}
catch (...) {
rethrow = true;
}
if (rethrow)
throw;
}
if (err)
strm.setstate (err);
return strm;
}
[2] Extractor that propagates exceptions thrown from sentry:
istream& operator>> (istream &strm, S &s)
{
istream::sentry guard (strm, false);
if (guard) {
ios::iostate err = ios::goodbit;
try {
use_facet<num_get<char> >(strm.getloc ())
.get (istreambuf_iterator<char>(strm),
istreambuf_iterator<char>(),
strm, err, s.i);
}
catch (...) {
bool rethrow;
try {
strm.setstate (ios::badbit);
rethrow = false;
}
catch (...) {
rethrow = true;
}
if (rethrow)
throw;
}
if (err)
strm.setstate (err);
}
return strm;
}
[3] Extractor that catches exceptions thrown from sentry but doesn't set badbit if the exception was thrown as a result of a call to strm.clear().
istream& operator>> (istream &strm, S &s)
{
const ios::iostate state = strm.rdstate ();
const ios::iostate except = strm.exceptions ();
ios::iostate err = std::ios::goodbit;
bool thrown = true;
try {
const istream::sentry guard (strm, false);
thrown = false;
if (guard) {
use_facet<num_get<char> >(strm.getloc ())
.get (istreambuf_iterator<char>(strm),
istreambuf_iterator<char>(),
strm, err, s.i);
}
}
catch (...) {
if (thrown && state & except)
throw;
try {
strm.setstate (ios::badbit);
thrown = false;
}
catch (...) {
thrown = true;
}
if (thrown)
throw;
}
if (err)
strm.setstate (err);
return strm;
}
[Pre-Berlin] Reopened at the request of Paolo Carlini and Steve Clamage.
[Pre-Portland] A relevant newsgroup post:
The current proposed resolution of issue #309 (http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#309) is unacceptable. I write commerical software and coding around this makes my code ugly, non-intuitive, and requires comments referring people to this very issue. Following is the full explanation of my experience.
In the course of writing software for commercial use, I constructed std::ifstream's based on user-supplied pathnames on typical POSIX systems.
It was expected that some files that opened successfully might not read successfully -- such as a pathname which actually refered to a directory. Intuitively, I expected the streambuffer underflow() code to throw an exception in this situation, and recent implementations of libstdc++'s basic_filebuf do just that (as well as many of my own custom streambufs).
I also intuitively expected that the istream code would convert these exceptions to the "badbit' set on the stream object, because I had not requested exceptions. I refer to 27.6.1.1. P4.
However, this was not the case on at least two implementations -- if the first thing I did with an istream was call operator>>( T& ) for T among the basic arithmetic types and std::string. Looking further I found that the sentry's constructor was invoking the exception when it pre-scanned for whitespace, and the extractor function (operator>>()) was not catching exceptions in this situation.
So, I was in a situation where setting 'noskipws' would change the istream's behavior even though no characters (whitespace or not) could ever be successfully read.
Also, calling .peek() on the istream before calling the extractor() changed the behavior (.peek() had the effect of setting the badbit ahead of time).
I found this all to be so inconsistent and inconvenient for me and my code design, that I filed a bugzilla entry for libstdc++. I was then told that the bug cannot be fixed until issue #309 is resolved by the committee.
[ 2009-07 Frankfurt ]
Moved to NAD.
See the rationale in the issue. Paolo, who requested that the issue be reopened, agreed with the rationale.
Proposed resolution:
Rationale:
The LWG agrees there is minor variation between implementations, but believes that it doesn't matter. This is a rarely used corner case. There is no evidence that this has any commercial importance or that it causes actual portability problems for customers trying to write code that runs on multiple implementations.
Section: 18.8.3.3 [terminate] Status: NAD Submitter: Judy Ward Opened: 2001-04-03 Last modified: 2006-12-27
View all other issues in [terminate].
View all issues with NAD status.
Discussion:
According to section 18.7.3.3 of the standard, std::terminate() is supposed to call the terminate_handler in effect immediately after evaluating the throw expression.
Question: what if the terminate_handler in effect is itself std::terminate?
For example:
#include <exception>
int main () {
std::set_terminate(std::terminate);
throw 5;
return 0;
}
Is the implementation allowed to go into an infinite loop?
I think the same issue applies to std::set_unexpected.
Proposed resolution:
Rationale:
Infinite recursion is to be expected: users who set the terminate handler to terminate are explicitly asking for terminate to call itself.
Section: 18.8.3.3 [terminate] Status: NAD Submitter: Detlef Vollmann Opened: 2001-04-11 Last modified: 2007-01-15
View all other issues in [terminate].
View all issues with NAD status.
Discussion:
The standard appears to contradict itself about whether the stack is unwound when the implementation calls terminate().
From 18.7.3.3p2:
Calls the terminate_handler function in effect immediately after evaluating the throw-expression (lib.terminate.handler), if called by the implementation [...]
So the stack is guaranteed not to be unwound.
But from 15.3p9:
[...]whether or not the stack is unwound before this call to terminate() is implementation-defined (except.terminate).
And 15.5.1 actually defines that in most cases the stack is unwound.
Proposed resolution:
Rationale:
There is definitely no contradiction between the core and library clauses; nothing in the core clauses says that stack unwinding happens after terminate is called. 18.7.3.3p2 does not say anything about when terminate() is called; it merely specifies which terminate_handler is used.
Section: 26.8 [c.math] Status: NAD Submitter: Dave Abrahams Opened: 2001-06-04 Last modified: 2008-03-12
View all other issues in [c.math].
View all issues with NAD status.
Discussion:
Currently the standard mandates the following overloads of abs():
abs(long), abs(int) in <cstdlib>
abs(float), abs(double), abs(long double) in <cmath>
template<class T> T abs(const complex<T>&) in <complex>
template<class T> valarray<T> abs(const valarray<T>&); in <valarray>
The problem is that having only some overloads visible of a function that works on "implicitly inter-convertible" types is dangerous in practice. The headers that get included at any point in a translation unit can change unpredictably during program development/maintenance. The wrong overload might be unintentionally selected.
Currently, there is nothing that mandates the simultaneous visibility of these overloads. Indeed, some vendors have begun fastidiously reducing dependencies among their (public) headers as a QOI issue: it helps people to write portable code by refusing to compile unless all the correct headers are #included.
The same issue may exist for other functions in the library.
Redmond: PJP reports that C99 adds two new kinds of abs: complex, and int_max_abs.
Related issue: 343.
[ Bellevue: ]
The situation is not sufficiently severe to warrant a change.
Rationale:
The programs that could potentially be broken by this situation are already fragile, and somewhat contrived: For example, a user-defined class that has conversion overloads both to long and to float. If x is a value of such a class, then abs(x) would give the long version if the user included <cstdlib>, the float version if the user included <cmath>, and would be diagnosed as ambiguous at compile time if the user included both headers. The LWG couldn't find an example of a program whose meaning would be changed (as opposed to changing it from well-formed to ill-formed) simply by adding another standard header.
Since the harm seems minimal, and there don't seem to be any simple and noninvasive solutions, this is being closed as NAD. It is marked as "Future" for two reasons. First, it might be useful to define an <all> header that would include all Standard Library headers. Second, we should at least make sure that future library extensions don't make this problem worse.
Section: 22.4.6.4 [locale.moneypunct.byname] Status: NAD Submitter: Martin Sebor Opened: 2001-07-05 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
The definition of the moneypunct facet contains the typedefs char_type and string_type. Only one of these names, string_type, is defined in the derived facet, moneypunct_byname.
Proposed resolution:
For consistency with the numpunct facet, add a typedef for char_type to the definition of the moneypunct_byname facet in 22.4.6.4 [locale.moneypunct.byname].
Rationale:
The absence of the typedef is irrelevant. Users can still access the typedef, because it is inherited from the base class.
Section: 22.3.1 [locale] Status: NAD Submitter: Martin Sebor Opened: 2001-07-15 Last modified: 2006-12-27
View all other issues in [locale].
View all issues with NAD status.
Discussion:
The "exposition only" value of the std::locale::none constant shown in the definition of class locale is misleading in that it on many systems conflicts with the value assigned to one if the LC_XXX constants (specifically, LC_COLLATE on AIX, LC_ALL on HP-UX, LC_CTYPE on Linux and SunOS). This causes incorrect behavior when such a constant is passed to one of the locale member functions that accept a locale::category argument and interpret it as either the C LC_XXX constant or a bitmap of locale::category values. At least three major implementations adopt the suggested value without a change and consequently suffer from this problem.
For instance, the following code will (presumably) incorrectly copy facets belonging to the collate category from the German locale on AIX:
std::locale l (std::locale ("C"), "de_DE", std::locale::none);
Rationale:
The LWG agrees that it may be difficult to implement locale member functions in such a way that they can take either category arguments or the LC_ constants defined in <cctype>. In light of this requirement (22.3.1.1.1 [locale.category], paragraph 2), and in light of the requirement in the preceding paragraph that it is possible to combine category bitmask elements with bitwise operations, defining the category elements is delicate, particularly if an implementor is constrained to work with a preexisting C library. (Just using the existing LC_ constants would not work in general.) There's no set of "exposition only" values that could give library implementors proper guidance in such a delicate matter. The non-normative example we're giving is no worse than any other choice would be.
See issue 347.
Section: 27.5.3 [fpos] Status: NAD Submitter: PremAnand M. Rao Opened: 2001-08-27 Last modified: 2006-12-27
View all other issues in [fpos].
View all issues with NAD status.
Discussion:
Increment and decrement operators are missing from Table 88 -- Position type requirements in 27.5.3 [fpos].
Proposed resolution:
Table 88 (section 27.4.3) -- Position type requirements be updated to include increment and decrement operators.
expression return type operational note
++p fpos& p += O(1)
p++ fpos { P tmp = p;
++p;
return tmp; }
--p fpos& p -= O(1)
p-- fpos { P tmp = p;
--p;
return tmp; }
Rationale:
The LWG believes this is a request for extension, not a defect report. Additionally, nobody saw a clear need for this extension; fpos is used only in very limited ways.
Section: 27.7.1.3 [istream.unformatted] Status: NAD Submitter: Howard Hinnant Opened: 2001-10-09 Last modified: 2009-07-14
View all other issues in [istream.unformatted].
View all issues with NAD status.
Discussion:
I think we have a defect.
According to lwg issue 60 which is now a dr, the description of seekg in 27.7.1.3 [istream.unformatted] paragraph 38 now looks like:
Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekpos( pos).
And according to lwg issue 243 which is also now a dr, 27.6.1.3, paragraph 1 looks like:
Each unformatted input function begins execution by constructing an object of class sentry with the default argument noskipws (second) argument true. If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input. Otherwise, if the sentry constructor exits by throwing an exception or if the sentry object returns false, when converted to a value of type bool, the function returns without attempting to obtain any input. In either case the number of extracted characters is set to 0; unformatted input functions taking a character array of non-zero size as an argument shall also store a null character (using charT()) in the first location of the array. If an exception is thrown during input then ios::badbit is turned on in *this'ss error state. If (exception()&badbit)!= 0 then the exception is rethrown. It also counts the number of characters extracted. If no exception has been thrown it ends by storing the count in a member object and returning the value specified. In any event the sentry object is destroyed before leaving the unformatted input function.
And finally 27.6.1.1.2/5 says this about sentry:
If, after any preparation is completed, is.good() is true, ok_ != false otherwise, ok_ == false.
So although the seekg paragraph says that the operation proceeds if !fail(), the behavior of unformatted functions says the operation proceeds only if good(). The two statements are contradictory when only eofbit is set. I don't think the current text is clear which condition should be respected.
Further discussion from Redmond:
PJP: It doesn't seem quite right to say that seekg is "unformatted". That makes specific claims about sentry that aren't quite appropriate for seeking, which has less fragile failure modes than actual input. If we do really mean that it's unformatted input, it should behave the same way as other unformatted input. On the other hand, "principle of least surprise" is that seeking from EOF ought to be OK.
Pre-Berlin: Paolo points out several problems with the proposed resolution in Ready state:
[ 2009-07 Frankfurt ]
Moved to NAD. Will reopen if proposed resolution is supplied.
Proposed resolution:
Change 27.7.1.3 [istream.unformatted] to:
Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1), except that it does not count the number of characters extracted, does not affect the value returned by subsequent calls to gcount(), and does not examine the value returned by the sentry object. After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekpos(pos). In case of success, the function calls clear(). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).
[Lillehammer: Matt provided wording.]
Rationale:
In C, fseek does clear EOF. This is probably what most users would expect. We agree that having eofbit set should not deter a seek, and that a successful seek should clear eofbit. Note that fail() is true only if failbit or badbit is set, so using !fail(), rather than good(), satisfies this goal.
Section: 17 [library] Status: NAD Submitter: Martin Sebor Opened: 2001-10-09 Last modified: 2009-07-28
View other active issues in [library].
View all other issues in [library].
View all issues with NAD status.
Discussion:
The synopses of the C++ library headers clearly show which names are required to be defined in each header. Since in order to implement the classes and templates defined in these headers declarations of other templates (but not necessarily their definitions) are typically necessary the standard in 17.4.4, p1 permits library implementers to include any headers needed to implement the definitions in each header.
For instance, although it is not explicitly specified in the synopsis of <string>, at the point of definition of the std::basic_string template the declaration of the std::allocator template must be in scope. All current implementations simply include <memory> from within <string>, either directly or indirectly, to bring the declaration of std::allocator into scope.
Additionally, however, some implementation also include <istream> and <ostream> at the top of <string> to bring the declarations of std::basic_istream and std::basic_ostream into scope (which are needed in order to implement the string inserter and extractor operators (21.3.7.9 [lib.string.io])). Other implementations only include <iosfwd>, since strictly speaking, only the declarations and not the full definitions are necessary.
Obviously, it is possible to implement <string> without actually providing the full definitions of all the templates std::basic_string uses (std::allocator, std::basic_istream, and std::basic_ostream). Furthermore, not only is it possible, doing so is likely to have a positive effect on compile-time efficiency.
But while it may seem perfectly reasonable to expect a program that uses the std::basic_string insertion and extraction operators to also explicitly include <istream> or <ostream>, respectively, it doesn't seem reasonable to also expect it to explicitly include <memory>. Since what's reasonable and what isn't is highly subjective one would expect the standard to specify what can and what cannot be assumed. Unfortunately, that isn't the case.
The examples below demonstrate the issue.
Example 1:
It is not clear whether the following program is complete:
#include <string>
extern std::basic_ostream<char> &strm;
int main () {
strm << std::string ("Hello, World!\n");
}
or whether one must explicitly include <memory> or <ostream> (or both) in addition to <string> in order for the program to compile.
Example 2:
Similarly, it is unclear whether the following program is complete:
#include <istream>
extern std::basic_iostream<char> &strm;
int main () {
strm << "Hello, World!\n";
}
or whether one needs to explicitly include <ostream>, and perhaps even other headers containing the definitions of other required templates:
#include <ios>
#include <istream>
#include <ostream>
#include <streambuf>
extern std::basic_iostream<char> &strm;
int main () {
strm << "Hello, World!\n";
}
Example 3:
Likewise, it seems unclear whether the program below is complete:
#include <iterator>
bool foo (std::istream_iterator<int> a, std::istream_iterator<int> b)
{
return a == b;
}
int main () { }
or whether one should be required to include <istream>.
There are many more examples that demonstrate this lack of a requirement. I believe that in a good number of cases it would be unreasonable to require that a program explicitly include all the headers necessary for a particular template to be specialized, but I think that there are cases such as some of those above where it would be desirable to allow implementations to include only as much as necessary and not more.
[ post Bellevue: ]
Position taken in prior reviews is that the idea of a table of header dependencies is a good one. Our view is that a full paper is needed to do justice to this, and we've made that recommendation to the issue author.
[ 2009-07 Frankfurt ]
NAD. Handled by LWG 1178.
Proposed resolution:
For every C++ library header, supply a minimum set of other C++ library headers that are required to be included by that header. The proposed list is below (C++ headers for C Library Facilities, table 12 in 17.4.1.2, p3, are omitted):
+------------+--------------------+ | C++ header |required to include | +============+====================+ |<algorithm> | | +------------+--------------------+ |<bitset> | | +------------+--------------------+ |<complex> | | +------------+--------------------+ |<deque> |<memory> | +------------+--------------------+ |<exception> | | +------------+--------------------+ |<fstream> |<ios> | +------------+--------------------+ |<functional>| | +------------+--------------------+ |<iomanip> |<ios> | +------------+--------------------+ |<ios> |<streambuf> | +------------+--------------------+ |<iosfwd> | | +------------+--------------------+ |<iostream> |<istream>, <ostream>| +------------+--------------------+ |<istream> |<ios> | +------------+--------------------+ |<iterator> | | +------------+--------------------+ |<limits> | | +------------+--------------------+ |<list> |<memory> | +------------+--------------------+ |<locale> | | +------------+--------------------+ |<map> |<memory> | +------------+--------------------+ |<memory> | | +------------+--------------------+ |<new> |<exception> | +------------+--------------------+ |<numeric> | | +------------+--------------------+ |<ostream> |<ios> | +------------+--------------------+ |<queue> |<deque> | +------------+--------------------+ |<set> |<memory> | +------------+--------------------+ |<sstream> |<ios>, <string> | +------------+--------------------+ |<stack> |<deque> | +------------+--------------------+ |<stdexcept> | | +------------+--------------------+ |<streambuf> |<ios> | +------------+--------------------+ |<string> |<memory> | +------------+--------------------+ |<strstream> | | +------------+--------------------+ |<typeinfo> |<exception> | +------------+--------------------+ |<utility> | | +------------+--------------------+ |<valarray> | | +------------+--------------------+ |<vector> |<memory> | +------------+--------------------+
Rationale:
The portability problem is real. A program that works correctly on one implementation might fail on another, because of different header dependencies. This problem was understood before the standard was completed, and it was a conscious design choice.
One possible way to deal with this, as a library extension, would be an <all> header.
Hinnant: It's time we dealt with this issue for C++0X. Reopened.
Section: 22.4.2 [category.numeric] Status: NAD Submitter: Howard Hinnant Opened: 2001-10-13 Last modified: 2007-01-15
View all issues with NAD status.
Discussion:
When both grouping and showbase are active and the basefield is octal, does the leading 0 participate in the grouping or not? For example, should one format as: 0,123,456 or 0123,456?
An analogy can be drawn with hexadecimal. It appears that 0x123,456 is preferred over 0x,123,456. However, this analogy is not universally accepted to apply to the octal base. The standard is not clear on how to format (or parse) in this manner.
Proposed resolution:
Insert into 22.4.3.1.2 [facet.numpunct.virtuals] paragraph 3, just before the last sentence:
The leading hexadecimal base specifier "0x" does not participate in grouping. The leading '0' octal base specifier may participate in grouping. It is unspecified if the leading '0' participates in formatting octal numbers. In parsing octal numbers, the implementation is encouraged to accept both the leading '0' participating in the grouping, and not participating (e.g. 0123,456 or 0,123,456).
Rationale:
The current behavior may be unspecified, but it's not clear that it matters. This is an obscure corner case, since grouping is usually intended for the benefit of humans and oct/hex prefixes are usually intended for the benefit of machines. There is not a strong enough consensus in the LWG for action.
Section: 20.3.3 [pairs] Status: Dup Submitter: Andy Sawyer Opened: 2001-10-23 Last modified: 2008-01-05
View other active issues in [pairs].
View all other issues in [pairs].
View all issues with Dup status.
Duplicate of: 532
Discussion:
The current wording of 20.2.2 [lib.pairs] p6 precludes the use of operator< on any pair type which contains a pointer.
Proposed resolution:
In 20.3.3 [pairs] paragraph 6, replace:
Returns: x.first < y.first || (!(y.first < x.first) && x.second <
y.second).
With:
Returns: std::less<T1>()( x.first, y.first ) ||
(!std::less<T1>()( y.first, x.first) &&
std::less<T2>()( x.second, y.second ) )
Rationale:
This is an instance of a much more general problem. If we want operator< to translate to std::less for pairs of pointers, where do we draw the line? The same issue applies to individual pointers, smart pointer wrappers, std::vector<T*>, and so on.
Andy Koenig suggests that the real issue here is that we aren't distinguishing adequately between two different orderings, a "useful ordering" and a "canonical ordering" that's used just because we sometimes need some ordering without caring much which ordering it is. Another example of the later is typeinfo's before.
Section: 20.8.5.1 [allocator.members], 20.2.2 [allocator.requirements], 17.6.1.1 [contents] Status: Dup Submitter: Nathan Myers Opened: 2001-10-25 Last modified: 2007-10-11
View all other issues in [allocator.members].
View all issues with Dup status.
Duplicate of: 634
Discussion:
See c++std-lib-9006 and c++std-lib-9007. This issue is taken verbatim from -9007.
The core language feature allowing definition of operator&() applied to any non-builtin type makes that operator often unsafe to use in implementing libraries, including the Standard Library. The result is that many library facilities fail for legal user code, such as the fragment
class A { private: A* operator&(); };
std::vector<A> aa;
class B { };
B* operator&(B&) { return 0; }
std::vector<B> ba;
In particular, the requirements table for Allocator (Table 32) specifies no semantics at all for member address(), and allocator<>::address is defined in terms of unadorned operator &.
Proposed resolution:
In 20.6.1.1, Change the definition of allocator<>::address from:
Returns: &x
to:
Returns: The value that the built in operator&(x) would return if not overloaded.
In 20.1.6, Table 32, add to the Notes column of the a.address(r) and a.address(s) lines, respectively:
allocator<T>::address(r) allocator<T>::address(s)
In addition, in clause 17.4.1.1, add a statement:
The Standard Library does not apply operator& to any type for which operator& may be overloaded.
Rationale:
The LWG believes both examples are ill-formed. The contained type is required to be CopyConstructible (20.2.1 [utility.arg.requirements]), and that includes the requirement that &t return the usual types and values. Since allocators are intended to be used in conjunction with containers, and since the CopyConstructible requirements appear to have been written to deal with the concerns of this issue, the LWG feels it is NAD unless someone can come up with a well-formed example exhibiting a problem.
It may well be that the CopyConstructible requirements are too restrictive and that either the container requirements or the CopyConstructive requirements should be relaxed, but that's a far larger issue. Marking this issue as "future" as a pointer to that larger issue.
Section: 20.7 [function.objects] Status: NAD Editorial Submitter: Dale Riley Opened: 2001-11-12 Last modified: 2007-04-24
View all other issues in [function.objects].
View all issues with NAD Editorial status.
Discussion:
In 20.7 [function.objects] the header <functional> synopsis declares the unary_negate and binary_negate function objects as struct. However in 20.7.10 [negators] the unary_negate and binary_negate function objects are defined as class. Given the context, they are not "basic function objects" like negate, so this is either a typo or an editorial oversight.
[Taken from comp.std.c++]
Proposed resolution:
Change the synopsis to reflect the useage in 20.7.10 [negators]
[Curaçao: Since the language permits "struct", the LWG views this as NAD. They suggest, however, that the Project Editor might wish to make the change as editorial.]
Section: 20.3.3 [pairs] Status: NAD Editorial Submitter: Martin Sebor Opened: 2001-12-02 Last modified: 2008-01-05
View other active issues in [pairs].
View all other issues in [pairs].
View all issues with NAD Editorial status.
Discussion:
The class template std::pair defines a template ctor (20.2.2, p4) but no template assignment operator. This may lead to inefficient code since assigning an object of pair<C, D> to pair<A, B> where the types C and D are distinct from but convertible to A and B, respectively, results in a call to the template copy ctor to construct an unnamed temporary of type pair<A, B> followed by an ordinary (perhaps implicitly defined) assignment operator, instead of just a straight assignment.
Proposed resolution:
Add the following declaration to the definition of std::pair:
template<class U, class V>
pair& operator=(const pair<U, V> &p);
And also add a paragraph describing the effects of the function template to the end of 20.2.2:
template<class U, class V>
pair& operator=(const pair<U, V> &p);
Effects: first = p.first; second = p.second; Returns: *this
[Curaçao: There is no indication this is was anything other than a design decision, and thus NAD. May be appropriate for a future standard.]
[ Pre Bellevue: It was recognized that this was taken care of by N1856, and thus moved from NAD Future to NAD Editorial. ]
Section: 22.4.1 [category.ctype] Status: NAD Submitter: Matt Austern Opened: 2002-01-23 Last modified: 2006-12-27
View all other issues in [category.ctype].
View all issues with NAD status.
Discussion:
What should the following program print?
#include <locale>
#include <iostream>
class my_ctype : public std::ctype<char>
{
typedef std::ctype<char> base;
public:
my_ctype(std::size_t refs = 0) : base(my_table, false, refs)
{
std::copy(base::classic_table(), base::classic_table() + base::table_size,
my_table);
my_table[(unsigned char) '_'] = (base::mask) (base::print | base::space);
}
private:
mask my_table[base::table_size];
};
int main()
{
my_ctype ct;
std::cout << "isspace: " << ct.is(std::ctype_base::space, '_') << " "
<< "isalpha: " << ct.is(std::ctype_base::alpha, '_') << std::endl;
}
The goal is to create a facet where '_' is treated as whitespace.
On gcc 3.0, this program prints "isspace: 1 isalpha: 0". On Microsoft C++ it prints "isspace: 1 isalpha: 1".
I believe that both implementations are legal, and the standard does not give enough guidance for users to be able to use std::ctype's protected interface portably.
The above program assumes that ctype_base::mask enumerators like space and print are disjoint, and that the way to say that a character is both a space and a printing character is to or those two enumerators together. This is suggested by the "exposition only" values in 22.4.1 [category.ctype], but it is nowhere specified in normative text. An alternative interpretation is that the more specific categories subsume the less specific. The above program gives the results it does on the Microsoft compiler because, on that compiler, print has all the bits set for each specific printing character class.
From the point of view of std::ctype's public interface, there's no important difference between these two techniques. From the point of view of the protected interface, there is. If I'm defining a facet that inherits from std::ctype<char>, I'm the one who defines the value that table()['a'] returns. I need to know what combination of mask values I should use. This isn't so very esoteric: it's exactly why std::ctype has a protected interface. If we care about users being able to write their own ctype facets, we have to give them a portable way to do it.
Related reflector messages: lib-9224, lib-9226, lib-9229, lib-9270, lib-9272, lib-9273, lib-9274, lib-9277, lib-9279.
Issue 339 is related, but not identical. The proposed resolution if issue 339 says that ctype_base::mask must be a bitmask type. It does not say that the ctype_base::mask elements are bitmask elements, so it doesn't directly affect this issue.
More comments from Benjamin Kosnik, who believes that that C99 compatibility essentially requires what we're calling option 1 below.
I think the C99 standard is clear, that isspace -> !isalpha.
--------
#include <locale>
#include <iostream>
class my_ctype : public std::ctype<char>
{
private:
typedef std::ctype<char> base;
mask my_table[base::table_size];
public:
my_ctype(std::size_t refs = 0) : base(my_table, false, refs)
{
std::copy(base::classic_table(), base::classic_table() + base::table_size,
my_table);
mask both = base::print | base::space;
my_table[static_cast<mask>('_')] = both;
}
};
int main()
{
using namespace std;
my_ctype ct;
cout << "isspace: " << ct.is(ctype_base::space, '_') << endl;
cout << "isprint: " << ct.is(ctype_base::print, '_') << endl;
// ISO C99, isalpha iff upper | lower set, and !space.
// 7.5, p 193
// -> looks like g++ behavior is correct.
// 356 -> bitmask elements are required for ctype_base
// 339 -> bitmask type required for mask
cout << "isalpha: " << ct.is(ctype_base::alpha, '_') << endl;
}
Proposed resolution:
Informally, we have three choices:
Either of the first two options is just as good from the standpoint of portability. Either one will require some implementations to change.
Rationale:
The LWG agrees that this is a real ambiguity, and that both interpretations are conforming under the existing standard. However, there's no evidence that it's causing problems for real users. Users who want to define ctype facets portably can test the ctype_base masks to see which interpretation is being used.
Section: 26.8 [c.math] Status: NAD Editorial Submitter: Ray Lischner Opened: 2002-02-26 Last modified: 2007-04-24
View all other issues in [c.math].
View all issues with NAD Editorial status.
Discussion:
The float versions of the math functions have no meaningful value to return for a range error. The long double versions have a value they can return, but it isn't necessarily the most reasonable value.
Section 26.5 [lib.c.math], paragraph 5, says that C++ "adds float and long double overloaded versions of these functions, with the same semantics," referring to the math functions from the C90 standard.
The C90 standard, in section 7.5.1, paragraph 3, says that functions return "the value of the macro HUGE_VAL" when they encounter a range error. Section 7.5, paragraph 2, defines HUGE_VAL as a macro that "expands to a positive double expression, not necessarily representable as a float."
Therefore, the float versions of the math functions have no way to signal a range error. [Curaçao: The LWG notes that this isn't strictly correct, since errno is set.] The semantics require that they return HUGE_VAL, but they cannot because HUGE_VAL might not be representable as a float.
The problem with long double functions is less severe because HUGE_VAL is representable as a long double. On the other hand, it might not be a "huge" long double value, and might fall well within the range of normal return values for a long double function. Therefore, it does not make sense for a long double function to return a double (HUGE_VAL) for a range error.
Proposed resolution:
Curaçao: C99 was faced with a similar problem, which they fixed by adding HUGE_VALF and HUGE_VALL in addition to HUGE_VAL.
C++ must also fix, but it should be done in the context of the general C99 based changes to C++, not via DR. Thus the LWG in Curaçao felt the resolution should be NAD, FUTURE, but the issue is being held open for one more meeting to ensure LWG members not present during the discussion concur.
Rationale:
Will be fixed as part of more general work in the TR.
Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: NAD Submitter: Martin Sebor Opened: 2002-03-12 Last modified: 2007-01-15
View other active issues in [facet.num.put.virtuals].
View all other issues in [facet.num.put.virtuals].
View all issues with NAD status.
Discussion:
22.2.2.2.2, p12 specifies that thousands_sep is to be inserted only for integral types (issue 282 suggests that this should be done for all arithmetic types).
22.2.2.1.2, p12 requires that grouping be checked for all extractors including that for void*.
I don't think that's right. void* values should not be checked for grouping, should they? (Although if they should, then num_put needs to write them out, otherwise their extraction will fail.)
Proposed resolution:
Change the first sentence of 22.2.2.2.2, p12 from
Digit grouping is checked. That is, the positions of discarded separators is examined for consistency with use_facet<numpunct<charT> >(loc).grouping(). If they are not consistent then ios_base::failbit is assigned to err.
to
Except for conversions to void*, digit grouping is checked...
Rationale:
This would be a change: as it stands, the standard clearly specifies that grouping applies to void*. A survey of existing practice shows that most existing implementations do that, as they should.
Section: 27 [input.output] Status: NAD Submitter: Walter Brown, Marc Paterno Opened: 2002-05-10 Last modified: 2006-12-27
View all other issues in [input.output].
View all issues with NAD status.
Discussion:
The following member functions are declared const, yet return non-const pointers. We believe they are should be changed, because they allow code that may surprise the user. See document N1360 for details and rationale.
[Santa Cruz: the real issue is that we've got const member functions that return pointers to non-const, and N1360 proposes replacing them by overloaded pairs. There isn't a consensus about whether this is a real issue, since we've never said what our constness policy is for iostreams. N1360 relies on a distinction between physical constness and logical constness; that distinction, or those terms, does not appear in the standard.]
Proposed resolution:
In 27.4.4 and 27.4.4.2
Replace
basic_ostream<charT,traits>* tie() const;
with
basic_ostream<charT,traits>* tie(); const basic_ostream<charT,traits>* tie() const;
and replace
basic_streambuf<charT,traits>* rdbuf() const;
with
basic_streambuf<charT,traits>* rdbuf(); const basic_streambuf<charT,traits>* rdbuf() const;
In 27.5.2 and 27.5.2.3.1
Replace
char_type* eback() const;
with
char_type* eback(); const char_type* eback() const;
Replace
char_type gptr() const;
with
char_type* gptr(); const char_type* gptr() const;
Replace
char_type* egptr() const;
with
char_type* egptr(); const char_type* egptr() const;
In 27.5.2 and 27.5.2.3.2
Replace
char_type* pbase() const;
with
char_type* pbase(); const char_type* pbase() const;
Replace
char_type* pptr() const;
with
char_type* pptr(); const char_type* pptr() const;
Replace
char_type* epptr() const;
with
char_type* epptr(); const char_type* epptr() const;
In 27.7.2, 27.7.2.2, 27.7.3 27.7.3.2, 27.7.4, and 27.7.6
Replace
basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
with
basic_stringbuf<charT,traits,Allocator>* rdbuf(); const basic_stringbuf<charT,traits,Allocator>* rdbuf() const;
In 27.8.1.5, 27.8.1.7, 27.8.1.8, 27.8.1.10, 27.8.1.11, and 27.8.1.13
Replace
basic_filebuf<charT,traits>* rdbuf() const;
with
basic_filebuf<charT,traits>* rdbuf(); const basic_filebuf<charT,traits>* rdbuf() const;
Rationale:
The existing specification is a bit sloppy, but there's no particular reason to change this other than tidiness, and there are a number of ways in which streams might have been designed differently if we were starting today. There's no evidence that the existing constness policy is harming users. We might consider a different constness policy as part of a full stream redesign.
Section: 25.3.8 [alg.remove] Status: NAD Submitter: Anthony Williams Opened: 2002-05-13 Last modified: 2006-12-27
View all other issues in [alg.remove].
View all issues with NAD status.
Discussion:
remove_copy and remove_copy_if (25.3.8 [alg.remove]) permit their input range to be marked with Input Iterators. However, since two operations are required against the elements to copy (comparison and assigment), when the input range uses Input Iterators, a temporary copy must be taken to avoid dereferencing the iterator twice. This therefore requires the value type of the InputIterator to be CopyConstructible. If the iterators are at least Forward Iterators, then the iterator can be dereferenced twice, or a reference to the result maintained, so the temporary is not required.
Proposed resolution:
Add "If InputIterator does not meet the requirements of forward iterator, then the value type of InputIterator must be copy constructible. Otherwise copy constructible is not required." to 25.3.8 [alg.remove] paragraph 6.
Rationale:
The assumption is that an input iterator can't be dereferenced twice. There's no basis for that assumption in the Standard.
Section: 21.4.6.6 [string::replace] Status: NAD Editorial Submitter: Beman Dawes Opened: 2002-06-03 Last modified: 2007-04-24
View all issues with NAD Editorial status.
Discussion:
21.4.6.6 [string::replace] basic_string::replace, second signature, given in paragraph 1, has two "Throws" paragraphs (3 and 5).
In addition, the second "Throws" paragraph (5) includes specification (beginning with "Otherwise, the function replaces ...") that should be part of the "Effects" paragraph.
Proposed resolution:
Rationale:
This is editorial. Both "throws" statements are true. The bug is just that the second one should be a sentence, part of the "Effects" clause, not a separate "Throws". The project editor has been notified.
Section: 17.6.4.10 [res.on.exception.handling], 18.7.1 [type.info] Status: NAD Submitter: Randy Maddox Opened: 2002-07-22 Last modified: 2006-12-27
View all other issues in [res.on.exception.handling].
View all issues with NAD status.
Discussion:
Paragraph 3 under clause 17.6.4.10 [res.on.exception.handling], Restrictions on Exception Handling, states that "Any other functions defined in the C++ Standard Library that do not have an exception-specification may throw implementation-defined exceptions unless otherwise specified." This statement is followed by a reference to footnote 178 at the bottom of that page which states, apparently in reference to the C++ Standard Library, that "Library implementations are encouraged (but not required) to report errors by throwing exceptions from (or derived from) the standard exceptions."
These statements appear to be in direct contradiction to clause 18.7.1 [type.info], which states "The class exception defines the base class for the types of objects thrown as exceptions by the C++ Standard library components ...".
Is this inconsistent?
Proposed resolution:
Rationale:
Clause 17 is setting the overall library requirements, and it's clear and consistent. This sentence from Clause 18 is descriptive, not setting a requirement on any other class.
Section: 22.4.6.3.1 [locale.moneypunct.members], 22.4.6.3.2 [locale.moneypunct.virtuals] Status: NAD Submitter: Ray Lischner Opened: 2002-08-08 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
In section 22.4.6.3.1 [locale.moneypunct.members], frac_digits() returns type "int". This implies that frac_digits() might return a negative value, but a negative value is nonsensical. It should return "unsigned".
Similarly, in section 22.4.6.3.2 [locale.moneypunct.virtuals], do_frac_digits() should return "unsigned".
Proposed resolution:
Rationale:
Regardless of whether the return value is int or unsigned, it's always conceivable that frac_digits might return a nonsensical value. (Is 4294967295 really any better than -1?) The clients of moneypunct, the get and put facets, can and do perform range checks.
Section: 21.4.6.4 [string::insert] Status: NAD Submitter: Ray Lischner Opened: 2002-08-16 Last modified: 2006-12-27
View all other issues in [string::insert].
View all issues with NAD status.
Discussion:
Section 21.4.6.4 [string::insert], paragraph 4, contains the following, "Then throws length_error if size() >= npos - rlen."
Related to DR 83, this sentence should probably be removed.
Proposed resolution:
Rationale:
This requirement is redundant but correct. No change is needed.
Section: 22.3.1 [locale] Status: Dup Submitter: Martin Sebor Opened: 2002-09-06 Last modified: 2006-12-30
View all other issues in [locale].
View all issues with Dup status.
Duplicate of: 31
Discussion:
I think there is a problem with 22.1.1, p6 which says that
-6- An instance of locale is immutable; once a facet reference
is obtained from it, that reference remains usable as long
as the locale value itself exists.
and 22.1.1.2, p4:
const locale& operator=(const locale& other) throw();
-4- Effects: Creates a copy of other, replacing the current value.
How can a reference to a facet obtained from a locale object remain valid after an assignment that clearly must replace all the facets in the locale object? Imagine a program such as this
std::locale loc ("de_DE");
const std::ctype<char> &r0 = std::use_facet<std::ctype<char> >(loc);
loc = std::locale ("en_US");
const std::ctype<char> &r1 = std::use_facet<std::ctype<char> >(loc);
Is r0 really supposed to be preserved and destroyed only when loc goes out of scope?
Proposed resolution:
[Summer '04 mid-meeting mailing: Martin and Dietmar believe this is a duplicate of issue 31 and recommend that it be closed. ]
Section: 22.4.1.4 [locale.codecvt] Status: NAD Submitter: Martin Sebor Opened: 2002-08-30 Last modified: 2009-07-14
View all other issues in [locale.codecvt].
View all issues with NAD status.
Discussion:
It seems that the descriptions of codecvt do_in() and do_out() leave sufficient room for interpretation so that two implementations of codecvt may not work correctly with the same filebuf. Specifically, the following seems less than adequately specified:
Finally, the conditions described at the end of 22.4.1.4.2 [locale.codecvt.virtuals], p4 don't seem to be possible:
"A return value of partial, if (from_next == from_end), indicates that either the destination sequence has not absorbed all the available destination elements, or that additional source elements are needed before another destination element can be produced."
If the value is partial, it's not clear to me that (from_next ==from_end) could ever hold if there isn't enough room in the destination buffer. In order for (from_next==from_end) to hold, all characters in that range must have been successfully converted (according to 22.4.1.4.2 [locale.codecvt.virtuals], p2) and since there are no further source characters to convert, no more room in the destination buffer can be needed.
It's also not clear to me that (from_next==from_end) could ever hold if additional source elements are needed to produce another destination character (not element as incorrectly stated in the text). partial is returned if "not all source characters have been converted" according to Table 53, which also implies that (from_next==from) does NOT hold.
Could it be that the intended qualifying condition was actually (from_next != from_end), i.e., that the sentence was supposed to read
"A return value of partial, if (from_next != from_end),..."
which would make perfect sense, since, as far as I understand it, partial can only occur if (from_next != from_end)?
[Lillehammer: Defer for the moment, but this really needs to be fixed. Right now, the description of codecvt is too vague for it to be a useful contract between providers and clients of codecvt facets. (Note that both vendors and users can be both providers and clients of codecvt facets.) The major philosophical issue is whether the standard should only describe mappings that take a single wide character to multiple narrow characters (and vice versa), or whether it should describe fully general N-to-M conversions. When the original standard was written only the former was contemplated, but today, in light of the popularity of utf8 and utf16, that doesn't seem sufficient for C++0x. Bill supports general N-to-M conversions; we need to make sure Martin and Howard agree.]
[ 2009-07 Frankfurt ]
codecvt is meant to be a 1-to-N to N-to-1 conversion. It does not work well for N-to-M conversions. wbuffer_convert now exists, and handles N-to-M cases. Also, there is a new specialization of codecvt that permits UTF-16 <-> UTF-8 conversions.
NAD without prejudice. Will reopen if proposed resolution is supplied.
Proposed resolution:
Section: 17 [library] Status: NAD Submitter: Matt Austern Opened: 2002-10-23 Last modified: 2007-04-18
View other active issues in [library].
View all other issues in [library].
View all issues with NAD status.
Discussion:
Many function templates have parameters that are passed by value; a typical example is find_if's pred parameter in 25.2.5 [alg.find]. Are the corresponding template parameters (Predicate in this case) implicitly required to be CopyConstructible, or does that need to be spelled out explicitly?
This isn't quite as silly a question as it might seem to be at first sight. If you call find_if in such a way that template argument deduction applies, then of course you'll get call by value and you need to provide a copy constructor. If you explicitly provide the template arguments, however, you can force call by reference by writing something like find_if<my_iterator, my_predicate&>. The question is whether implementation are required to accept this, or whether this is ill-formed because my_predicate& is not CopyConstructible.
The scope of this problem, if it is a problem, is unknown. Function object arguments to generic algorithms in clauses 25 [algorithms] and 26 [numerics] are obvious examples. A review of the whole library is necessary.
[ This is really two issues. First, predicates are typically passed by value but we don't say they must be Copy Constructible. They should be. Second: is specialization allowed to transform value arguments into references? References aren't copy constructible, so this should not be allowed. ]
[ 2007-01-12, Howard: First, despite the note above, references are copy constructible. They just aren't assignable. Second, this is very closely related to 92 and should be consistent with that. That issue already says that implementations are allowed to copy function objects. If one passes in a reference, it is copyable, but susceptible to slicing if one passes in a reference to a base. Third, with rvalue reference in the language one only needs to satisfy MoveConstructible to pass an rvalue "by value". Though the function might still copy the function object internally (requiring CopyConstructible). Finally (and fwiw), if we wanted to, it is easy to code all of the std::algorithms such that they do not copy function objects internally. One merely passes them by reference internally if desired (this has been fully implemented and shipped for several years). If this were mandated, it would reverse 92, allowing function objects to reliably maintain state. E.g. the example in 92 would reliably remove only the third element. ]
Proposed resolution:
Recommend NAD.
Rationale:
Generic algorithms will be marked with concepts and these will imply a requirement of MoveConstructible (not CopyConstructible). The signature of the function will then precisely describe and enforce the precise requirements.
Section: 26.4 [complex.numbers] Status: NAD Submitter: Gabriel Dos Reis Opened: 2002-11-08 Last modified: 2008-02-27
View other active issues in [complex.numbers].
View all other issues in [complex.numbers].
View all issues with NAD status.
Discussion:
Practice with std::complex<> and the associative containers occasionally reveals artificial and distracting issues with constructs resembling: std::set<std::complex<double> > s;
The main reason for the above to fail is the absence of an approriate definition for std::less<std::complex<T> >. That in turn comes from the definition of the primary template std::less<> in terms of operator<.
The usual argument goes as follows: Since there is no ordering over the complex field compatible with field operations it makes little sense to define a function operator< operating on the datatype std::complex<T>. That is fine. However, that reasoning does not carry over to std::less<T> which is used, among other things, by associative containers as an ordering useful to meet complexity requirements.
Related issue: 348.
[ Pre Bellevue: Reopened at the request of Alisdair. ]
[ Bellevue: ]
This is a request for a design change, and not a defect in the standard. It is in scope to consider, but the group feels that it is not a change that we need to do. Is there a total ordering for floating point values, including NaN? There is not a clear enough solution or big enough problem for us to solve. Solving this problem would require solving the problem for floating point, which is equally unclear. The LWG noted that users who want to put objects into an associative container for which operator< isn't defined can simply provide their own comparison function object. NAD
Proposed resolution:
Informally: Add a specialization of std::less for std::complex.
Rationale:
Discussed in Santa Cruz. An overwhelming majority of the LWG believes this should not be treated a DR: it's a request for a design change, not a defect in the existing standard. Most people (10-3) believed that we probably don't want this change, period: as with issue 348, it's hard to know where to draw the line. The LWG noted that users who want to put objects into an associative container for which operator< isn't defined can simply provide their own comparison function object.
Section: 20.2.1 [utility.arg.requirements] Status: NAD Editorial Submitter: Doug Gregor Opened: 2002-10-24 Last modified: 2008-03-14
View other active issues in [utility.arg.requirements].
View all other issues in [utility.arg.requirements].
View all issues with NAD Editorial status.
Discussion:
The CopyConstructible requirements in Table 30 state that for an object t of type T (where T is CopyConstructible), the expression &t returns the address of t (with type T*). This requirement is overly strict, in that it disallows types that overload operator& to not return a value of type T*. This occurs, for instance, in the Boost.Lambda library, where operator& is overloaded for a Boost.Lambda function object to return another function object.
Example:
std::vector<int> u, v; int x; // ... std::transform(u.begin(), u.end(), std::back_inserter(v), _1 * x);
_1 * x returns an unnamed function object with operator& overloaded to not return T* , therefore rendering the std::transform call ill-formed. However, most standard library implementations will compile this code properly, and the viability of such binder libraries is severely hindered by the unnecessary restriction in the CopyConstructible requirements.
For reference, the address of an object can be retrieved without using the address-of operator with the following function template:
template <typename T> T* addressof(T& v)
{
return reinterpret_cast<T*>(
&const_cast<char&>(reinterpret_cast<const volatile char &>(v)));
}
Note: this relates directly to library issue 350, which will need to be reexamined if the CopyConstructible requirements change.
Proposed resolution:
Remove the last two rows of Table 30, eliminating the requirements that &t and &u return the address of t and u, respectively.
Rationale:
This was a deliberate design decision. Perhaps it should be reconsidered for C++0x.
Section: 24.2.1 [input.iterators] Status: NAD Submitter: Corwin Joy Opened: 2002-12-11 Last modified: 2006-12-27
View all other issues in [input.iterators].
View all issues with NAD status.
Discussion:
In section 24.2.1 [input.iterators] table 72 - 'Input Iterator Requirements' we have as a postcondition of *a: "If a==b and (a, b) is in the domain of == then *a is equivalent to *b".
In section 24.6.3.5 [istreambuf.iterator::equal] it states that "istreambuf_iterator::equal returns true if and only if both iterators are at end-of-stream, or neither is at end-of-stream, regardless of what streambuf object they use." (My emphasis).
The defect is that either 'equivalent' needs to be more precisely defined or the conditions for equality in 24.6.3.5 [istreambuf.iterator::equal] are incorrect. (Or both).
Consider the following example:
#include <iostream>
#include <fstream>
#include <iterator>
using namespace std;
int main() {
ifstream file1("file1.txt"), file2("file2.txt");
istreambuf_iterator<char> f1(file1), f2(file2);
cout << "f1 == f2 : " << boolalpha << (f1 == f2) << endl;
cout << "f1 = " << *f1 << endl;
cout << "f2 = " << *f2 << endl;
return 0;
}
Now assuming that neither f1 or f2 are at the end-of-stream then f1 == f2 by 24.6.3.5 [istreambuf.iterator::equal].
However, it is unlikely that *f1 will give the same value as *f2 except by accident.
So what does *f1 'equivalent' to *f2 mean? I think the standard should be clearer on this point, or at least be explicit that this does not mean that *f1 and *f2 are required to have the same value in the case of input iterators.
Proposed resolution:
Rationale:
The two iterators aer not in the domain of ==
Section: 22.4.1.4.2 [locale.codecvt.virtuals] Status: NAD Editorial Submitter: Alberto Barbati Opened: 2002-12-24 Last modified: 2008-07-02
View all other issues in [locale.codecvt.virtuals].
View all issues with NAD Editorial status.
Discussion:
this DR follows the discussion on the previous thread "codecvt::do_in not consuming external characters". It's just a clarification issue and not a request for a change.
Can do_in()/do_out() produce output characters without consuming input characters as a result of operation on state?
Proposed resolution:
Add a note at the end of 22.4.1.4.2 [locale.codecvt.virtuals], paragraph 3:
[Note: As a result of operations on state, it can return ok or partial and set from_next == from and to_next != to. --end note]
Rationale:
The submitter believes that standard already provides an affirmative answer to the question. However, the current wording has induced a few library implementors to make the incorrect assumption that do_in()/do_out() always consume at least one internal character when they succeed.
The submitter also believes that the proposed resolution is not in conflict with the related issue 76. Moreover, by explicitly allowing operations on state to produce characters, a codecvt implementation may effectively implement N-to-M translations without violating the "one character at a time" principle described in such issue. On a side note, the footnote in the proposed resolution of issue 76 that informally rules out N-to-M translations for basic_filebuf should be removed if this issue is accepted as valid.
[ Kona (2007): The proposed resolution is to add a note. Since this is non-normative, the issue is editorial, but we believe that the note is correct. Proposed Disposition: NAD, Editorial ]
Section: 27.7.2.6.1 [ostream.formatted.reqmts] Status: NAD Submitter: Martin Sebor Opened: 2002-12-27 Last modified: 2009-07-14
View all issues with NAD status.
Discussion:
There is a contradiction in Formatted output about what bit is supposed to be set if the formatting fails. On sentence says it's badbit and another that it's failbit.
27.6.2.5.1, p1 says in the Common Requirements on Formatted output functions:
... If the generation fails, then the formatted output function
does setstate(ios::failbit), which might throw an exception.
27.6.2.5.2, p1 goes on to say this about Arithmetic Inserters:
... The formatting conversion occurs as if it performed the following code fragment:
bool failed =
use_facet<num_put<charT,ostreambuf_iterator<charT,traits>
> >
(getloc()).put(*this, *this, fill(), val). failed();
... If failed is true then does setstate(badbit) ...
The original intent of the text, according to Jerry Schwarz (see c++std-lib-10500), is captured in the following paragraph:
In general "badbit" should mean that the stream is unusable because of some underlying failure, such as disk full or socket closure; "failbit" should mean that the requested formatting wasn't possible because of some inconsistency such as negative widths. So typically if you clear badbit and try to output something else you'll fail again, but if you clear failbit and try to output something else you'll succeed.
In the case of the arithmetic inserters, since num_put cannot report failure by any means other than exceptions (in response to which the stream must set badbit, which prevents the kind of recoverable error reporting mentioned above), the only other detectable failure is if the iterator returned from num_put returns true from failed().
Since that can only happen (at least with the required iostream specializations) under such conditions as the underlying failure referred to above (e.g., disk full), setting badbit would seem to be the appropriate response (indeed, it is required in 27.6.2.5.2, p1). It follows that failbit can never be directly set by the arithmetic (it can only be set by the sentry object under some unspecified conditions).
The situation is different for other formatted output functions which can fail as a result of the streambuf functions failing (they may do so by means other than exceptions), and which are then required to set failbit.
The contradiction, then, is that ostream::operator<<(int) will set badbit if the disk is full, while operator<<(ostream&, char) will set failbit under the same conditions. To make the behavior consistent, the Common requirements sections for the Formatted output functions should be changed as proposed below.
[Kona: There's agreement that this is a real issue. What we decided at Kona: 1. An error from the buffer (which can be detected either directly from streambuf's member functions or by examining a streambuf_iterator) should always result in badbit getting set. 2. There should never be a circumstance where failbit gets set. That represents a formatting error, and there are no circumstances under which the output facets are specified as signaling a formatting error. (Even more so for string output that for numeric because there's nothing to format.) If we ever decide to make it possible for formatting errors to exist then the facets can signal the error directly, and that should go in clause 22, not clause 27. 3. The phrase "if generation fails" is unclear and should be eliminated. It's not clear whether it's intended to mean a buffer error (e.g. a full disk), a formatting error, or something else. Most people thought it was supposed to refer to buffer errors; if so, we should say so. Martin will provide wording.]
[ 2009-07 Frankfurt ]
NAD. This issue is already fixed.
Proposed resolution:
Rationale:
Section: 27.7.2.4 [ostream::sentry] Status: NAD Submitter: Martin Sebor Opened: 2003-01-05 Last modified: 2009-07-14
View all other issues in [ostream::sentry].
View all issues with NAD status.
Discussion:
While reviewing unformatted input member functions of istream for their behavior when they encounter end-of-file during input I found that the requirements vary, sometimes unexpectedly, and in more than one case even contradict established practice (GNU libstdc++ 3.2, IBM VAC++ 6.0, STLPort 4.5, SunPro 5.3, HP aCC 5.38, Rogue Wave libstd 3.1, and Classic Iostreams).
The following unformatted input member functions set eofbit if they encounter an end-of-file (this is the expected behavior, and also the behavior of all major implementations):
basic_istream<charT, traits>&
get (char_type*, streamsize, char_type);
Also sets failbit if it fails to extract any characters.
basic_istream<charT, traits>&
get (char_type*, streamsize);
Also sets failbit if it fails to extract any characters.
basic_istream<charT, traits>&
getline (char_type*, streamsize, char_type);
Also sets failbit if it fails to extract any characters.
basic_istream<charT, traits>&
getline (char_type*, streamsize);
Also sets failbit if it fails to extract any characters.
basic_istream<charT, traits>&
ignore (int, int_type);
basic_istream<charT, traits>&
read (char_type*, streamsize);
Also sets failbit if it encounters end-of-file.
streamsize readsome (char_type*, streamsize);
The following unformated input member functions set failbit but not eofbit if they encounter an end-of-file (I find this odd since the functions make it impossible to distinguish a general failure from a failure due to end-of-file; the requirement is also in conflict with all major implementation which set both eofbit and failbit):
int_type get();
basic_istream<charT, traits>&
get (char_type&);
These functions only set failbit of they extract no characters, otherwise they don't set any bits, even on failure (I find this inconsistency quite unexpected; the requirement is also in conflict with all major implementations which set eofbit whenever they encounter end-of-file):
basic_istream<charT, traits>&
get (basic_streambuf<charT, traits>&, char_type);
basic_istream<charT, traits>&
get (basic_streambuf<charT, traits>&);
This function sets no bits (all implementations except for STLport and Classic Iostreams set eofbit when they encounter end-of-file):
int_type peek ();
Informally, what we want is a global statement of intent saying that eofbit gets set if we trip across EOF, and then we can take away the specific wording for individual functions. A full review is necessary. The wording currently in the standard is a mishmash, and changing it on an individual basis wouldn't make things better. Dietmar will do this work.
[ 2009-07 Frankfurt ]
Moved to NAD. See 27.7.1.1 [istream] p3.
Proposed resolution:
Section: 27.7.1.3 [istream.unformatted] Status: NAD Submitter: Martin Sebor Opened: 2003-01-05 Last modified: 2006-12-27
View all other issues in [istream.unformatted].
View all issues with NAD status.
Discussion:
The Effects clauses for the two functions below violate the general requirements on unformatted input functions outlined in 27.6.1.3: they do not begin by constructing a sentry object. Instead, they begin by calling widen ('\n'), which may throw an exception. The exception is then allowed to propagate from the unformatted input function irrespective of the setting of exceptions().
Note that in light of 27.6.1.1, p3 and p4, the fact that the functions allow exceptions thrown from widen() to propagate may not strictly speaking be a defect (but the fact that the functions do not start by constructing a sentry object still is). However, since an exception thrown from ctype<charT> ::widen() during any other input operation (say, from within a call to num_get<charT>::get()) will be caught and cause badbit to be set, these two functions should not be treated differently for the sake of consistency.
Proposed resolution:
Rationale:
Not a defect. The standard is consistent, and the behavior required by the standard is unambiguous. Yes, it's theoretically possible for widen to throw. (Not that this will happen for the default ctype facet or for most real-world replacement ctype facets.) Users who define ctype facets that can throw, and who care about this behavior, can use alternative signatures that don't call widen.
Section: 22.4.1.1.2 [locale.ctype.virtuals] Status: NAD Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2009-07-14
View all other issues in [locale.ctype.virtuals].
View all issues with NAD status.
Discussion:
The Effects and Returns clauses of the do_widen() member function of the ctype facet fail to specify the behavior of the function on failure. That the function may not be able to simply cast the narrow character argument to the type of the result since doing so may yield the wrong value for some wchar_t encodings. Popular implementations of ctype<wchar_t> that use mbtowc() and UTF-8 as the native encoding (e.g., GNU glibc) will fail when the argument's MSB is set. There is no way for the the rest of locale and iostream to reliably detect this failure.
[Kona: This is a real problem. Widening can fail. It's unclear what the solution should be. Returning WEOF works for the wchar_t specialization, but not in general. One option might be to add a default, like narrow. But that's an incompatible change. Using traits::eof might seem like a good idea, but facets don't have access to traits (a recurring problem). We could have widen throw an exception, but that's a scary option; existing library components aren't written with the assumption that widen can throw.]
[ 2009-07 Frankfurt ]
NAD. The behavior is specified for all of the facets that an implementation is required to provide, for the basic character set.
Proposed resolution:
Section: 27.5.2.1.6 [ios::Init] Status: NAD Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2009-07-14
View all other issues in [ios::Init].
View all issues with NAD status.
Discussion:
The dtor of the ios_base::Init object is supposed to call flush() on the 6 standard iostream objects cout, cerr, clog, wcout, wcerr, and wclog. This call may cause an exception to be thrown.
17.4.4.8, p3 prohibits all library destructors from throwing exceptions.
The question is: What should this dtor do if one or more of these calls to flush() ends up throwing an exception? This can happen quite easily if one of the facets installed in the locale imbued in the iostream object throws.
[Kona: We probably can't do much better than what we've got, so the LWG is leaning toward NAD. At the point where the standard stream objects are being cleaned up, the usual error reporting mechanism are all unavailable. And exception from flush at this point will definitely cause problems. A quality implementation might reasonably swallow the exception, or call abort, or do something even more drastic.]
[ See 397 and 622 for related issues. ]
[ 2009-07 Frankfurt ]
Moved to NAD, no consensus for change.
Proposed resolution:
Section: 27.6.2.1 [streambuf.cons] Status: NAD Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2009-07-14
View all other issues in [streambuf.cons].
View all issues with NAD status.
Discussion:
The reflector thread starting with c++std-lib-11346 notes that the class template basic_streambuf, along with basic_stringbuf and basic_filebuf, is copy-constructible but that the semantics of the copy constructors are not defined anywhere. Further, different implementations behave differently in this respect: some prevent copy construction of objects of these types by declaring their copy ctors and assignment operators private, others exhibit undefined behavior, while others still give these operations well-defined semantics.
Note that this problem doesn't seem to be isolated to just the three types mentioned above. A number of other types in the library section of the standard provide a compiler-generated copy ctor and assignment operator yet fail to specify their semantics. It's believed that the only types for which this is actually a problem (i.e. types where the compiler-generated default may be inappropriate and may not have been intended) are locale facets. See issue 439.
[ 2009-07 Frankfurt ]
NAD. Option B is already in the Working Draft.
Proposed resolution:
27.5.2 [lib.streambuf]: Add into the synopsis, public section, just above the destructor declaration:
basic_streambuf(const basic_streambuf& sb); basic_streambuf& operator=(const basic_streambuf& sb);
Insert after 27.5.2.1, paragraph 2:
basic_streambuf(const basic_streambuf& sb);Constructs a copy of sb.
Postcondtions:
eback() == sb.eback() gptr() == sb.gptr() egptr() == sb.egptr() pbase() == sb.pbase() pptr() == sb.pptr() epptr() == sb.epptr() getloc() == sb.getloc()basic_streambuf& operator=(const basic_streambuf& sb);Assigns the data members of sb to this.
Postcondtions:
eback() == sb.eback() gptr() == sb.gptr() egptr() == sb.egptr() pbase() == sb.pbase() pptr() == sb.pptr() epptr() == sb.epptr() getloc() == sb.getloc()Returns: *this.
27.7.1 [lib.stringbuf]:
Option A:
Insert into the basic_stringbuf synopsis in the private section:
basic_stringbuf(const basic_stringbuf&); // not defined basic_stringbuf& operator=(const basic_stringbuf&); // not defined
Option B:
Insert into the basic_stringbuf synopsis in the public section:
basic_stringbuf(const basic_stringbuf& sb); basic_stringbuf& operator=(const basic_stringbuf& sb);27.7.1.1, insert after paragraph 4:
basic_stringbuf(const basic_stringbuf& sb);Constructs an independent copy of sb as if with sb.str(), and with the openmode that sb was constructed with.
Postcondtions:
str() == sb.str() gptr() - eback() == sb.gptr() - sb.eback() egptr() - eback() == sb.egptr() - sb.eback() pptr() - pbase() == sb.pptr() - sb.pbase() getloc() == sb.getloc()Note: The only requirement on epptr() is that it point beyond the initialized range if an output sequence exists. There is no requirement that epptr() - pbase() == sb.epptr() - sb.pbase().
basic_stringbuf& operator=(const basic_stringbuf& sb);After assignment the basic_stringbuf has the same state as if it were initially copy constructed from sb, except that the basic_stringbuf is allowed to retain any excess capacity it might have, which may in turn effect the value of epptr().
27.8.1.1 [lib.filebuf]
Insert at the bottom of the basic_filebuf synopsis:
private: basic_filebuf(const basic_filebuf&); // not defined basic_filebuf& operator=(const basic_filebuf&); // not defined
[Kona: this is an issue for basic_streambuf itself and for its derived classes. We are leaning toward allowing basic_streambuf to be copyable, and specifying its precise semantics. (Probably the obvious: copying the buffer pointers.) We are less sure whether the streambuf derived classes should be copyable. Howard will write up a proposal.]
[Sydney: Dietmar presented a new argument against basic_streambuf being copyable: it can lead to an encapsulation violation. Filebuf inherits from streambuf. Now suppose you inhert a my_hijacking_buf from streambuf. You can copy the streambuf portion of a filebuf to a my_hijacking_buf, giving you access to the pointers into the filebuf's internal buffer. Perhaps not a very strong argument, but it was strong enough to make people nervous. There was weak preference for having streambuf not be copyable. There was weak preference for having stringbuf not be copyable even if streambuf is. Move this issue to open for now. ]
[ 2007-01-12, Howard: Rvalue Reference Recommendations for Chapter 27 recommends protected copy constructor and assignment for basic_streambuf with the same semantics as would be generated by the compiler. These members aid in derived classes implementing move semantics. A protected copy constructor and copy assignment operator do not expose encapsulation more so than it is today as each data member of a basic_streambuf is already both readable and writable by derived classes via various get/set protected member functions (eback(), setp(), etc.). Rather a protected copy constructor and copy assignment operator simply make the job of derived classes implementing move semantics less tedious and error prone. ]
Rationale:
27.5.2 [lib.streambuf]: The proposed basic_streambuf copy constructor and assignment operator are the same as currently implied by the lack of declarations: public and simply copies the data members. This resolution is not a change but a clarification of the current standard.
27.7.1 [lib.stringbuf]: There are two reasonable options: A) Make basic_stringbuf not copyable. This is likely the status-quo of current implementations. B) Reasonable copy semantics of basic_stringbuf can be defined and implemented. A copyable basic_streambuf is arguably more useful than a non-copyable one. This should be considered as new functionality and not the fixing of a defect. If option B is chosen, ramifications from issue 432 are taken into account.
27.8.1.1 [lib.filebuf]: There are no reasonable copy semantics for basic_filebuf.
Section: 27 [input.output] Status: NAD Future Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2009-07-14
View all other issues in [input.output].
View all issues with NAD Future status.
Discussion:
A third party test suite tries to exercise istream::ignore(N) with a negative value of N and expects that the implementation will treat N as if it were 0. Our implementation asserts that (N >= 0) holds and aborts the test.
I can't find anything in section 27 that prohibits such values but I don't see what the effects of such calls should be, either (this applies to a number of unformatted input functions as well as some member functions of the basic_streambuf template).
[ 2009-07 Frankfurt ]
This is related to LWG 255.
Move to NAD Future.
Proposed resolution:
I propose that we add to each function in clause 27 that takes an argument, say N, of type streamsize a Requires clause saying that "N >= 0." The intent is to allow negative streamsize values in calls to precision() and width() but disallow it in calls to streambuf::sgetn(), istream::ignore(), or ostream::write().
[Kona: The LWG agreed that this is probably what we want. However, we need a review to find all places where functions in clause 27 take arguments of type streamsize that shouldn't be allowed to go negative. Martin will do that review.]
Section: 17.5.1.2 [structure.summary] Status: NAD Editorial Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2009-07-13
View all issues with NAD Editorial status.
Discussion:
The text in 17.3.1.1, p1 says:
"Paragraphs labelled "Note(s):" or "Example(s):" are informative, other
paragraphs are normative."
The library section makes heavy use of paragraphs labeled "Notes(s),"
some of which are clearly intended to be normative (see list 1), while
some others are not (see list 2). There are also those where the intent
is not so clear (see list 3).
List 1 -- Examples of (presumably) normative Notes:
20.8.5.1 [allocator.members], p3,
20.8.5.1 [allocator.members], p10,
21.4.2 [string.cons], p11,
22.3.1.2 [locale.cons], p11,
23.3.2.3 [deque.modifiers], p2,
25.4.7 [alg.min.max], p3,
26.4.6 [complex.ops], p15,
27.6.2.4.3 [streambuf.virt.get], p7.
List 2 -- Examples of (presumably) informative Notes:
18.6.1.3 [new.delete.placement], p3,
21.4.6.6 [string::replace], p14,
22.4.1.4.2 [locale.codecvt.virtuals], p3,
25.2.4 [alg.foreach], p4,
26.4.5 [complex.member.ops], p1,
27.5.2.5 [ios.base.storage], p6.
List 3 -- Examples of Notes that are not clearly either normative
or informative:
22.3.1.2 [locale.cons], p8,
22.3.1.5 [locale.statics], p6,
27.6.2.4.5 [streambuf.virt.put], p4.
None of these lists is meant to be exhaustive.
[Definitely a real problem. The big problem is there's material that doesn't quite fit any of the named paragraph categories (e.g. Effects). Either we need a new kind of named paragraph, or we need to put more material in unnamed paragraphs jsut after the signature. We need to talk to the Project Editor about how to do this. ]
[ Bellevue: Specifics of list 3: First 2 items correct in std (22.1.1.2, 22.1.1.5) Third item should be non-normative (27.5.2.4.5), which Pete will handle editorially. ]
[ post San Francisco: Howard: reopened, needs attention. ]
[Pete: I changed the paragraphs marked "Note" and "Notes" to use "Remark" and "Remarks". Fixed as editorial. This change has been in the WD since the post-Redmond mailing, in 2004. Recommend NAD.]
[ Batavia: We feel that the references in List 2 above should be changed from Remarks to Notes. We also feel that those items in List 3 need to be double checked for the same change. Alan and Pete to review. ]
[ Batavia (2009-05): ]
A spot-check of List 2 suggests the issue is still relevant, and a review of List 3 still seems called-for.
Move to NAD Editorial.
Proposed resolution:
Section: 27.5.4.3 [iostate.flags] Status: Dup Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2006-12-30
View all other issues in [iostate.flags].
View all issues with Dup status.
Duplicate of: 412
Discussion:
The Effects clause in 27.4.4.3, p5 describing the effects of a call to the ios_base member function clear(iostate state) says that the function only throws if the respective bits are already set prior to the function call. That's obviously not the intent. If it was, a call to clear(badbit) on an object for which (rdstate() == goodbit && exceptions() == badbit) holds would not result in an exception being thrown.
Proposed resolution:
The text ought to be changed from
"If (rdstate() & exceptions()) == 0, returns. ..."
to
"If (state & exceptions()) == 0, returns. ..."
Rationale:
Section: 18.8.2.4 [unexpected] Status: NAD Submitter: Vyatcheslav Sysoltsev Opened: 2003-09-29 Last modified: 2006-12-27
View all issues with NAD status.
Discussion:
Clause 15.5.2 [except.unexpected] paragraph 1 says that "void unexpected(); is called (18.7.2) immediately after completing the stack unwinding for the former function", but 18.7.2.4 (Effects) says that "void unexpected(); . . . Calls the unexpected_handler function in effect immediately after evaluating the throwexpression (18.7.2.2),". Isn't here a contradiction: 15.5.2 requires stack have been unwound when in void unexpected() and therefore in unexpected_handler but 18.7.2.4 claims that unexpected_handler is called "in effect immediately" after evaluation of throw expression is finished, so there is no space left for stack to be unwound therefore? I think the phrase "in effect immediately" should be removed from the standard because it brings ambiguity in understanding.
Proposed resolution:
Rationale:
There is no contradiction. The phrase "in effect immediately" is just to clarify which handler is to be called.
Section: 27.7.2.6.2 [ostream.inserters.arithmetic] Status: NAD Submitter: Ivan Godard Opened: 2003-10-24 Last modified: 2006-12-27
View all other issues in [ostream.inserters.arithmetic].
View all issues with NAD status.
Discussion:
Given:
void f(int) {}
void(*g)(int) = f;
cout << g;
(with the expected #include and usings), the value printed is a rather surprising "true". Rather useless too.
The standard defines:
ostream& operator<<(ostream&, void*);
which picks up all data pointers and prints their hex value, but does not pick up function pointers because there is no default conversion from function pointer to void*. Absent that, we fall back to legacy conversions from C and the function pointer is converted to bool.
There should be an analogous inserter that prints the address of a function pointer.
Proposed resolution:
Rationale:
This is indeed a wart, but there is no good way to solve it. C doesn't provide a portable way of outputting the address of a function point either.
Section: 22.4 [locale.categories] Status: NAD Submitter: Matt Austern Opened: 2003-11-02 Last modified: 2006-12-27
View all other issues in [locale.categories].
View all issues with NAD status.
Discussion:
The following facets classes have no copy constructors described in the standard, which, according to the standard, means that they are supposed to use the compiler-generated defaults. Default copy behavior is probably inappropriate. We should either make these classes uncopyable or else specify exactly what their constructors do.
Related issue: 421.
ctype_base
ctype
ctype_byname
ctype<char>
ctype_byname<char>
codecvt_base
codecvt
codecvt_byname
num_get
num_put
numpunct
numpunct_byname
collate
collate_byname
time_base
time_get
time_get_byname
time_put
time_put_byname
money_get
money_put
money_base
moneypunct
moneypunct_byname
messages_base
messages
messages_byname
Proposed resolution:
Rationale:
The copy constructor in the base class is private.
Section: 26.4.8 [complex.transcendentals] Status: NAD Submitter: Matt Austern Opened: 2003-11-05 Last modified: 2009-03-21
View all issues with NAD status.
Discussion:
Operations like pow and exp on complex<T> are typically implemented in terms of operations like sin and cos on T. Should implementations write this as std::sin, or as plain unqualified sin?
The issue, of course, is whether we want to use argument-dependent lookup in the case where T is a user-defined type. This is similar to the issue of valarray transcendentals, as discussed in issue 226.
This issue differs from valarray transcendentals in two important ways. First, "the effect of instantiating the template complex for types other than float, double or long double is unspecified." (26.4.1 [complex.syn]) Second, the standard does not dictate implementation, so there is no guarantee that a particular real math function is used in the implementation of a particular complex function.
Proposed resolution:
Rationale:
If you instantiate std::complex for user-defined types, all bets are off.
Section: 22.3.1.1.1 [locale.category] Status: Dup Submitter: Pete Becker Opened: 2003-12-26 Last modified: 2007-01-15
View all other issues in [locale.category].
View all issues with Dup status.
Duplicate of: 327
Discussion:
22.1.1.1.1/4, table 52, "Required Instantiations", lists, among others:
time_get<char,InputIterator>
time_get_byname<char,InputIterator>
time_get<wchar_t,OutputIterator>
time_get_byname<wchar_t,OutputIterator>
The second argument to the last two should be InputIterator, not OutputIterator.
Proposed resolution:
Change the second template argument to InputIterator.
Rationale:
Section: 23.4.3 [set] Status: Dup Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2009-05-01
View all other issues in [set].
View all issues with Dup status.
Duplicate of: 214
Discussion:
map/multimap have:
iterator find(const key_type& x) const;
const_iterator find(const key_type& x) const;
which is consistent with the table of associative container requirements. But set/multiset have:
iterator find(const key_type&) const;
set/multiset should look like map/multimap, and honor the requirements table, in this regard.
Proposed resolution:
Rationale:
Section: 23.2.4 [associative.reqmts], 23.4 [associative] Status: Dup Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2009-05-01
View other active issues in [associative.reqmts].
View all other issues in [associative.reqmts].
View all issues with Dup status.
Duplicate of: 130
Discussion:
map/multimap/set/multiset have:
void erase(iterator);
void erase(iterator, iterator);
But there's no good reason why these can't return an iterator, as for vector/deque/list:
iterator erase(iterator);
iterator erase(iterator, iterator);
Proposed resolution:
Informally: The table of associative container requirements, and the relevant template classes, should return an iterator designating the first element beyond the erased subrange.
Rationale:
Section: 22.3.1.3 [locale.members] Status: NAD Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2009-05-01
View all other issues in [locale.members].
View all issues with NAD status.
Discussion:
template<class Facet>
locale::combine(const locale&) const;
is obliged to create a locale that has no name. This is overspecification and overkill. The resulting locale should follow the usual rules -- it has a name if the locale argument has a name and Facet is one of the standard facets.
[ Sydney and post-Sydney (see c++std-lib-13439, c++std-lib-13440, c++std-lib-13443): agreed that it's overkill to say that the locale is obligated to be nameless. However, we also can't require it to have a name. At the moment, locale names are based on categories and not on individual facets. If a locale contains two different facets of different names from the same category, then this would not fit into existing naming schemes. We need to give implementations more freedom. Bill will provide wording. ]
Rationale:
After further discussion the LWG decided to close this as NAD. The fundamental problem is that names right now are per-category, not per-facet. The combine member function works at the wrong level of granularity.
Section: 27.9.1.4 [filebuf.members] Status: NAD Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2009-05-01
View all other issues in [filebuf.members].
View all issues with NAD status.
Duplicate of: 105
Discussion:
basic_filebuf *basic_filebuf::open(const char *, ios_base::open_mode);
should be supplemented with the overload:
basic_filebuf *basic_filebuf::open(const wchar_t *, ios_base::open_mode);
Depending on the operating system, one of these forms is fundamental and the other requires an implementation-defined mapping to determine the actual filename.
[Sydney: Yes, we want to allow wchar_t filenames. Bill will provide wording.]
[ In Toronto we noted that this is issue 5 from N1569. ]
How does this interact with the newly-defined character types, and how do we avoid interface explosion considering std::string overloads that were added? Propose another solution that is different than the suggestion proposed by PJP.
Suggestion is to make a member template function for basic_string (for char, wchar_t, u16char, u32char instantiations), and then just keep a const char* member.
Goal is to do implicit conversion between character string literals to appropriate basic_string type. Not quite sure if this is possible.
Implementors are free to add specific overloads for non-char character types.
[ Martin adds pre-Sophia Antipolis: ]
Please see issue 454: problems and solutions.
[ Sophia Antipolis: ]
Beman is concerned that making these changes to basic_filebuf is not usefully changed unless fstream is also changed; this also only handles wchar_t and not other character types.
The TR2 filesystem library is a more complete solution, but is not available soon.
[ Martin adds: please reference N2683 for problems and solutions. ]
Proposed resolution:
Change from:
basic_filebuf<charT,traits>* open( const char* s, ios_base::openmode mode );Effects: If is_open() != false, returns a null pointer. Otherwise, initializes the filebuf as required. It then opens a file, if possible, whose name is the NTBS s ("as if" by calling std::fopen(s,modstr)).
to:
basic_filebuf<charT,traits>* open( const char* s, ios_base::openmode mode ); basic_filebuf<charT,traits>* open( const wchar_t* ws, ios_base::openmode mode );Effects: If is_open() != false, returns a null pointer. Otherwise, initializes the filebuf as required. It then opens a file, if possible, whose name is the NTBS s ("as if" by calling std::fopen(s,modstr)). For the second signature, the NTBS s is determined from the WCBS ws in an implementation-defined manner.
(NOTE: For a system that "naturally" represents a filename as a WCBS, the NTBS s in the first signature may instead be mapped to a WCBS; if so, it follows the same mapping rules as the first argument to open.)
Rationale:
Slightly controversial, but by a 7-1 straw poll the LWG agreed to move this to Ready. The controversy was because the mapping between wide names and files in a filesystem is implementation defined. The counterargument, which most but not all LWG members accepted, is that the mapping between narrow files names and files is also implemenation defined.
[Lillehammer: Moved back to "open" status, at Beman's urging. (1) Why just basic_filebuf, instead of also basic_fstream (and possibly other things too). (2) Why not also constructors that take std::basic_string? (3) We might want to wait until we see Beman's filesystem library; we might decide that it obviates this.]
[ post Bellevue: ]
Move again to Ready.
There is a timing issue here. Since the filesystem library will not be in C++0x, this should be brought forward. This solution would remain valid in the context of the proposed filesystem.
This issue has been kicking around for a while, and the wchar_t addition alone would help many users. Thus, we suggest putting this on the reflector list with an invitation for someone to produce proposed wording that covers basic_fstream. In the meantime, we suggest that the proposed wording be adopted as-is.
If more of the Lillehammer questions come back, they should be introduced as separate issues.
[ San Francisco: ]
Some existing implementations provide overload already. Expected filesystem "path" object overloads neatly, without surprises; implying NAD.
Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: NAD Submitter: Martin Sebor Opened: 2004-03-16 Last modified: 2009-07-14
View other active issues in [facet.num.get.virtuals].
View all other issues in [facet.num.get.virtuals].
View all issues with NAD status.
Discussion:
When parsing strings of wide-character digits, the standard requires the library to widen narrow-character "atoms" and compare the widened atoms against the characters that are being parsed. Simply narrowing the wide characters would be far simpler, and probably more efficient. The two choices are equivalent except in convoluted test cases, and many implementations already ignore the standard and use narrow instead of widen.
First, I disagree that using narrow() instead of widen() would necessarily have unfortunate performance implications. A possible implementation of narrow() that allows num_get to be implemented in a much simpler and arguably comparably efficient way as calling widen() allows, i.e. without making a virtual call to do_narrow every time, is as follows:
inline char ctype<wchar_t>::narrow (wchar_t wc, char dflt) const
{
const unsigned wi = unsigned (wc);
if (wi > UCHAR_MAX)
return typeid (*this) == typeid (ctype<wchar_t>) ?
dflt : do_narrow (wc, dflt);
if (narrow_ [wi] < 0) {
const char nc = do_narrow (wc, dflt);
if (nc == dflt)
return dflt;
narrow_ [wi] = nc;
}
return char (narrow_ [wi]);
}
Second, I don't think the change proposed in the issue (i.e., to use narrow() instead of widen() during Stage 2) would be at all drastic. Existing implementations with the exception of libstdc++ currently already use narrow() so the impact of the change on programs would presumably be isolated to just a single implementation. Further, since narrow() is not required to translate alternate wide digit representations such as those mentioned in issue 303 to their narrow equivalents (i.e., the portable source characters '0' through '9'), the change does not necessarily imply that these alternate digits would be treated as ordinary digits and accepted as part of numbers during parsing. In fact, the requirement in 22.4.1.1.2 [locale.ctype.virtuals], p13 forbids narrow() to translate an alternate digit character, wc, to an ordinary digit in the basic source character set unless the expression (ctype<charT>::is(ctype_base::digit, wc) == true) holds. This in turn is prohibited by the C standard (7.25.2.1.5, 7.25.2.1.5, and 5.2.1, respectively) for charT of either char or wchar_t.
[Sydney: To a large extent this is a nonproblem. As long as you're only trafficking in char and wchar_t we're only dealing with a stable character set, so you don't really need either 'widen' or 'narrow': can just use literals. Finally, it's not even clear whether widen-vs-narrow is the right question; arguably we should be using codecvt instead.]
[ 2009-07 Frankfurt ]
NAD. The standard is clear enough as written.
Proposed resolution:
Change stage 2 so that implementations are permitted to use either technique to perform the comparison:
Section: 3.6.3 [basic.start.term], 18.4 [cstdint] Status: NAD Submitter: Bill Plauger Opened: 2004-03-23 Last modified: 2008-02-25
View all issues with NAD status.
Discussion:
3.6.3 Termination spells out in detail the interleaving of static destructor calls and calls to functions registered with atexit. To match this behavior requires intimate cooperation between the code that calls destructors and the exit/atexit machinery. The former is tied tightly to the compiler; the latter is a primitive mechanism inherited from C that traditionally has nothing to do with static construction and destruction. The benefits of intermixing destructor calls with atexit handler calls is questionable at best, and very difficult to get right, particularly when mixing third-party C++ libraries with different third-party C++ compilers and C libraries supplied by still other parties.
I believe the right thing to do is defer all static destruction until after all atexit handlers are called. This is a change in behavior, but one that is likely visible only to perverse test suites. At the very least, we should permit deferred destruction even if we don't require it.
[If this is to be changed, it should probably be changed by CWG. At this point, however, the LWG is leaning toward NAD. Implementing what the standard says is hard work, but it's not impossible and most vendors went through that pain years ago. Changing this behavior would be a user-visible change, and would break at least one real application.]
[ Batavia: Send to core with our recommendation that we should permit deferred destruction but not require it. ]
[ Howard: The course of action recommended in Batavia would undo LWG issue 3 and break current code implementing the "phoenix singleton". Search the net for "phoenix singleton atexit" to get a feel for the size of the adverse impact this change would have. Below is sample code which implements the phoenix singleton and would break if atexit is changed in this way: ]
#include <cstdlib>
#include <iostream>
#include <type_traits>
#include <new>
class A
{
bool alive_;
A(const A&);
A& operator=(const A&);
public:
A() : alive_(true) {std::cout << "A()\n";}
~A() {alive_ = false; std::cout << "~A()\n";}
void use()
{
if (alive_)
std::cout << "A is alive\n";
else
std::cout << "A is dead\n";
}
};
void deallocate_resource();
// This is the phoenix singleton pattern
A& get_resource(bool create = true)
{
static std::aligned_storage<sizeof(A), std::alignment_of<A>::value>::type buf;
static A* a;
if (create)
{
if (a != (A*)&buf)
{
a = ::new (&buf) A;
std::atexit(deallocate_resource);
}
}
else
{
a->~A();
a = (A*)&buf + 1;
}
return *a;
}
void deallocate_resource()
{
get_resource(false);
}
void use_A(const char* message)
{
A& a = get_resource();
std::cout << "Using A " << message << "\n";
a.use();
}
struct B
{
~B() {use_A("from ~B()");}
};
B b;
int main()
{
use_A("from main()");
}
The correct output is:
A() Using A from main() A is alive ~A() A() Using A from ~B() A is alive ~A()
[ Bellevue: Confirmed no interaction with quick_exit. Strong feeling against mandating the change. Leaning towards NAD rather than permitting the change, as this would make common implementations of pheonix-singleton pattern implementation defined, as noted by Howard. Bill agrees issue is no longer serious, and accepts NAD. ]
Proposed resolution:
Section: 21.4.1 [string.require] Status: NAD Submitter: Daniel Frey Opened: 2004-06-10 Last modified: 2009-07-14
View all other issues in [string.require].
View all issues with NAD status.
Discussion:
Today, my colleagues and me wasted a lot of time. After some time, I found the problem. It could be reduced to the following short example:
#include <string>
int main() { std::string( 0 ); }
The problem is that the tested compilers (GCC 2.95.2, GCC 3.3.1 and Comeau online) compile the above without errors or warnings! The programs (at least for the GCC) resulted in a SEGV.
I know that the standard explicitly states that the ctor of string requires a char* which is not zero. STLs could easily detect the above case with a private ctor for basic_string which takes a single 'int' argument. This would catch the above code at compile time and would not ambiguate any other legal ctors.
[Redmond: No great enthusiasm for doing this. If we do, however, we want to do it for all places that take charT* pointers, not just the single-argument constructor. The other question is whether we want to catch this at compile time (in which case we catch the error of a literal 0, but not an expression whose value is a null pointer), at run time, or both. Recommend NAD. Relegate this functionality to debugging implementations.]
[ Post Summit: Alisdair requests this be re-opened as several new language facilities are designed to solve exactly this kind of problem. ]
[ Batavia (2009-05): ]
We are unable to achieve consensus on an approach to a resolution. There is some sentiment for treating this as a QOI matter. It is also possible that when string is brought into the concepts world, this issue might be addressed in that context.
[ 2009-07 Frankfurt ]
We considered three options:
- The proposed resolution.
- NAD
- Interpret a null pointer as the empty string.
The consensus was NAD.
Proposed resolution:
Add to the synopsis in 21.4 [basic.string]
basic_string( nullptr_t ) = delete;
Section: 23 [containers] Status: NAD Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2007-04-18
View other active issues in [containers].
View all other issues in [containers].
View all issues with NAD status.
Discussion:
The standard doesn't prohibit the destructors (or any other special functions) of containers' elements invoked from a member function of the container from "recursively" calling the same (or any other) member function on the same container object, potentially while the container is in an intermediate state, or even changing the state of the container object while it is being modified. This may result in some surprising (i.e., undefined) behavior.
Read email thread starting with c++std-lib-13637 for more.
Proposed resolution:
Add to Container Requirements the following new paragraph:
Unless otherwise specified, the behavior of a program that
invokes a container member function f from a member function
g of the container's value_type on a container object c that
called g from its mutating member function h, is undefined.
I.e., if v is an element of c, directly or indirectly calling
c.h() from v.g() called from c.f(), is undefined.
[Redmond: This is a real issue, but it's probably a clause 17 issue, not clause 23. We get the same issue, for example, if we try to destroy a stream from one of the stream's callback functions.]
Rationale:
Recommend NAD. We agree this is an issue, but not a defect. We believe that there is no wording we can put in the standard that will cover all cases without introducing unfortunate corner cases.
Section: 25.4.3.3 [equal.range] Status: Dup Submitter: Prateek R Karandikar Opened: 2004-06-30 Last modified: 2006-12-30
View all other issues in [equal.range].
View all issues with Dup status.
Duplicate of: 270
Discussion:
There is no "Returns:" clause for std::equal_range, which returns non-void.
Proposed resolution:
Rationale:
Fixed as part of issue 270.
Section: 24.2.3 [forward.iterators] Status: NAD Submitter: Dave Abrahams Opened: 2004-07-09 Last modified: 2007-01-15
View all other issues in [forward.iterators].
View all issues with NAD status.
Discussion:
24.1/3 says:
Forward iterators satisfy all the requirements of the input and output iterators and can be used whenever either kind is specified
The problem is that satisfying the requirements of output iterator means that you can always assign *something* into the result of dereferencing it. That makes almost all non-mutable forward iterators non-conforming. I think we need to sever the refinement relationship between forward iterator and output iterator.
Related issue: 200. But this is not a dup.
Proposed resolution:
Rationale:
Yes, 24.1/3 does say that. But it's introductory material. The precise specification is in 24.1.3, and the requrements table there is right. We don't need to fine-tune introductory wording. (Especially since this wording is likely to be changed as part of the iterator overhaul.)
Section: 24.2.3 [forward.iterators] Status: Dup Submitter: Dave Abrahams Opened: 2004-07-11 Last modified: 2007-01-15
View all other issues in [forward.iterators].
View all issues with Dup status.
Duplicate of: 478
Discussion:
The Forward Iterator requirements table contains the following:
expression return type operational precondition
semantics
========== ================== =========== ==========================
a->m U& if X is mutable, (*a).m pre: (*a).m is well-defined.
otherwise const U&
r->m U& (*r).m pre: (*r).m is well-defined.
The first line is exactly right. The second line is wrong. Basically it implies that the const-ness of the iterator affects the const-ness of referenced members. But Paragraph 11 of [lib.iterator.requirements] says:
In the following sections, a and b denote values of type const X, n denotes a value of the difference type Distance, u, tmp, and m denote identifiers, r denotes a value of X&, t denotes a value of value type T, o denotes a value of some type that is writable to the output iterator.
AFAICT if we need the second line at all, it should read the same as the first line.
Related issue: 478
Proposed resolution:
Rationale:
The LWG agrees that this is a real problem. Marked as a DUP because the LWG chose to adopt the solution proposed in 478.
Section: 23.2 [container.requirements] Status: Dup Submitter: Herb Sutter Opened: 2004-08-01 Last modified: 2007-04-18
View other active issues in [container.requirements].
View all other issues in [container.requirements].
View all issues with Dup status.
Duplicate of: 580
Discussion:
Nothing in the standard appears to make this program ill-formed:
struct C {
void* operator new( size_t s ) { return ::operator new( s ); }
// NOTE: this hides in-place and nothrow new
};
int main() {
vector<C> v;
v.push_back( C() );
}
Is that intentional? We should clarify whether or not we intended to require containers to support types that define their own special versions of operator new.
[ Lillehammer: A container will definitely never use this overridden operator new, but whether it will fail to compile is unclear from the standard. Are containers supposed to use qualified or unqualified placement new? 20.4.1.1 is somewhat relevant, but the standard doesn't make it completely clear whether containers have to use Allocator::construct(). If containers don't use it, the details of how containers use placement new are unspecified. That is the real bug, but it needs to be fixed as part of the allocator overhaul. Weak support that the eventual solution should make this code well formed. ]
Proposed resolution:
Section: 20.7.3 [base] Status: NAD Submitter: Joe Gottman Opened: 2004-08-19 Last modified: 2006-12-29
View all other issues in [base].
View all issues with NAD status.
Discussion:
The classes std::unary_function and std::binary_function are both designed to be inherited from but contain no virtual functions. This makes it too easy for a novice programmer to write code like binary_function<int, int, int> *p = new plus<int>; delete p;
There are two common ways to prevent this source of undefined behavior: give the base class a public virtual destructor, or give it a protected nonvirtual destructor. Since unary_function and binary_function have no other virtual functions, (note in particular the absence of an operator()() ), it would cost too much to give them public virtual destructors. Therefore, they should be given protected nonvirtual destructors.
Proposed resolution:
Change Paragraph 20.3.1 of the Standard from
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
};
template <class Arg1, class Arg2, class Result>
struct binary_function {
typedef Arg1 first_argument_type;
typedef Arg2 second_argument_type;
typedef Result result_type;
};
to
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
protected:
~unary_function() {}
};
template <class Arg1, class Arg2, class Result>
struct binary_function {
typedef Arg1 first_argument_type;
typedef Arg2 second_argument_type;
typedef Result result_type;
protected:
~binary_function() {}
};
Rationale:
The LWG doesn't believe the existing definition causes anybody any concrete harm.
Section: 25.3.9 [alg.unique] Status: NAD Submitter: Andrew Koenig Opened: 2004-08-30 Last modified: 2006-12-27
View all other issues in [alg.unique].
View all issues with NAD status.
Discussion:
The standard says that unique(first, last) "eliminates all but the first element from every consecutive group of equal elements" in [first, last) and returns "the end of the resulting range". So a postcondition is that [first, result) is the same as the old [first, last) except that duplicates have been eliminated.
What postconditions are there on the range [result, last)? One might argue that the standard says nothing about those values, so they can be anything. One might also argue that the standard doesn't permit those values to be changed, so they must not be. Should the standard say something explicit one way or the other?
Proposed resolution:
Rationale:
We don't want to make many guarantees about what's in [result, end). Maybe we aren't being quite explicit enough about not being explicit, but it's hard to think that's a major problem.
Section: 20.3.3 [pairs], 20.5 [tuple] Status: NAD Editorial Submitter: Andrew Koenig Opened: 2004-09-14 Last modified: 2007-05-06
View other active issues in [pairs].
View all other issues in [pairs].
View all issues with NAD Editorial status.
Discussion:
(Based on recent comp.std.c++ discussion)
Pair (and tuple) should specialize std::swap to work in terms of std::swap on their components. For example, there's no obvious reason why swapping two objects of type pair<vector<int>, list<double> > should not take O(1).
[Lillehammer: We agree it should be swappable. Howard will provide wording.]
[ Post Oxford: We got swap for pair but accidently missed tuple. tuple::swap is being tracked by 522. ]
Proposed resolution:
Wording provided in N1856.
Rationale:
Recommend NAD, fixed by N1856.
Section: 25.2 [alg.nonmodifying], 25.3 [alg.modifying.operations] Status: Dup Submitter: Peter Dimov Opened: 2004-09-20 Last modified: 2007-01-15
View all issues with Dup status.
Duplicate of: 283
Discussion:
c++std-lib-14262
[lib.alg.find] requires T to be EqualityComparable:
template <class InputIterator, class T>
InputIterator find(InputIterator first, InputIterator last,
const T& value);
However the condition being tested, as specified in the Effects clause, is actually *i == value, where i is an InputIterator.
The two clauses are in agreement only if the type of *i is T, but this isn't necessarily the case. *i may have a heterogeneous comparison operator that takes a T, or a T may be convertible to the type of *i.
Further discussion (c++std-lib-14264): this problem affects a number of algorithsm in clause 25, not just find. We should try to resolve this problem everywhere it appears.
Proposed resolution:
[lib.alg.find]:
Remove [lib.alg.find]/1.
[lib.alg.count]:
Remove [lib.alg.count]/1.
[lib.alg.search]:
Remove "Type T is EqualityComparable (20.1.1), " from [lib.alg.search]/4.
[lib.alg.replace]:
Remove [lib.alg.replace]/1. Replace [lb.alg.replace]/2 with:
For every iterator i in the range [first, last) for which *i == value or pred(*i) holds perform *i = new_value.
Remove the first sentence of /4. Replace the beginning of /5 with:
For every iterator i in the range [result, result + (last - first)), assign to *i either...
(Note the defect here, current text says assign to i, not *i).
[lib.alg.fill]:
Remove "Type T is Assignable (23.1), " from /1. Replace /2 with:
For every iterator i in the range [first, last) or [first, first + n), perform *i = value.
[lib.alg.remove]:
Remove /1. Remove the first sentence of /6.
Rationale:
Duplicate of (a subset of) issue 283.
Section: 25.4.7 [alg.min.max] Status: Dup Submitter: Dave Abrahams Opened: 2004-10-13 Last modified: 2006-12-30
View all other issues in [alg.min.max].
View all issues with Dup status.
Duplicate of: 281
Discussion:
A straightforward implementation of these algorithms does not need to copy T.
Proposed resolution:
drop the the words "and CopyConstructible" from paragraphs 1 and 4
Rationale:
Section: 20.2.2 [allocator.requirements] Status: NAD Submitter: Dhruv Matani Opened: 2004-10-17 Last modified: 2006-12-30
View other active issues in [allocator.requirements].
View all other issues in [allocator.requirements].
View all issues with NAD status.
Discussion:
The standard's version of allocator::construct(pointer, const_reference) severely limits what you can construct using this function. Say you can construct a socket from a file descriptor. Now, using this syntax, I first have to manually construct a socket from the fd, and then pass the constructed socket to the construct() function so it will just to an uninitialized copy of the socket I manually constructed. Now it may not always be possible to copy construct a socket eh! So, I feel that the changes should go in the allocator::construct(), making it:
template<typename T>
struct allocator{
template<typename T1>
void construct(pointer T1 const& rt1);
};
Now, the ctor of the class T which matches the one that takes a T1 can be called! Doesn't that sound great?
Proposed resolution:
Rationale:
NAD. STL uses copying all the time, and making it possible for allocators to construct noncopyable objects is useless in the absence of corresponding container changes. We might consider this as part of a larger redesign of STL.
Section: 25.3.8 [alg.remove] Status: NAD Submitter: Thomas Mang Opened: 2004-12-12 Last modified: 2006-12-27
View all other issues in [alg.remove].
View all issues with NAD status.
Discussion:
In Section 25.2.7 [lib.alg.remove], paragraphs 1 to 5 describe the behavior of the mutating sequence operations std::remove and std::remove_if. However, the wording does not reflect the intended behavior [Note: See definition of intended behavior below] of these algorithms, as it is known to the C++ community [1].
1) Analysis of current wording:
25.2.7 [lib.alg.remove], paragraph 2:
Current wording says: "Effects: Eliminates all the elements referred to by iterator i in the range [first, last) for which the following corresponding conditions hold: *i == value, pred(*i) != false."
This sentences expresses specifically that all elements denoted by the (original) range [first, last) for which the corresponding condition hold will be eliminated. Since there is no formal definition of the term "eliminate" provided, the meaning of "eliminate" in everyday language implies that as postcondition, no element in the range denoted by [first, last) will hold the corresponding condition on reiteration over the range [first, last).
However, this is neither the intent [Note: See definition of intended behavior below] nor a general possible approach. It can be easily proven that if all elements of the original range[first, last) will hold the condition, it is not possible to substitute them by an element for which the condition will not hold.
25.2.7 [lib.alg.remove], paragraph 3:
Current wording says: "Returns: The end of the resulting range."
The resulting range is not specified. In combination with 25.2.7 [lib.alg.remove], paragraph 2, the only reasonable interpretation of this so-called resulting range is the range [first,last) - thus returning always the ForwardIterator 'last' parameter.
25.2.7 [lib.alg.remove], paragraph 4:
Current wording says: "Notes: Stable: the relative order of the elements that are not removed is the same as their relative order in the original range"
This sentences makes use of the term "removed", which is neither specified, nor used in a previous paragraph (which uses the term "eliminate"), nor unamgiuously separated from the name of the algorithm.
2) Description of intended behavior:
For the rest of this Defect Report, it is assumed that the intended behavior was that all elements of the range [first, last) which do not hold the condition *i == value (std::remove) or pred(*i) != false (std::remove_if)], call them s-elements [Note: s...stay], will be placed into a contiguous subrange of [first, last), denoted by the iterators [first, return value). The number of elements in the resulting range [first, return value) shall be equal to the number of s-elements in the original range [first, last). The relative order of the elements in the resulting subrange[first, return value) shall be the same as the relative order of the corresponding elements in the original range. It is undefined whether any elements in the resulting subrange [return value, last) will hold the corresponding condition, or not.
All implementations known to the author of this Defect Report comply with this intent. Since the intent of the behavior (contrary to the current wording) is also described in various utility references serving the C++ community [1], it is not expected that fixing the paragraphs will influence current code - unless the code relies on the behavior as it is described by current wording and the implementation indeed reflects the current wording, and not the intent.
3) Proposed fixes:
Change 25.2.7 [lib.alg.remove], paragraph 2 to:
"Effect: Places all the elements referred to by iterator i in the range [first, last) for which the following corresponding conditions hold : !(*i == value), pred(*i) == false into the subrange [first, k) of the original range, where k shall denote a value of type ForwardIterator. It is undefined whether any elements in the resulting subrange [k, last) will hold the corresponding condition, or not."
Comments to the new wording:
a) "Places" has no special meaning, and the everyday language meaning should fit. b) The corresponding conditions were negated compared to the current wording, becaue the new wording requires it. c) The wording "of the original range" might be redundant, since any subrange starting at 'first' and containing no more elements than the original range is implicitly a subrange of the original range [first, last). d) The iterator k was introduced instead of "return value" in order to avoid a cyclic dependency on 25.2.7/3. The wording ", where k shall denote a value of type ForwardIterator" might be redundant, because it follows implicitly by 25.2.7/3. e) "Places" does, in the author's opinion, explicitly forbid duplicating any element holding the corresponding condition in the original range [first, last) within the resulting range [first, k). If there is doubt this term might be not unambiguous regarding this, it is suggested that k is specified more closely by the following wording: "k shall denote a value of type ForwardIterator [Note: see d)] so that k - first is equal to the number of elements in the original range [first, last) for which the corresponding condition did hold". This could also be expressed as a separate paragraph "Postcondition:" f) The senctence "It is undefined whether any elements in the resulting subrange [k, last) will hold the corresponding condition, or not." was added consciously so the term "Places" does not imply if the original range [first, last) contains n elements holding the corresponding condition, the identical range[first, last) will also contain exactly n elements holding the corresponding condition after application of the algorithm.
Change 25.2.7 [lib.alg.remove], paragraph 3 to: "Returns: The iterator k."
Change 25.2.7 [lib.alg.remove], paragraph 4 to: "Notes: Stable: the relative order of the elements that are placed into the subrange [first, return value) shall be the same as their relative order was in the original range [first, last) prior to application of the algorithm."
Comments to the new wording:
a) the wording "was ... prior to application of the algorithm" is used to explicitly distinguish the original range not only by means of iterators, but also by a 'chronological' factor from the resulting range [first, return value). It might be redundant.
[1]: The wording of these references is not always unambiguous, and provided examples partially contradict verbal description of the algorithms, because the verbal description resembles the problematic wording of ISO/IEC 14882:2003.
Proposed resolution:
Rationale:
The LWG believes that the standard is sufficiently clear, and that there is no evidence of any real-world confusion about this point.
Section: 25.3.9 [alg.unique] Status: NAD Submitter: Thomas Mang Opened: 2004-12-12 Last modified: 2006-12-27
View all other issues in [alg.unique].
View all issues with NAD status.
Discussion:
In Section 25.2.8 [lib.alg.unique], paragraphs 1 to 3 describe the behavior of the mutating sequence operation std::unique. However, the wording does not reflect the intended behavior [Note: See definition of intended behavior below] of these algorithms, as it is known to the C++ community [1].
1) Analysis of current wording:
25.2.8 [lib.alg.unique], paragraph 1:
Current wording says: "Effects: Eliminates all but the first element from every consecutive group of equal elements referred to by the iterator i in the range [first, last) for which the following corresponding conditions hold: *i == *(i - 1) or pred(*i, *(i -1)) != false"
This sentences expresses specifically that all elements denoted by the (original) range [first, last) which are not but the first element from a consecutive group of equal elements (where equality is defined as *i == *(i - 1) or pred(*i, *(i - 1)) ! = false) [Note: See DR 202], call them r-elements [Note: r...remove], will be eliminated. Since there is no formal definition of the term "eliminate" provided, it is undefined how this "elimination" takes place. But the meaning of "eliminate" in everyday language seems to disallow explicitly that after application of the algorithm, any r-element will remain at any position of the range [first, last) [2].
Another defect in the current wording concerns the iterators used to compare two elements for equality: The current wording contains the expression "(i - 1)", which is not covered by 25/9 [Note: See DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions].
25.2.8 [lib.alg.unique], paragraph 2:
Current wording says: "Returns: The end of the resulting range."
The resulting range is not specified. In combination with 25.2.8 [lib.alg.unique], paragraph 1, one reasonable interpretation (in the author's opinion even the only possible interpretation) of this so-called resulting range is the range [first, last) - thus returning always the ForwardIterator 'last' parameter.
2) Description of intended behavior:
For the rest of this Defect Report, it is assumed that the intended behavior was that all elements denoted by the original range [first, last) which are the first element from a consecutive group of elements for which the corresponding conditions: *(i-1) == *i (for the version of unique without a predicate argument) or pred(*(i-1), *i) ! = false (for the version of unique with a predicate argument) [Note: If such a group of elements consists of only a single element, this is also considered the first element] [Note: See resolutions of DR 202], call them s-elements [Note: s...stay], will be placed into a contiguous subrange of [first, last), denoted by the iterators [first, return value). The number of elements in the resulting range [first, return value) shall be equal to the number of s-elements in the original range [first, last). Invalid iterator arithmetic expressions are expected to be resolved as proposed in DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions. It is also assumed by the author that the relative order of the elements in the resulting subrange [first, return value) shall be the same as the relative order of the corresponding elements (the s-elements) in the original range [Note: If this was not intended behavior, the additional proposed paragraph about stable order will certainly become obsolete]. Furthermore, the resolutions of DR 202 are partially considered.
All implementations known to the author of this Defect Report comply with this intent [Note: Except possible effects of DR 202]. Since this intent of the behavior (contrary to the current wording) is also described in various utility references serving the C++ community [1], it is not expected that fixing the paragraphs will influence current code [Note: Except possible effects of DR 202] - unless the code relies on the behavior as it is described by current wording and the implementation indeed reflects the current wording, and not the intent.
3) Proposed fixes:
Change 25.2.8 [lib.alg.unique], paragraph 1 to:
"Effect: Places the first element from every consecutive group of elements, referred to by the iterator i in the range [first, last), for which the following conditions hold: *(i-1) == *i (for the version of unique without a predicate argument) or pred(*(i -1), *i) != false (for the version of unique with a predicate argument), into the subrange [first, k) of the original range, where k shall denote a value of type ForwardIterator."
Comments to the new wording:
a) The new wording was influenced by the resolutions of DR 202. If DR 202 is resolved in another way, the proposed wording need also additional review. b) "Places" has no special meaning, and the everyday language meaning should fit. c) The expression "(i - 1)" was left, but is expected that DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions will take this into account. d) The wording "(for the version of unique without a predicate argument)" and "(for the version of unique with a predicate argument)" was added consciously for clarity and is in resemblence with current 23.2.2.4 [lib.list.ops], paragraph 19. It might be considered redundant. e) The wording "of the original range" might be redundant, since any subrange starting at first and containing no more elements than the original range is implicitly a subrange of the original range [first, last). f) The iterator k was introduced instead of "return value" in order to avoid a cyclic dependency on 25.2.8 [lib.alg.unique], paragraph 2. The wording ", where k shall denote a value of type ForwardIterator" might be redundant, because it follows implicitly by 25.2.8 [lib.alg.unique], paragraph 2. g) "Places" does, in the author's opinion, explicitly forbid duplicating any s-element in the original range [first, last) within the resulting range [first, k). If there is doubt this term might be not unambiguous regarding this, it is suggested that k is specified more closely by the following wording: "k shall denote a value of type ForwardIterator [Note: See f)] so that k - first is equal to the number of elements in the original range [first, last) being the first element from every consecutive group of elements for which the corresponding condition did hold". This could also be expressed as a separate paragraph "Postcondition:". h) If it is considered that the wording is unclear whether it declares the element of a group which consists of only a single element implicitly to be the first element of this group [Note: Such an interpretation could eventually arise especially in case last - first == 1] , the following additional sentence is proposed: "If such a group of elements consists of only a single element, this element is also considered the first element."
Change 25.2.8 [lib.alg.unique], paragraph 2 to: "Returns: The iterator k."
Add a separate paragraph "Notes:" as 25.2.8 [lib.alg.unique], paragraph 2a or 3a, or a separate paragraph "Postcondition:" before 25.2.8 [lib.alg.unique], paragraph 2 (wording inside {} shall be eliminated if the preceding expressions are used, or the preceding expressions shall be eliminated if wording inside {} is used):
"Notes:{Postcondition:} Stable: the relative order of the elements that are placed into the subrange [first, return value {k}) shall be the same as their relative order was in the original range [first, last) prior to application of the algorithm."
Comments to the new wording:
a) It is assumed by the author that the algorithm was intended to be stable. In case this was not the intent, this paragraph becomes certainly obsolete. b) The wording "was ... prior to application of the algorithm" is used to explicitly distinguish the original range not only by means of iterators, but also by a 'chronological' factor from the resulting range [first, return value). It might be redundant.
25.2.8 [lib.alg.unique], paragraph 3:
See DR 239.
4) References to other DRs:
See DR 202, but which does not address any of the problems described in this Defect Report [Note: This DR is supposed to complement DR 202]. See DR 239. See DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions.
[1]: The wording of these references is not always unambiguous, and provided examples partially contradict verbal description of the algorithms, because the verbal description resembles the problematic wording of ISO/IEC 14882:2003.
[2]: Illustration of conforming implementations according to current wording:
One way the author of this DR considers how this "elimination" could be achieved by a conforming implementation according to current wording is by substituting each r-element by _any_ s-element [Note: s...stay; any non-r-element], since all r-elements are "eliminated".
In case of a sequence consisting of elements being all 'equal' [Note: See DR 202], substituting each r-element by the single s-element is the only possible solution according to current wording.
Proposed resolution:
Rationale:
The LWG believes the standard is sufficiently clear. No implementers get it wrong, and changing it wouldn't cause any code to change, so there is no real-world harm here.
Section: 23.3.4.4 [list.ops] Status: NAD Submitter: Thomas Mang Opened: 2004-12-12 Last modified: 2007-02-19
View other active issues in [list.ops].
View all other issues in [list.ops].
View all issues with NAD status.
Discussion:
In Section 23.3.4.4 [list.ops], paragraphs 19 to 21 describe the behavior of the std::list<T, Allocator>::unique operation. However, the current wording is defective for various reasons.
1) Analysis of current wording:
23.3.4.4 [list.ops], paragraph 19:
Current wording says: "Effects: Eliminates all but the first element from every consecutive group of equal elements referred to by the iterator i in the range [first + 1, last) for which *i == *(i - 1) (for the version of unique with no argument) or pred(*i, *(i -1)) (for the version of unique with a predicate argument) holds."
This sentences makes use of the undefined term "Eliminates". Although it is, to a certain degree, reasonable to consider the term "eliminate" synonymous with "erase", using "Erase" in the first place, as the wording of 23.3.4.4 [list.ops], paragraph 15 does, would be clearer.
The range of the elements referred to by iterator i is "[first + 1, last)". However, neither "first" nor "last" is defined.
The sentence makes three times use of iterator arithmetic expressions ( "first + 1", "*i == *(i - 1)", "pred(*i, *(i -1))" ) which is not defined for bidirectional iterator [see DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions].
The same problems as pointed out in DR 202 (equivalence relation / order of arguments for pred()) apply to this paragraph.
23.3.4.4 [list.ops], paragraph 20:
Current wording says: "Throws: Nothing unless an exception in thrown by *i == *(i-1) or pred(*i, *(i - 1))"
The sentence makes two times use of invalid iterator arithmetic expressions ( "*i == *(i - 1)", "pred(*i, *(i -1))" ).
[Note: Minor typos: "in" / missing dot at end of sentence.]
23.3.4.4 [list.ops], paragraph 21:
Current wording says: "Complexity: If the range (last - first) is not empty, exactly (last - first) - 1 applications of the corresponding predicate, otherwise no application of the predicate.
See DR 315 regarding "(last - first)" not yielding a range.
Invalid iterator arithmetic expression "(last - first) - 1" left .
2) Description of intended behavior:
For the rest of this Defect Report, it is assumed that "eliminate" is supposed to be synonymous to "erase", that "first" is equivalent to an iterator obtained by a call to begin(), "last" is equivalent to an iterator obtained by a call to end(), and that all invalid iterator arithmetic expressions are resolved as described in DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions.
Furthermore, the resolutions of DR 202 are considered regarding equivalence relation and order of arguments for a call to pred.
All implementations known to the author of this Defect Report comply with these assumptions, apart from the impact of the alternative resolution of DR 202. Except for the changes implied by the resolutions of DR 202, no impact on current code is expected.
3) Proposed fixes:
Change 23.3.4.4 [list.ops], paragraph 19 to:
"Effect: Erases all but the first element from every consecutive group of elements, referred to by the iterator i in the range [begin(), end()), for which the following conditions hold: *(i-1) == *i (for the version of unique with no argument) or pred(*(i-1), *i) != false (for the version of unique with a predicate argument)."
Comments to the new wording:
a) The new wording was influenced by DR 202 and the resolutions presented there. If DR 202 is resolved in another way, the proposed wording need also additional review. b) "Erases" refers in the author's opinion unambiguously to the member function "erase". In case there is doubt this might not be unamgibuous, a direct reference to the member function "erase" is suggested [Note: This would also imply a change of 23.3.4.4 [list.ops], paragraph 15.]. c) The expression "(i - 1)" was left, but is expected that DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions will take this into account. d) The wording "(for the version of unique with no argument)" and "(for the version of unique with a predicate argument)" was kept consciously for clarity. e) "begin()" substitutes "first", and "end()" substitutes "last". The range need adjustment from "[first + 1, last)" to "[begin(), end())" to ensure a valid range in case of an empty list. f) If it is considered that the wording is unclear whether it declares the element of a group which consists of only a single element implicitly to be the first element of this group [Note: Such an interpretation could eventually arise especially in case size() == 1] , the following additional sentence is proposed: "If such a group of elements consists of only a single element, this element is also considered the first element."
Change 23.3.4.4 [list.ops], paragraph 20 to:
"Throws: Nothing unless an exception is thrown by *(i-1) == *i or pred(*(i-1), *i)."
Comments to the new wording:
a) The wording regarding the conditions is identical to proposed 23.3.4.4 [list.ops], paragraph 19. If 23.3.4.4 [list.ops], paragraph 19 is resolved in another way, the proposed wording need also additional review. b) The expression "(i - 1)" was left, but is expected that DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions will take this into account. c) Typos fixed.
Change 23.3.4.4 [list.ops], paragraph 21 to:
"Complexity: If empty() == false, exactly size() - 1 applications of the corresponding predicate, otherwise no applications of the corresponding predicate."
Comments to the new wording:
a) The new wording is supposed to also replace the proposed resolution of DR 315, which suffers from the problem of undefined "first" / "last".
5) References to other DRs:
See DR 202. See DR 239. See DR 315. See DR submitted by Thomas Mang regarding invalid iterator arithmetic expressions.
Proposed resolution:
Rationale:
"All implementations known to the author of this Defect Report comply with these assumption", and "no impact on current code is expected", i.e. there is no evidence of real-world confusion or harm.
Section: 17.5.1.4 [structure.specifications] Status: NAD Submitter: Thomas Mang Opened: 2004-12-12 Last modified: 2009-07-15
View all other issues in [structure.specifications].
View all issues with NAD status.
Discussion:
Various clauses other than clause 25 make use of iterator arithmetic not supported by the iterator category in question. Algorithms in clause 25 are exceptional because of 25 [lib.algorithms], paragraph 9, but this paragraph does not provide semantics to the expression "iterator - n", where n denotes a value of a distance type between iterators.
1) Examples of current wording:
Current wording outside clause 25:
23.2.2.4 [lib.list.ops], paragraphs 19-21: "first + 1", "(i - 1)", "(last - first)" 23.3.1.1 [lib.map.cons], paragraph 4: "last - first" 23.3.2.1 [lib.multimap.cons], paragraph 4: "last - first" 23.3.3.1 [lib.set.cons], paragraph 4: "last - first" 23.3.4.1 [lib.multiset.cons], paragraph 4: "last - first" 24.4.1 [lib.reverse.iterators], paragraph 1: "(i - 1)"
[Important note: The list is not complete, just an illustration. The same issue might well apply to other paragraphs not listed here.]
None of these expressions is valid for the corresponding iterator category.
Current wording in clause 25:
25.1.1 [lib.alg.foreach], paragraph 1: "last - 1" 25.1.3 [lib.alg.find.end], paragraph 2: "[first1, last1 - (last2-first2))" 25.2.8 [lib.alg.unique], paragraph 1: "(i - 1)" 25.2.8 [lib.alg.unique], paragraph 5: "(i - 1)"
However, current wording of 25 [lib.algorithms], paragraph 9 covers neither of these four cases:
Current wording of 25 [lib.algorithms], paragraph 9:
"In the description of the algorithms operator + and - are used for some of the iterator categories for which they do not have to be defined. In these cases the semantics of a+n is the same as that of
{X tmp = a;
advance(tmp, n);
return tmp;
}
and that of b-a is the same as of return distance(a, b)"
This paragrpah does not take the expression "iterator - n" into account, where n denotes a value of a distance type between two iterators [Note: According to current wording, the expression "iterator - n" would be resolved as equivalent to "return distance(n, iterator)"]. Even if the expression "iterator - n" were to be reinterpreted as equivalent to "iterator + -n" [Note: This would imply that "a" and "b" were interpreted implicitly as values of iterator types, and "n" as value of a distance type], then 24.3.4/2 interfers because it says: "Requires: n may be negative only for random access and bidirectional iterators.", and none of the paragraphs quoted above requires the iterators on which the algorithms operate to be of random access or bidirectional category.
2) Description of intended behavior:
For the rest of this Defect Report, it is assumed that the expression "iterator1 + n" and "iterator1 - iterator2" has the semantics as described in current 25 [lib.algorithms], paragraph 9, but applying to all clauses. The expression "iterator1 - n" is equivalent to an result-iterator for which the expression "result-iterator + n" yields an iterator denoting the same position as iterator1 does. The terms "iterator1", "iterator2" and "result-iterator" shall denote the value of an iterator type, and the term "n" shall denote a value of a distance type between two iterators.
All implementations known to the author of this Defect Report comply with these assumptions. No impact on current code is expected.
3) Proposed fixes:
Change 25 [lib.algorithms], paragraph 9 to:
"In the description of the algorithms operator + and - are used for some of the iterator categories for which they do not have to be defined. In this paragraph, a and b denote values of an iterator type, and n denotes a value of a distance type between two iterators. In these cases the semantics of a+n is the same as that of
{X tmp = a;
advance(tmp, n);
return tmp;
}
,the semantics of a-n denotes the value of an iterator i for which the following condition holds: advance(i, n) == a, and that of b-a is the same as of return distance(a, b)".
Comments to the new wording:
a) The wording " In this paragraph, a and b denote values of an iterator type, and n denotes a value of a distance type between two iterators." was added so the expressions "b-a" and "a-n" are distinguished regarding the types of the values on which they operate. b) The wording ",the semantics of a-n denotes the value of an iterator i for which the following condition holds: advance(i, n) == a" was added to cover the expression 'iterator - n'. The wording "advance(i, n) == a" was used to avoid a dependency on the semantics of a+n, as the wording "i + n == a" would have implied. However, such a dependency might well be deserved. c) DR 225 is not considered in the new wording.
Proposed fixes regarding invalid iterator arithmetic expressions outside clause 25:
Either a) Move modified 25 [lib.algorithms], paragraph 9 (as proposed above) before any current invalid iterator arithmetic expression. In that case, the first sentence of 25 [lib.algorithms], paragraph 9, need also to be modified and could read: "For the rest of this International Standard, ...." / "In the description of the following clauses including this ...." / "In the description of the text below ..." etc. - anyways substituting the wording "algorithms", which is a straight reference to clause 25. In that case, 25 [lib.algorithms] paragraph 9 will certainly become obsolete. Alternatively, b) Add an appropiate paragraph similar to resolved 25 [lib.algorithms], paragraph 9, to the beginning of each clause containing invalid iterator arithmetic expressions. Alternatively, c) Fix each paragraph (both current wording and possible resolutions of DRs) containing invalid iterator arithmetic expressions separately.
5) References to other DRs:
See DR 225. See DR 237. The resolution could then also read "Linear in last - first".
[ Bellevue: ]
Keep open and ask Bill to provide wording.
[ 2009-05-09 Alisdair adds: ]
This issue is related to 997.
[ 2009-07 Frankfurt ]
Hinnant: this isn't going to change any user's code or any vendor's implementation.
No objection to "NAD without prejudice." If anyone proposes a resolution, the LWG will consider it.
Move to NAD.
Proposed resolution:
[Lillehammer: Minor issue, but real. We have a blanket statement about this in 25/11. But (a) it should be in 17, not 25; and (b) it's not quite broad enough, because there are some arithmetic expressions it doesn't cover. Bill will provide wording.]
Section: 24.2.1 [input.iterators] Status: NAD Submitter: Chris Jefferson Opened: 2004-12-13 Last modified: 2006-12-27
View all other issues in [input.iterators].
View all issues with NAD status.
Discussion:
1) In 24.1.1/3, the following text is currently present.
"Note: For input iterators, a==b does not imply ++a=++b (Equality does not guarantee the substitution property or referential transparency)."
However, when in Table 72, part of the definition of ++r is given as:
"pre: r is dereferenceable. post: any copies of the previous value of r are no longer required either to be dereferenceable ..."
While a==b does not imply that b is a copy of a, this statement should perhaps still be made more clear.
2) There are no changes to intended behaviour
3) This Note should be altered to say "Note: For input iterators a==b, when its behaviour is defined ++a==++b may still be false (Equality does not guarantee the substitution property or referential transparency).
Proposed resolution:
Rationale:
This is descriptive text, not normative, and the meaning is clear.
Section: 23.2.4 [associative.reqmts] Status: NAD Submitter: Hans B os Opened: 2004-12-19 Last modified: 2006-12-27
View other active issues in [associative.reqmts].
View all other issues in [associative.reqmts].
View all issues with NAD status.
Discussion:
According to [lib.associative.reqmts] table 69, the runtime comlexity of insert(p, t) and erase(q) can be done in amortized constant time.
It was my understanding that an associative container could be implemented as a balanced binary tree.
For inser(p, t), you 'll have to iterate to p's next node to see if t can be placed next to p. Furthermore, the insertion usually takes place at leaf nodes. An insert next to the root node will be done at the left of the root next node
So when p is the root node you 'll have to iterate from the root to its next node, which takes O(log(size)) time in a balanced tree.
If you insert all values with insert(root, t) (where root is the root of the tree before insertion) then each insert takes O(log(size)) time. The amortized complexity per insertion will be O(log(size)) also.
For erase(q), the normal algorithm for deleting a node that has no empty left or right subtree, is to iterate to the next (or previous), which is a leaf node. Then exchange the node with the next and delete the leaf node. Furthermore according to DR 130, erase should return the next node of the node erased. Thus erasing the root node, requires iterating to the next node.
Now if you empty a map by deleting the root node until the map is empty, each operation will take O(log(size)), and the amortized complexity is still O(log(size)).
The operations can be done in amortized constant time if iterating to the next node can be done in (non amortized) constant time. This can be done by putting all nodes in a double linked list. This requires two extra links per node. To me this is a bit overkill since you can already efficiently insert or erase ranges with erase(first, last) and insert(first, last).
Proposed resolution:
Rationale:
Only "amortized constant" in special circumstances, and we believe that's implementable. That is: doing this N times will be O(N), not O(log N).
Section: 25.4.1.2 [stable.sort] Status: NAD Editorial Submitter: Prateek Karandikar Opened: 2005-04-12 Last modified: 2008-03-13
View all issues with NAD Editorial status.
Discussion:
17.3.1.1 Summary
1 The Summary provides a synopsis of the category, and introduces the first-level subclauses. Each subclause also provides a summary, listing the headers specified in the subclause and the library entities provided in each header.
2 Paragraphs labelled "Note(s):" or "Example(s):" are informative, other paragraphs are normative.
So this means that a "Notes" paragraph wouldn't be normative.
25.3.1.2 stable_sort
template<class RandomAccessIterator> void stable_sort(RandomAccessIterat or first, RandomAccessIterator last); template<class RandomAccessIterator, class Compare> void stable_sort(RandomAccessIterat or first, RandomAccessIterator last, Compare comp);1 Effects: Sorts the elements in the range [first, last).
2 Complexity: It does at most N(log N)^2 (where N == last - first) comparisons; if enough extra memory is available, it is N log N.
3 Notes: Stable: the relative order of the equivalent elements is preserved.
The Notes para is informative, and nowhere else is stability mentioned above.
Also, I just searched for the word "stable" in my copy of the Standard. and the phrase "Notes: Stable: the relative order of the elements..." is repeated several times in the Standard library clauses for describing various functions. How is it that stability is talked about in the informative paragraph? Or am I missing something obvious?
Proposed resolution:
Rationale:
This change has already been made.
Section: 22.4.1.5 [locale.codecvt.byname] Status: NAD Submitter: Krzysztof Żelechowski Opened: 2005-05-24 Last modified: 2008-03-13
View all other issues in [locale.codecvt.byname].
View all issues with NAD status.
Discussion:
Contradiction.
Proposed resolution:
Section: 20.7.3 [base] Status: NAD Submitter: Me <anti_spam_email2003@yahoo.com> Opened: 2005-06-07 Last modified: 2008-03-13
View all other issues in [base].
View all issues with NAD status.
Discussion:
"For templates greater, less, greater_equal, and less_equal, the specializations for any pointer type yield a total order, even if the built-in operators <, >, <=, >= do not."
The standard should do much better than guarantee that these provide a total order, it should guarantee that it can be used to test if memory overlaps, i.e. write a portable memmove. You can imagine a platform where the built-in operators use a uint32_t comparison (this tests for overlap on this platform) but the less<T*> functor is allowed to be defined to use a int32_t comparison. On this platform, if you use std::less with the intent of making a portable memmove, comparison on an array that straddles the 0x7FFFFFFF/0x8000000 boundary can give incorrect results.
Proposed resolution:
Add a footnote to 20.5.3/8 saying:
Given a p1 and p2 such that p1 points to N objects of type T and p2 points to M objects of type T. If [p1,p1+N) does not overlap [p2,p2+M), less returns the same value when comparing all pointers in [p1,p1+N) to all pointers in [p2,p2+M). Otherwise, there is a value Q and a value R such that less returns the same value when comparing all pointers in [p1,p1+Q) to all pointers in [p2,p2+R) and an opposite value when comparing all pointers in [p1+Q,p1+N) to all pointers in [p2+R,p2+M). For the sake of completeness, the null pointer value (4.10) for T is considered to be an array of 1 object that doesn't overlap with any non-null pointer to T. less_equal, greater, greater_equal, equal_to, and not_equal_to give the expected results based on the total ordering semantics of less. For T of void, treat it as having similar semantics as T of char i.e. less<cv T*>(a, b) gives the same results as less<cv void*>(a, b) which gives the same results as less<cv char*>((cv char*)(cv void*)a, (cv char*)(cv void*)b).
I'm also thinking there should be a footnote to 20.5.3/1 saying that if A and B are similar types (4.4/4), comp<A>(a,b) returns the same value as comp<B>(a,b) (where comp is less, less_equal, etc.). But this might be problematic if there is some really funky operator overloading going on that does different things based on cv (that should be undefined behavior if somebody does that though). This at least should be guaranteed for all POD types (especially pointers) that use the built-in comparison operators.
Rationale:
less is already required to provide a strict weak ordering which is good enough to detect overlapping memory situations.
Section: 22.3.1.1.1 [locale.category] Status: NAD Submitter: Christopher Conrade Zseleghovski Opened: 2005-06-07 Last modified: 2009-07-15
View all other issues in [locale.category].
View all issues with NAD status.
Discussion:
Motivation:
This requirement seems obvious to me, it is the essence of code modularity. I have complained to Mr. Plauger that the Dinkumware library does not observe this principle but he objected that this behaviour is not covered in the standard.
[ 2009-07 Frankfurt ]
No objection to NAD, Fixed.
Move to NAD.
Proposed resolution:
Append the following point to 22.1.1.1.1:
6. The implementation of a facet of Table 52 parametrized with an InputIterator/OutputIterator should use that iterator only as character source/sink respectively. For a *_get facet, it means that the value received depends only on the sequence of input characters and not on how they are accessed. For a *_put facet, it means that the sequence of characters output depends only on the value to be formatted and not of how the characters are stored.
[ Berlin: Moved to Open, Need to clean up this area to make it clear locales don't have to contain open ended sets of facets. Jack, Howard, Bill. ]
Section: 22.4 [locale.categories] Status: NAD Submitter: P.J. Plauger Opened: 2005-06-20 Last modified: 2009-07-15
View all other issues in [locale.categories].
View all issues with NAD status.
Discussion:
a) In 22.2.1.1 para. 2 we refer to "the instantiations required in Table 51" to refer to the facet *objects* associated with a locale. And we almost certainly mean just those associated with the default or "C" locale. Otherwise, you can't switch to a locale that enforces a different mapping between narrow and wide characters, or that defines additional uppercase characters.
b) 22.2.1.5 para. 3 (codecvt) has the same issues.
c) 22.2.1.5.2 (do_unshift) is even worse. It *forbids* the generation of a homing sequence for the basic character set, which might very well need one.
d) 22.2.1.5.2 (do_length) likewise dictates that the default mapping between wide and narrow characters be taken as one-for-one.
e) 22.2.2 para. 2 (num_get/put) is both muddled and vacuous, as far as I can tell. The muddle is, as before, calling Table 51 a list of instantiations. But the constraint it applies seems to me to cover *all* defined uses of num_get/put, so why bother to say so?
f) 22.2.3.1.2 para. 1(do_decimal_point) says "The required instantiations return '.' or L'.'.) Presumably this means "as appropriate for the character type. But given the vague definition of "required" earlier, this overrules *any* change of decimal point for non "C" locales. Surely we don't want to do that.
g) 22.2.3.1.2 para. 2 (do_thousands_sep) says "The required instantiations return ',' or L','.) As above, this probably means "as appropriate for the character type. But this overrules the "C" locale, which requires *no* character ('\0') for the thousands separator. Even if we agree that we don't mean to block changes in decimal point or thousands separator, we should also eliminate this clear incompatibility with C.
h) 22.2.3.1.2 para. 2 (do_grouping) says "The required instantiations return the empty string, indicating no grouping." Same considerations as for do_decimal_point.
i) 22.2.4.1 para. 1 (collate) refers to "instantiations required in Table 51". Same bad jargon.
j) 22.2.4.1.2 para. 1 (do_compare) refers to "instantiations required in Table 51". Same bad jargon.
k) 22.2.5 para. 1 (time_get/put) uses the same muddled and vacuous as num_get/put.
l) 22.2.6 para. 2 (money_get/put) uses the same muddled and vacuous as num_get/put.
m) 22.2.6.3.2 (do_pos/neg_format) says "The instantiations required in Table 51 ... return an object of type pattern initialized to {symbol, sign, none, value}." This once again *overrides* the "C" locale, as well as any other locale."
3) We constrain the use_facet calls that can be made by num_get/put, so why don't we do the same for money_get/put? Or for any of the other facets, for that matter?
4) As an almost aside, we spell out when a facet needs to use the ctype facet, but several also need to use a codecvt facet and we don't say so.
[ Berlin: Bill to provide wording. ]
[ 2009-07 Frankfurt ]
No objection to NAD.
Move to NAD.
Proposed resolution:
Section: X [rand.req], TR1 5.1.1 [tr.rand.req] Status: NAD Editorial Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand.req].
View all issues with NAD Editorial status.
Discussion:
In [tr.rand.req], Paragraph 2 states that "... s is a value of integral type, g is an ... object returning values of unsigned integral type ..."
Proposed resolution:
In 5.1.1 [tr.rand.req], Paragraph 2 replace
... s is a value of integral type, g is an lvalue of a type other than X that defines a zero-argument function object returning values of
unsigned integraltype unsigned long int, ...
In 5.1.1 [tr.rand.seq], Table 16, replace in the line for X(s)
creates an engine with the initial internal state determined by static_cast<unsigned long>(s)
[ Mont Tremblant: Both s and g should be unsigned long. This should refer to the constructor signatures. Jens provided wording post Mont Tremblant. ]
[ Berlin: N1932 adopts the proposed resolution: see 26.3.1.3/1e and Table 3 row 2. Moved to Ready. ]
Rationale:
Jens: Just requiring X(unsigned long) still makes it possible for an evil library writer to also supply a X(int) that does something unexpected. The wording above requires that X(s) always performs as if X(unsigned long) would have been called. I believe that is sufficient and implements our intentions from Mont Tremblant. I see no additional use in actually requiring a X(unsigned long) signature. u.seed(s) is covered by its reference to X(s), same arguments.
[ Portland: Subsumed by N2111. ]
Section: 26.5 [rand], TR1 5.1.3 [tr.rand.var] Status: NAD Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand].
View all issues with NAD status.
Discussion:
Paragraph 3 requires that template argument U (which corresponds to template parameter Engine) satisfy all uniform random number generator requirements. However, there is no analogous requirement regarding the template argument that corresponds to template parameter Distribution. We believe there should be, and that it should require that this template argument satisfy all random distribution requirements.
Proposed resolution:
Consequence 1: Remove the precondition clauses [tr.rand.var]/16 and /18.
Consequence 2: Add max() and min() functions to those distributions that do not already have them.
[ Mont Tremblant: Jens reccommends NAD, min/max not needed everywhere. Marc supports having min and max to satisfy generic programming interface. ]
Rationale:
Berlin: N1932 makes this moot: variate_generator has been eliminated.
Section: 26.5.8.1 [rand.dist.uni], TR1 5.1.7.1 [tr.rand.dist.iunif] Status: NAD Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand.dist.uni].
View all issues with NAD status.
Discussion:
In [tr.rand.dist.iunif] the uniform_int distribution currently has a single template parameter, IntType, used as the input_type and as the result_type of the distribution. We believe there is no reason to conflate these types in this way.
Proposed resolution:
We recommend that there be a second template parameter to reflect the distribution's input_type, and that the existing first template parameter continue to reflect (solely) the result_type:
template< class IntType = int, UIntType = unsigned int >
class uniform_int
{
public:
// types
typedef UIntType input_type;
typedef IntType result_type;
[ Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been eliminated. ]
Section: 26.5.8.2 [rand.dist.bern], TR1 5.1.7.2 [tr.rand.dist.bern] Status: NAD Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all issues with NAD status.
Discussion:
In [tr.rand.dist.bern] the distribution currently requires;
typedef int input_type;
Proposed resolution:
We believe this is an unfortunate choice, and recommend instead:
typedef unsigned int input_type;
[ Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been eliminated. ]
Section: 26.5.8 [rand.dist], TR1 5.1.7.5 [tr.rand.dist.bin] Status: NAD Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand.dist].
View all issues with NAD status.
Discussion:
Unlike all other distributions in TR1, this binomial_distribution has an implementation-defined input_type. We believe this is an unfortunate choice, because it hinders users from writing portable code. It also hinders the writing of compliance tests. We recommend instead:
typedef RealType input_type;
While this choice is somewhat arbitrary (as it was for some of the other distributions), we make this particular choice because (unlike all other distributions) otherwise this template would not publish its RealType argument and so users could not write generic code that accessed this second template parameter. In this respect, the choice is consistent with the other distributions in TR1.
We have two reasons for recommending that a real type be specified instead. One reason is based specifically on characteristics of binomial distribution implementations, while the other is based on mathematical characteristics of probability distribution functions in general.
Implementations of binomial distributions commonly use Stirling approximations for values in certain ranges. It is far more natural to use real values to represent these approximations than it would be to use integral values to do so. In other ranges, implementations reply on the Bernoulli distribution to obtain values. While TR1's bernoulli_distribution::input_type is specified as int, we believe this would be better specified as double.
This brings us to our main point: The notion of a random distribution rests on the notion of a cumulative distribution function, which in turn mathematically depends on a continuous dependent variable. Indeed, such a distribution function would be meaningless if it depended on discrete values such as integers - and this remains true even if the distribution function were to take discrete steps.
Although this note is specifically about binomial_distribution::input_type, we intend to recommend that all of the random distributions input_types be specified as a real type (either a RealType template parameter, or double, as appropriate).
Of the nine distributions in TR1, four already have this characteristic (uniform_real, exponential_distribution, normal_distribution, and gamma_distribution). We have already argued the case for the binomial the remaining four distributions.
In the case of uniform_int, we believe that the calculations to produce an integer result in a specified range from an integer in a different specified range is best done using real arithmetic. This is because it involves a product, one of whose terms is the ratio of the extents of the two ranges. Without real arithmetic, the results become less uniform: some numbers become more (or less) probable that they should be. This is, of course, undesireable behavior in a uniform distribution.
Finally, we believe that in the case of the bernoulli_distribution (briefly mentioned earlier), as well as the cases of the geometric_distribution and the poisson_distribution, it would be far more natural to have a real input_type. This is because the most natural computation involves the random number delivered and the distribution's parameter p (in the case of bernoulli_distribution, for example, the computation is a comparison against p), and p is already specified in each case as having some real type.
Proposed resolution:
typedef RealType input_type;
[ Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been eliminated. ]
Section: 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand.eng].
View all issues with NAD Editorial status.
Discussion:
Paragraph 8 specifies the algorithm by which a subtract_with_carry_01 engine is to be seeded given a single unsigned long. This algorithm is seriously flawed in the case where the engine parameter w (also known as word_size) exceeds 31 [bits]. The key part of the paragraph reads:
sets x(-r) ... x(-1) to (lcg(1)*2**(-w)) mod 1
and so forth.
Since the specified linear congruential engine, lcg, delivers numbers with a maximum of 2147483563 (just a shade under 31 bits), then when w is, for example, 48, each of the x(i) will be less than 2**-17. The consequence is that roughly the first 400 numbers delivered will be conspicuously close to either zero or one.
Unfortunately, this is not an innocuous flaw: One of the predefined engines in [tr.rand.predef], namely ranlux64_base_01, has w = 48 and would exhibit this poor behavior, while the original N1378 proposal states that these pre-defined engines are intended to be of "known good properties."
Proposed resolution:
In 5.1.4.4 [tr.rand.eng.sub1], replace the "effects" clause for void seed(unsigned long value = 19780503) by
Effects: If value == 0, sets value to 19780503. In any case,
with a linear congruential generator lcg(i) having parameters mlcg = 2147483563, alcg = 40014, clcg = 0, and lcg(0) = value,sets carry(-1) and x(-r) … x(-1) as if executinglinear_congruential<unsigned long, 40014, 0, 2147483563> lcg(value); seed(lcg);
to (lcg(1) · 2-w) mod 1 … (lcg(r) · 2-w) mod 1, respectively. If x(-1) == 0, sets carry(-1) = 2-w, else sets carry(-1) = 0.
[ Jens provided revised wording post Mont Tremblant. ]
[ Berlin: N1932 adopts the originally-proposed resolution of the issue. Jens's supplied wording is a clearer description of what is intended. Moved to Ready. ]
Rationale:
Jens: I'm using an explicit type here, because fixing the prose would probably not qualify for the (with issue 504 even stricter) requirements we have for seed(Gen&).
[ Portland: Subsumed by N2111. ]
Section: 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand.eng].
View all issues with NAD Editorial status.
Discussion:
Paragraph 3 begins:
The size of the state is r.
However, this is not quite consistent with the remainder of the paragraph which specifies a total of nr+1 items in the textual representation of the state. We recommend the sentence be corrected to match:
The size of the state is nr+1.
To give meaning to the coefficient n, it may be also desirable to move n's definition from later in the paragraph. Either of the following seem reasonable formulations:
With n=..., the size of the state is nr+1.
The size of the state is nr+1, where n=... .
Proposed resolution:
[ Jens: I plead for "NAD" on the grounds that "size of state" is only used as an argument for big-O complexity notation, thus constant factors and additions don't count. ]
[ Berlin: N1932 adopts the proposed NAD. ]
Section: 26.5.3.3 [rand.eng.sub], TR1 5.1.4.3 [tr.rand.eng.sub] Status: NAD Editorial Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all issues with NAD Editorial status.
Discussion:
Paragraph 2 begins:
The size of the state is r.
However, the next sentence specifies a total of r+1 items in the textual representation of the state, r specific x's as well as a specific carry. This makes a total of r+1 items that constitute the size of the state, rather than r.
Proposed resolution:
We recommend the sentence be corrected to match:
The size of the state is r+1.
[ Jens: I plead for "NAD" on the grounds that "size of state" is only used as an argument for big-O complexity notation, thus constant factors and additions don't count. ]
[ Berlin: N1932 adopts the proposed NAD. ]
Section: 26.5.1 [rand.synopsis], TR1 5.1.2 [tr.rand.synopsis] Status: NAD Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand.synopsis].
View all issues with NAD status.
Discussion:
To accompany the concept of a pseudo-random number engine as defined in Table 17, we propose and recommend an adjunct template, engine_traits, to be declared in [tr.rand.synopsis] as:
template< class PSRE > class engine_traits;
This template's primary purpose would be as an aid to generic programming involving pseudo-random number engines. Given only the facilities described in tr1, it would be very difficult to produce any algorithms involving the notion of a generic engine. The intent of this proposal is to provide, via engine_traits<>, sufficient descriptive information to allow an algorithm to employ a pseudo-random number engine without regard to its exact type, i.e., as a template parameter.
For example, today it is not possible to write an efficient generic function that requires any specific number of random bits. More specifically, consider a cryptographic application that internally needs 256 bits of randomness per call:
template< class Eng, class InIter, class OutIter > void crypto( Eng& e, InIter in, OutIter out );
Without knowning the number of bits of randomness produced per call to a provided engine, the algorithm has no means of determining how many times to call the engine.
In a new section [tr.rand.eng.traits], we proposed to define the engine_traits template as:
template< class PSRE >
class engine_traits
{
static std::size_t bits_of_randomness = 0u;
static std::string name() { return "unknown_engine"; }
// TODO: other traits here
};
Further, each engine described in [tr.rand.engine] would be accompanied by a complete specialization of this new engine_traits template.
Proposed resolution:
[ Berlin: Walter: While useful for implementation per TR1, N1932 has no need for this feature. Recommend close as NAD. ]
Rationale:
Recommend NAD, N1932, N2111 covers this. Already in WP.
Section: 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] Status: NAD Editorial Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand.eng].
View all issues with NAD Editorial status.
Discussion:
Paragraph 6 says:
... obtained by successive invocations of g, ...
We recommend instead:
... obtained by taking successive invocations of g mod 2**32, ...
as the context seems to require only 32-bit quantities be used here.
Proposed resolution:
Berlin: N1932 adopts the proposed resultion: see 26.3.3.4/7. Moved to Ready.
[ Portland: Subsumed by N2111. ]
Section: X [rand.req], TR1 5.1.1 [tr.rand.req] Status: NAD Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-03-13
View all other issues in [rand.req].
View all issues with NAD status.
Discussion:
The last two rows of Table 16 deal with the i/o requirements of an engine, specifying that the textual representation of an engine's state, appropriately formatted, constitute the engine's external representation.
This seems adequate when an engine's type is known. However, it seems inadequate in the context of generic code, where it becomes useful and perhaps even necessary to determine an engine's type via input.
Proposed resolution:
We therefore recommend that, in each of these two rows of Table 16, the text "textual representation" be expanded so as to read "engine name followed by the textual representation."
[ Berlin: N1932 considers this NAD. This is a QOI issue. ]
Section: 28 [re] Status: NAD Future Submitter: Eric Niebler Opened: 2005-07-01 Last modified: 2009-07-15
View all other issues in [re].
View all issues with NAD Future status.
Discussion:
A problem with TR1 regex is currently being discussed on the Boost developers list. It involves the handling of case-insensitive matching of character ranges such as [Z-a]. The proper behavior (according to the ECMAScript standard) is unimplementable given the current specification of the TR1 regex_traits<> class template. John Maddock, the author of the TR1 regex proposal, agrees there is a problem. The full discussion can be found at http://lists.boost.org/boost/2005/06/28850.php (first message copied below). We don't have any recommendations as yet.
-- Begin original message --
The situation of interest is described in the ECMAScript specification (ECMA-262), section 15.10.2.15:
"Even if the pattern ignores case, the case of the two ends of a range is significant in determining which characters belong to the range. Thus, for example, the pattern /[E-F]/i matches only the letters E, F, e, and f, while the pattern /[E-f]/i matches all upper and lower-case ASCII letters as well as the symbols [, \, ], ^, _, and `."
A more interesting case is what should happen when doing a case-insentitive match on a range such as [Z-a]. It should match z, Z, a, A and the symbols [, \, ], ^, _, and `. This is not what happens with Boost.Regex (it throws an exception from the regex constructor).
The tough pill to swallow is that, given the specification in TR1, I don't think there is any effective way to handle this situation. According to the spec, case-insensitivity is handled with regex_traits<>::translate_nocase(CharT) -- two characters are equivalent if they compare equal after both are sent through the translate_nocase function. But I don't see any way of using this translation function to make character ranges case-insensitive. Consider the difficulty of detecting whether "z" is in the range [Z-a]. Applying the transformation to "z" has no effect (it is essentially std::tolower). And we're not allowed to apply the transformation to the ends of the range, because as ECMA-262 says, "the case of the two ends of a range is significant."
So AFAICT, TR1 regex is just broken, as is Boost.Regex. One possible fix is to redefine translate_nocase to return a string_type containing all the characters that should compare equal to the specified character. But this function is hard to implement for Unicode, and it doesn't play nice with the existing ctype facet. What a mess!
-- End original message --
[ John Maddock adds: ]
One small correction, I have since found that ICU's regex package does implement this correctly, using a similar mechanism to the current TR1.Regex.
Given an expression [c1-c2] that is compiled as case insensitive it:
Enumerates every character in the range c1 to c2 and converts it to it's case folded equivalent. That case folded character is then used a key to a table of equivalence classes, and each member of the class is added to the list of possible matches supported by the character-class. This second step isn't possible with our current traits class design, but isn't necessary if the input text is also converted to a case-folded equivalent on the fly.
ICU applies similar brute force mechanisms to character classes such as [[:lower:]] and [[:word:]], however these are at least cached, so the impact is less noticeable in this case.
Quick and dirty performance comparisons show that expressions such as "[X-\\x{fff0}]+" are indeed very slow to compile with ICU (about 200 times slower than a "normal" expression). For an application that uses a lot of regexes this could have a noticeable performance impact. ICU also has an advantage in that it knows the range of valid characters codes: code points outside that range are assumed not to require enumeration, as they can not be part of any equivalence class. I presume that if we want the TR1.Regex to work with arbitrarily large character sets enumeration really does become impractical.
Finally note that Unicode has:
Three cases (upper, lower and title). One to many, and many to one case transformations. Character that have context sensitive case translations - for example an uppercase sigma has two different lowercase forms - the form chosen depends on context(is it end of a word or not), a caseless match for an upper case sigma should match either of the lower case forms, which is why case folding is often approximated by tolower(toupper(c)).
Probably we need some way to enumerate character equivalence classes, including digraphs (either as a result or an input), and some way to tell whether the next character pair is a valid digraph in the current locale.
Hoping this doesn't make this even more complex that it was already,
[ Portland: Alisdair: Detect as invalid, throw an exception. Pete: Possible general problem with case insensitive ranges. ]
[ 2009-07 Frankfurt ]
We agree that this is a problem, but we do not know the answer.
We are going to declare this NAD until existing practice leads us in some direction.
No objection to NAD Future.
Move to NAD Future.
Proposed resolution:
Section: 20.6.4 [meta.unary], TR1 4.5 [tr.meta.unary] Status: NAD Editorial Submitter: Robert Klarer Opened: 2005-07-11 Last modified: 2008-03-13
View all issues with NAD Editorial status.
Discussion:
It is not completely clear how the primary type traits deal with cv-qualified types. And several of the secondary type traits seem to be lacking a definition.
[ Berlin: Howard to provide wording. ]
Proposed resolution:
Wording provided in N2028. A revision (N2157) provides more detail for motivation.
Rationale:
Solved by revision (N2157) in the WP.Section: 23.2.3 [sequence.reqmts] Status: NAD Submitter: Chris Jefferson Opened: 2005-09-14 Last modified: 2008-03-13
View all other issues in [sequence.reqmts].
View all issues with NAD status.
Discussion:
Problem: There are a number of places in the C++ standard library where it is possible to write what appear to be sensible ways of calling functions, but which can cause problems in some (or all) implementations, as they cause the values given to the function to be changed in a way not specified in standard (and therefore not coded to correctly work). These fall into two similar categories.
1) Parameters taken by const reference can be changed during execution of the function
Examples:
Given std::vector<int> v:
v.insert(v.begin(), v[2]);
v[2] can be changed by moving elements of vector
Given std::list<int> l:
l.remove(*l.begin());
Will delete the first element, and then continue trying to access it. This is particularily vicious, as it will appear to work in almost all cases.
2) A range is given which changes during the execution of the function: Similarly,
v.insert(v.begin(), v.begin()+4, v.begin()+6);
This kind of problem has been partly covered in some cases. For example std::copy(first, last, result) states that result cannot be in the range [first, last). However, does this cover the case where result is a reverse_iterator built from some iterator in the range [first, last)? Also, std::copy would still break if result was reverse_iterator(last + 1), yet this is not forbidden by the standard
Solution:
One option would be to try to more carefully limit the requirements of each function. There are many functions which would have to be checked. However as has been shown in the std::copy case, this may be difficult. A simpler, more global option would be to somewhere insert text similar to:
If the execution of any function would change either any values passed by reference or any value in any range passed to a function in a way not defined in the definition of that function, the result is undefined.
Such code would have to at least cover chapters 23 and 25 (the sections I read through carefully). I can see no harm on applying it to much of the rest of the standard.
Some existing parts of the standard could be improved to fit with this, for example the requires for 25.2.1 (Copy) could be adjusted to:
Requires: For each non-negative integer n < (last - first), assigning to *(result + n) must not alter any value in the range [first + n, last).
However, this may add excessive complication.
One other benefit of clearly introducing this text is that it would allow a number of small optimisations, such as caching values passed by const reference.
Matt Austern adds that this issue also exists for the insert and erase members of the ordered and unordered associative containers.
[ Berlin: Lots of controversey over how this should be solved. Lots of confusion as to whether we're talking about self referencing iterators or references. Needs a good survey as to the cases where this matters, for which implementations, and how expensive it is to fix each case. ]
Proposed resolution:
Rationale:
Recommend NAD.
Section: 23.5 [unord], TR1 6.3.4 [tr.unord.unord] Status: NAD Submitter: Paolo Carlini Opened: 2005-10-12 Last modified: 2008-03-13
View all other issues in [unord].
View all issues with NAD status.
Discussion:
while implementing the resolution of issue 6.19 I'm noticing the following: according to 6.3.4.3/2 (and 6.3.4.5/2), for unordered_set and unordered_multiset:
"The iterator and const_iterator types are both const types. It is unspecified whether they are the same type"
Now, according to the resolution of 6.19, we have overloads of insert with hint and erase (single and range) both for iterator and const_iterator, which, AFAICS, can be meaningful at the same time *only* if iterator and const_iterator *are* in fact different types.
Then, iterator and const_iterator are *required* to be different types? Or that is an unintended consequence? Maybe the overloads for plain iterators should be added only to unordered_map and unordered_multimap? Or, of course, I'm missing something?
Proposed resolution:
Add to 6.3.4.3p2 (and 6.3.4.5p2):
2 ... The iterator and const_iterator types are both const
constant iterator types.
It is unspecified whether they are the same type.
Add a new subsection to 17.4.4 [lib.conforming]:
An implementation shall not supply an overloaded function signature specified in any library clause if such a signature would be inherently ambiguous during overload resolution due to two library types referring to the same type.
[Note: For example, this occurs when a container's iterator and const_iterator types are the same. -- end note]
[ Post-Berlin: Beman supplied wording. ]
Rationale:
Toronto: The first issue has been fixed by N2350 (the insert and erase members are collapsed into one signature). Alisdair to open a separate issue on the chapter 17 wording.Section: 17.6.3.11 [res.on.required] Status: NAD Editorial Submitter: David Abrahams Opened: 2005-10-25 Last modified: 2008-03-13
View all issues with NAD Editorial status.
Discussion:
17.4.3.8/1 says:
Violation of the preconditions specified in a function's Required behavior: paragraph results in undefined behavior unless the function's Throws: paragraph specifies throwing an exception when the precondition is violated.
This implies that a precondition violation can lead to defined behavior. That conflicts with the only reasonable definition of precondition: that a violation leads to undefined behavior. Any other definition muddies the waters when it comes to analyzing program correctness, because precondition violations may be routinely done in correct code (e.g. you can use std::vector::at with the full expectation that you'll get an exception when your index is out of range, catch the exception, and continue). Not only is it a bad example to set, but it encourages needless complication and redundancy in the standard. For example:
21 Strings library 21.3.3 basic_string capacity void resize(size_type n, charT c); 5 Requires: n <= max_size() 6 Throws: length_error if n > max_size(). 7 Effects: Alters the length of the string designated by *this as follows:
The Requires clause is entirely redundant and can be dropped. We could make that simplifying change (and many others like it) even without changing 17.4.3.8/1; the wording there just seems to encourage the redundant and error-prone Requires: clause.
[ Batavia: Alan and Pete to work. ]
[ Bellevue: NAD Editorial, this group likes N2121, Pete agrees, accepting it is Pete's business. General agreement that precondition violations are synonymous with UB. ]
Proposed resolution:
1. Change 17.4.3.8/1 to read:
Violation of the preconditions specified in a function's Required behavior: paragraph results in undefined behavior
unless the function's Throws: paragraph specifies throwing an exception when the precondition is violated.
2. Go through and remove redundant Requires: clauses. Specifics to be provided by Dave A.
[ Berlin: The LWG requests a detailed survey of part 2 of the proposed resolution. ]
[ Alan provided the survey N2121. ]
Section: 23.2 [container.requirements] Status: Dup Submitter: Joaquín M López Muñoz Opened: 2005-12-17 Last modified: 2007-04-18
View other active issues in [container.requirements].
View all other issues in [container.requirements].
View all issues with Dup status.
Duplicate of: 589
Discussion:
The iterator constructor X(i,j) for containers as defined in 23.1.1 and 23.2.2 does only require that i and j be input iterators but nothing is said about their associated value_type. There are three sensible options:
The issue has practical implications, and stdlib vendors have taken divergent approaches to it: Dinkumware follows 2, libstdc++ follows 3.
The same problem applies to the definition of insert(p,i,j) for sequences and insert(i,j) for associative contianers, as well as assign.
[ The following added by Howard and the example code was originally written by Dietmar. ]
Valid code below?
#include <vector>
#include <iterator>
#include <iostream>
struct foo
{
explicit foo(int) {}
};
int main()
{
std::vector<int> v_int;
std::vector<foo> v_foo1(v_int.begin(), v_int.end());
std::vector<foo> v_foo2((std::istream_iterator<int>(std::cin)),
std::istream_iterator<int>());
}
[ Berlin: Some support, not universal, for respecting the explicit qualifier. ]
Proposed resolution:
Section: C.2 [diff.library] Status: NAD Editorial Submitter: Martin Sebor Opened: 2005-11-25 Last modified: 2007-04-24
View other active issues in [diff.library].
View all other issues in [diff.library].
View all issues with NAD Editorial status.
Discussion:
According to C.2.2.3, p1, "the macro NULL, defined in any of <clocale>, <cstddef>, <cstdio>, <cstdlib>, <cstring>, <ctime>, or <cwchar>." This is consistent with the C standard.
However, Table 95 in C.2 fails to mention <clocale> and <cstdlib>.
In addition, C.2, p2 claims that "The C++ Standard library provides 54 standard macros from the C library, as shown in Table 95." While table 95 does have 54 entries, since a couple of them (including the NULL macro) are listed more than once, the actual number of macros defined by the C++ Standard Library may not be 54.
Proposed resolution:
I propose we add <clocale> and <cstdlib> to Table 96 and remove the number of macros from C.2, p2 and reword the sentence as follows:
The C++ Standard library
provides 54 standard macros fromdefines a number macros corresponding to those defined by the C Standard library, as shown in Table 96.
[ Portland: Resolution is considered editorial. It will be incorporated into the WD. ]
Section: TR1 5.1.1 [tr.rand.req] Status: NAD Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2009-07-15
View all issues with NAD status.
Discussion:
The TR sneaks in two new integer types, _Longlong and _Ulonglong, in [tr.c99]. The rest of the TR should use that type. I believe this affects two places. First, the random number requirements, 5.1.1/10-11, lists all of the types with which template parameters named IntType and UIntType may be instantiated. _Longlong (or "long long", assuming it is added to C++0x) should be added to the IntType list, and UIntType (again, or "unsigned long long") should be added to the UIntType list. Second, 6.3.2 lists the types for which hash<> is required to be instantiable. _Longlong and _Ulonglong should be added to that list, so that people may use long long as a hash key.
[ 2009-07 Frankfurt ]
We are not going to fix TR1.
The paper "long long goes to the library" addresses the integration of long long into the C++0x library.
Move to NAD.
Proposed resolution:
Section: 26.5 [rand], TR1 5.1 [tr.rand] Status: NAD Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2007-04-18
View all other issues in [rand].
View all issues with NAD status.
Discussion:
Paragraph 10 describes how a variate generator uses numbers produced by an engine to pass to a generator. The sentence that concerns me is: "Otherwise, if the value for engine_value_type::result_type is true and the value for Distribution::input_type is false [i.e. if the engine produces integers and the engine wants floating-point values], then the numbers in s_eng are divided by engine().max() - engine().min() + 1 to obtain the numbers in s_e." Since the engine is producing integers, both the numerator and the denominator are integers and we'll be doing integer division, which I don't think is what we want. Shouldn't we be performing a conversion to a floating-point type first?
Proposed resolution:
Rationale:
Recommend NAD as the affected section is now gone and so the issue is moot. N2111.
Section: 26.5.6 [rand.device], TR1 5.1.6 [tr.rand.device] Status: NAD Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2007-10-18
View all other issues in [rand.device].
View all issues with NAD status.
Discussion:
Class random_device "produces non-deterministic random numbers", using some external source of entropy. In most real-world systems, the amount of available entropy is limited. Suppose that entropy has been exhausted. What is an implementation permitted to do? In particular, is it permitted to block indefinitely until more random bits are available, or is the implementation required to detect failure immediately? This is not an academic question. On Linux a straightforward implementation would read from /dev/random, and "When the entropy pool is empty, reads to /dev/random will block until additional environmental noise is gathered." Programmers need to know whether random_device is permitted to (or possibly even required to?) behave the same way.
[ Berlin: Walter: N1932 considers this NAD. Does the standard specify whether std::cin may block? ]
See N2391 and N2423 for some further discussion.
Proposed resolution:
Adopt the proposed resolution in N2423 (NAD).
Section: 26.5.8 [rand.dist], TR1 5.1.7.5 [tr.rand.dist.bin] Status: NAD Editorial Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2007-04-24
View all other issues in [rand.dist].
View all issues with NAD Editorial status.
Discussion:
Paragraph 1 says that "A binomial distributon random distribution produces integer values i>0 with p(i) = (n choose i) * p*i * (1-p)^(t-i), where t and p are the parameters of the distribution. OK, that tells us what t, p, and i are. What's n?
Proposed resolution:
Berlin: Typo: "n" replaced by "t" in N1932: see 26.3.7.2.2/1.
[ Portland: Subsumed by N2111. ]
Section: 18.4.1 [cstdint.syn], TR1 8.22.1 [tr.c99.cstdint.syn] Status: NAD Editorial Submitter: Paolo Carlini Opened: 2006-01-30 Last modified: 2007-07-02
View all other issues in [cstdint.syn].
View all issues with NAD Editorial status.
Discussion:
In the synopsis, some types are identified as optional: int8_t, int16_t, and so on, consistently with C99, indeed.
On the other hand, intptr_t and uintptr_t, are not marked as such and probably should, consistently with C99, 7.18.1.4.
Proposed resolution:
Change 18.4.1 [cstdint.syn]:
... typedef signed integer type intptr_t; // optional ... typedef unsigned integer type uintptr_t; // optional ...
Rationale:
Recommend NAD and fix as editorial with the proposed resolution.Section: 18.3.1.5 [numeric.special] Status: NAD Submitter: Howard Hinnant Opened: 2006-01-29 Last modified: 2007-01-15
View all other issues in [numeric.special].
View all issues with NAD status.
Discussion:
I believe we have a bug in the resolution of: lwg 184 (WP status).
The resolution spells out each member of numeric_limits<bool>. The part I'm having a little trouble with is:
static const bool traps = false;
Should this not be implementation defined? Given:
int main()
{
bool b1 = true;
bool b2 = false;
bool b3 = b1/b2;
}
If this causes a trap, shouldn't numeric_limits<bool>::traps be true?
Proposed resolution:
Change 18.2.1.5p3:
-3- The specialization for bool shall be provided as follows:
namespace std { template <> class numeric_limits<bool> { ... static const bool traps =falseimplementation-defined; ... }; }
[ Redmond: NAD because traps refers to values, not operations. There is no bool value that will trap. ]
Section: TR1 8.21 [tr.c99.boolh] Status: NAD Editorial Submitter: Paolo Carlini Opened: 2006-02-02 Last modified: 2007-04-24
View all issues with NAD Editorial status.
Discussion:
This one, if nobody noticed it yet, seems really editorial: s/cstbool/cstdbool/
Proposed resolution:
Change 8.21p1:
-1- The header behaves as if it defines the additional macro defined in <cstdbool> by including the header <cstdbool>.
[ Redmond: Editorial. ]
Section: 18.4 [cstdint], TR1 8.22 [tr.c99.cstdint] Status: NAD Editorial Submitter: Paolo Carlini Opened: 2006-02-06 Last modified: 2008-07-02
View all other issues in [cstdint].
View all issues with NAD Editorial status.
Discussion:
I'm seeing a problem with such overloads: when, _Longlong == intmax_t == long long we end up, essentially, with the same arguments and different return types (lldiv_t and imaxdiv_t, respectively). Similar issue with abs(_Longlong) and abs(intmax_t), of course.
Comparing sections 8.25 and 8.11, I see an important difference, however: 8.25.3 and 8.25.4 carefully describe div and abs for _Longlong types (rightfully, because not moved over directly from C99), whereas there is no equivalent in 8.11: the abs and div overloads for intmax_t types appear only in the synopsis and are not described anywhere, in particular no mention in 8.11.2 (at variance with 8.25.2).
I'm wondering whether we really, really, want div and abs for intmax_t...
Proposed resolution:
[ Portland: no consensus. ]
Rationale:
[ Batavia, Bill: The <cstdint> synopsis in TR1 8.11.1 [tr.c99.cinttypes.syn] contains: ]
intmax_t imaxabs(intmax_t i); intmax_t abs(intmax_t i); imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); imaxdiv_t div(intmax_t numer, intmax_t denom);
[ and in TR1 8.11.2 [tr.c99.cinttypes.def]: ]
The header defines all functions, types, and macros the same as C99 subclause 7.8.
[ This is as much definition as we give for most other C99 functions, so nothing need change. We might, however, choose to add the footnote: ]
[Note: These overloads for abs and div may well be equivalent to those that take long long arguments. If so, the implementation is responsible for avoiding conflicting declarations. -- end note]
[ Bellevue: NAD Editorial. Pete must add a footnote, as described below. ]
[ Looks like a real problem. Dietmar suggests div() return a template type. Matt: looks like imaxdiv_t is loosly defined. Can it be a typedef for lldiv_t when _Longlong == intmax_t? PJP seems to agree. We would need a non-normative note declaring that the types lldiv_t and imaxdiv_t may not be unique if intmax_t==_longlong. ]
Section: 24.2.1 [input.iterators] Status: NAD Editorial Submitter: David Abrahams Opened: 2006-02-09 Last modified: 2007-04-24
View all other issues in [input.iterators].
View all issues with NAD Editorial status.
Discussion:
24.1.1 Input iterators [lib.input.iterators]
1 A class or a built-in type X satisfies the requirements of an input iterator for the value type T if the following expressions are valid, where U is the type of any specified member of type T, as shown in Table 73.
There is no capital U used in table 73. There is a lowercase u, but that is clearly not meant to denote a member of type T. Also, there's no description in 24.1.1 of what lowercase a means. IMO the above should have been...Hah, a and b are already covered in 24.1/11, so maybe it should have just been:
Proposed resolution:
Change 24.1.1p1:
-1- A class or a built-in type X satisfies the requirements of an input iterator for the value type T if the following expressions are valid
, where U is the type of any specified member of type T,as shown in Table 73.
[ Portland: Editorial. ]
Section: 20.2.2 [allocator.requirements] Status: NAD Submitter: Sergey P. Derevyago Opened: 2006-02-17 Last modified: 2007-04-18
View other active issues in [allocator.requirements].
View all other issues in [allocator.requirements].
View all issues with NAD status.
Discussion:
User-defined allocators without default constructor are not explicitly supported by the standard but they can be supported just like std::vector supports elements without default constructor.
As a result, there exist implementations that work well with such allocators and implementations that don't.
1) The standard doesn't explicitly state this intent but it should. In particular, 20.1.5p5 explicitly state the intent w.r.t. the allocator instances that compare non-equal. So it can similarly state the intent w.r.t. the user-defined allocators without default constructor.
2) Some container operations are obviously underspecified. In particular, 21.3.7.1p2 tells:
template<class charT, class traits, class Allocator> basic_string<charT,traits,Allocator> operator+( const charT* lhs, const basic_string<charT,traits,Allocator>& rhs );Returns: basic_string<charT,traits,Allocator>(lhs) + rhs.
That leads to the basic_string<charT,traits,Allocator>(lhs, Allocator()) call. Obviously, the right requirement is:
Returns: basic_string<charT,traits,Allocator>(lhs, rhs.get_allocator()) + rhs.
It seems like a lot of DRs can be submitted on this "Absent call to get_allocator()" topic.
1) Explicitly state the intent to allow for user-defined allocators without default constructor in 20.1.5 Allocator requirements.
2) Correct all the places, where a correct allocator object is available through the get_allocator() call but default Allocator() gets passed instead.
Let's suppose that the following memory pool is available:
class mem_pool {
// ...
void* allocate(size_t size);
void deallocate(void* ptr, size_t size);
};
So the following allocator can be implemented via this pool:
class stl_allocator {
mem_pool& pool;
public:
explicit stl_allocator(mem_pool& mp) : pool(mp) {}
stl_allocator(const stl_allocator& sa) : pool(sa.pool) {}
template <class U>
stl_allocator(const stl_allocator<U>& sa) : pool(sa.get_pool()) {}
~stl_allocator() {}
pointer allocate(size_type n, std::allocator<void>::const_pointer = 0)
{
return (n!=0) ? static_cast<pointer>(pool.allocate(n*sizeof(T))) : 0;
}
void deallocate(pointer p, size_type n)
{
if (n!=0) pool.deallocate(p, n*sizeof(T));
}
// ...
};
Then the following code works well on some implementations and doesn't work on another:
typedef basic_string<char, char_traits<char>, stl_allocator<char> >
tl_string;
mem_pool mp;
tl_string s1("abc", stl_allocator<int>(mp));
printf("(%s)\n", ("def"+s1).c_str());
In particular, on some implementations the code can't be compiled without default stl_allocator() constructor.
The obvious way to solve the compile-time problems is to intentionally define a NULL pointer dereferencing default constructor
stl_allocator() : pool(*static_cast<mem_pool*>(0)) {}
in a hope that it will not be called. The problem is that it really gets called by operator+(const char*, const string&) under the current 21.3.7.1p2 wording.
Proposed resolution:
Rationale:
Recommend NAD. operator+() with string already requires the desired semantics of copying the allocator from one of the strings (lhs when there is a choice).
Section: TR1 8.16.4 [tr.c99.cmath.over] Status: NAD Submitter: Paolo Carlini Opened: 2006-03-07 Last modified: 2009-07-13
View all issues with NAD status.
Discussion:
log2 is missing from the list of "additional overloads" in TR1 8.16.4 [tr.c99.cmath.over] p1.
Hinnant: This is a TR1 issue only. It is fixed in the current (N2135) WD.
[ Batavia (2009-05): ]
We agree this has been fixed in the Working Draft. Move to NAD.
Proposed resolution:
Add log2 to the list of functions in TR1 8.16.4 [tr.c99.cmath.over] p1.
Section: 27.5.4.3 [iostate.flags] Status: Dup Submitter: Seungbeom Kim Opened: 2006-03-10 Last modified: 2006-12-30
View all other issues in [iostate.flags].
View all issues with Dup status.
Duplicate of: 272
Discussion:
Section: 27.4.4.3 [lib.iostate.flags]
Paragraph 4 says:
void clear(iostate state = goodbit);Postcondition: If rdbuf()!=0 then state == rdstate(); otherwise rdstate()==state|ios_base::badbit.
The postcondition "rdstate()==state|ios_base::badbit" is parsed as "(rdstate()==state)|ios_base::badbit", which is probably what the committee meant.
Rationale:
Section: 21.2 [char.traits] Status: NAD Submitter: Jack Reeves Opened: 2006-04-06 Last modified: 2008-06-18
View all other issues in [char.traits].
View all issues with NAD status.
Discussion:
Currently, the Standard Library specifies only a declaration for template class char_traits<> and requires the implementation provide two explicit specializations: char_traits<char> and char_traits<wchar_t>. I feel the Standard should require explicit specializations for all built-in character types, i.e. char, wchar_t, unsigned char, and signed char.
I have put together a paper (N1985) that describes this in more detail and includes all the necessary wording.
[ Portland: Jack will rewrite N1985 to propose a primary template that will work with other integral types. ]
[ Toronto: issue has grown with addition of char16_t and char32_t. ]
[ post Bellevue: ]
We suggest that Jack be asked about the status of his paper, and if it is not forthcoming, the work-item be assigned to someone else. If no one steps forward to do the paper before the next meeting, we propose to make this NAD without further discussion. We leave this Open for now, but our recommendation is NAD.
Note: the issue statement should be updated, as the Toronto comment has already been resolved. E.g., char_traits specializations for char16_t and char32_t are now in the working paper.
[ Sophia Antipolis: ]
Nobody has submitted the requested paper, so we move to NAD, as suggested by the decision at the last meeting.
Proposed resolution:
Section: 1.2 [intro.refs] Status: NAD Editorial Submitter: Beman Dawes Opened: 2006-04-08 Last modified: 2007-07-02
View all other issues in [intro.refs].
View all issues with NAD Editorial status.
Discussion:
1.2 Normative references [intro.refs] of the WP currently refers to ISO/IEC 9899:1990, Programming languages - C. Should that be changed to ISO/IEC 9899:1999?
What impact does this have on the library?
Proposed resolution:
In 1.2/1 [intro.refs] of the WP, change:
- ISO/IEC 9899:
19901999 + TC1 + TC2, Programming languages - C
Rationale:
Recommend NAD, fixed editorially.Section: 26.5 [rand], TR1 5.1 [tr.rand] Status: NAD Submitter: Howard Hinnant Opened: 2006-04-11 Last modified: 2007-04-18
View all other issues in [rand].
View all issues with NAD status.
Discussion:
In Berlin, as a working group, we voted in favor of N1932 which makes issue 507 moot: variate_generator has been eliminated. Then in full committee we voted to give this issue WP status (mistakenly).
Proposed resolution:
Strike the proposed resolution of issue 507.
[ post-Portland: Walter and Howard recommend NAD. The proposed resolution of 507 no longer exists in the current WD. ]
Rationale:
NAD. Will be moot once N2135 is adopted.
Section: 27.5.3 [fpos] Status: NAD Submitter: Beman Dawes Opened: 2006-04-12 Last modified: 2009-07-15
View all other issues in [fpos].
View all issues with NAD status.
Discussion:
There are two deficiencies related to file sizes:
The Dinkumware implementation of the Standard Library as shipped with the Microsoft compiler copes with these issues by:
fpos_t seekpos() const;
Because there are so many types relating to file positions and offsets (fpos_t, fpos, pos_type, off_type, streamoff, streamsize, streampos, wstreampos, and perhaps more), it is difficult to know if the Dinkumware extensions are sufficient. But they seem a useful starting place for discussions, and they do represent existing practice.
[ Kona (2007): We need a paper. It would be nice if someone proposed clarifications to the definitions of pos_type and off_type. Currently these definitions are horrible. Proposed Disposition: Open ]
[ 2009-07 Frankfurt ]
This is the subject of paper N2926.
If we choose to take any action, we will move the paper, so the issue can be closed.
Move to NAD.
Proposed resolution:
Section: 23.2.5 [unord.req] Status: NAD Submitter: Joaquín M López Muñoz Opened: 2006-06-13 Last modified: 2008-03-12
View other active issues in [unord.req].
View all other issues in [unord.req].
View all issues with NAD status.
Discussion:
See N2023 for full discussion.
Proposed resolution:
Option 1:
The problem can be eliminated by omitting the requirement that a.erase(q) return an iterator. This is, however, in contrast with the equivalent requirements for other standard containers.
Option 2:
a.erase(q) can be made to compute the next iterator only when explicitly requested: the technique consists in returning a proxy object implicitly convertible to iterator, so that
iterator q1=a.erase(q);
works as expected, while
a.erase(q);
does not ever invoke the conversion-to-iterator operator, thus avoiding the associated computation. To allow this technique, some sections of TR1 along the line "return value is an iterator..." should be changed to "return value is an unspecified object implicitly convertible to an iterator..." Although this trick is expected to work transparently, it can have some collateral effects when the expression a.erase(q) is used inside generic code.
Rationale:
N2023 was discussed in Portland and the consensus was that there appears to be no need for either change proposed in the paper. The consensus opinion was that since the iterator could serve as its own proxy, there appears to be no need for the change. In general, "converts to" is undesirable because it interferes with template matching.
Post Toronto: There does not at this time appear to be consensus with the Portland consensus.
[ Bellevue: ]
The Bellevue review of this issue reached consensus with the Portland consensus, in contravention of the Toronto non-consensus. Common implementations have the iterator readily available, and most common uses depend on the iterator being returned.
Section: 20.8.10.1 [uninitialized.copy] Status: NAD Submitter: Martin Sebor Opened: 2006-06-14 Last modified: 2009-07-15
View all other issues in [uninitialized.copy].
View all issues with NAD status.
Discussion:
Related to 1029
The specialized algorithms [lib.specialized.algorithms] are specified as having the general effect of invoking the following expression:
new (static_cast<void*>(&*i))
typename iterator_traits<ForwardIterator>::value_type (x)
This expression is ill-formed when the type of the subexpression
&*i is some volatile-qualified T.
[ Batavia: Lack of support for proposed resolution but agree there is a defect. Howard to look at wording. Concern that move semantics properly expressed if iterator returns rvalue. ]
[ 2009-06-17 Pablo adds: ]
Propose that Issue 582 be closed NAD.
Issue 582 asks that uninitialized_copy, uninitialized_fill, and uninitialized_fill_n should be well-formed if the result type is volatile. My feeling is that the standard does not, and should not, guarantee any useful behavior when constructors are invoked on volatile storage, so making it syntactically legal to call uninitialized_copy on volatile storage is not useful. A possible editorial change would be to put my previous sentence into a non-normative note.
Note that the three sections starting with 20.8.10.1 [uninitialized.copy] do not yet have concepts. Here's a first crack at the first one:
template <InputIterator InIter, OutputIterator OutIter> requires ExplicitConvertible<HasDereference<OutIter::reference>::result, OutIter::value_type&> && Convertible<OutIter::value_type*, void*> && ExplicitConvertible<OutIter::value_type, InIter::reference> OutIter uninitialized_copy(InIter first, InIter last, OutIter result);Effects:
while (first != last) { typedef OutIter::value_type value_type; value_type& outRef = static_cast<value_type&>(*result++); ::new (static_cast<void*>(addressof(outRef))) value_type(*first++); }Notes:
- This definition is actually LESS constrained than in C++03 because there is no requirement that the result be a forward iterator.
- If OutIter returns a proxy type with an overloaded operator&, this definition probably won't compile. Lifting this limitation while allowing value_type to have an overloaded operator& would be hard, but is probably possible with careful overloading. I'm not sure it's worth it.
- This definition retains the prohibition on the use of volatile types for the result.
[ 2009-07 Frankfurt ]
We don't deal with volatile in the library.
Jim: should we state that explicitly somewhere?
Beman: you might argue that clause 17 should say something about volatile. However, if you want to raise we argument, we should open it as a separate issue and consult with experts on concurrency.
Hinnant: actually, some library components do handle volatile, so we'd need to be very careful about what we say in clause 17.
No objection to NAD.
Move to NAD.
Proposed resolution:
In order to allow these algorithms to operate on volatile storage I propose to change the expression so as to make it well-formed even for pointers to volatile types. Specifically, I propose the following changes to clauses 20 and 24. Change 20.6.4.1, p1 to read:
Effects:
typedef typename iterator_traits<ForwardIterator>::pointer pointer;
typedef typename iterator_traits<ForwardIterator>::value_type value_type;
for (; first != last; ++result, ++first)
new (static_cast<void*>(const_cast<pointer>(&*result))
value_type (*first);
change 20.6.4.2, p1 to read
Effects:
typedef typename iterator_traits<ForwardIterator>::pointer pointer;
typedef typename iterator_traits<ForwardIterator>::value_type value_type;
for (; first != last; ++result, ++first)
new (static_cast<void*>(const_cast<pointer>(&*first))
value_type (*x);
and change 20.6.4.3, p1 to read
Effects:
typedef typename iterator_traits<ForwardIterator>::pointer pointer;
typedef typename iterator_traits<ForwardIterator>::value_type value_type;
for (; n--; ++first)
new (static_cast<void*>(const_cast<pointer>(&*first))
value_type (*x);
In addition, since there is no partial specialization for
iterator_traits<volatile T*> I propose to add one
to parallel such specialization for <const T*>. Specifically, I
propose to add the following text to the end of 24.3.1, p3:
and for pointers to volatile as
namespace std {
template<class T> struct iterator_traits<volatile T*> {
typedef ptrdiff_t difference_type;
typedef T value_type;
typedef volatile T* pointer;
typedef volatile T& reference;
typedef random_access_iterator_tag iterator_category;
};
}
Note that the change to iterator_traits isn't necessary
in order to implement the specialized algorithms in a way that allows
them to operate on volatile strorage. It is only necesassary in order
to specify their effects in terms of iterator_traits as
is done here. Implementations can (and some do) achieve the same
effect by means of function template overloading.
Section: 26.8 [c.math] Status: NAD Submitter: Beman Dawes Opened: 2006-06-15 Last modified: 2007-07-25
View all other issues in [c.math].
View all issues with NAD status.
Discussion:
There is no div() function for unsigned integer types.
There are several possible resolutions. The simplest one is noted below. Other possibilities include a templated solution.
Proposed resolution:
Add to 26.7 [lib.c.math] paragraph 8:
struct udiv_t div(unsigned, unsigned); struct uldiv_t div(unsigned long, unsigned long); struct ulldiv_t div(unsigned long long, unsigned long long);
Rationale:
Toronto: C99 does not have these unsigned versions because the signed version exist just to define the implementation-defined behavior of signed integer division. Unsigned integer division has no implementation-defined behavior and thus does not need this treatment.Section: 26.8 [c.math] Status: NAD Submitter: Beman Dawes Opened: 2006-06-15 Last modified: 2007-07-25
View all other issues in [c.math].
View all issues with NAD status.
Discussion:
There is no pow() function for any integral type.
Proposed resolution:
Add something like:
template< typename T> T power( T x, int n ); // requires: n >=0
Rationale:
Toronto: We already have double pow(integral, integral) from 26.8 [c.math] p11.Section: 22.4 [locale.categories] Status: NAD Submitter: Martin Sebor, Paolo Carlini Opened: 2006-06-22 Last modified: 2009-07-15
View all other issues in [locale.categories].
View all issues with NAD status.
Discussion:
Section 22.2, paragraph 2 requires facet get() members
that take an ios_base::iostate& argument,
err, to ignore the (initial) value of the
argument, but to set it to ios_base::failbit in case of a
parse error.
We believe there are a few minor problems with this blanket
requirement in conjunction with the wording specific to each
get() member function.
First, besides get() there are other member functions
with a slightly different name (for example,
get_date()). It's not completely clear that the intent of
the paragraph is to include those as well, and at least one
implementation has interpreted the requirement literally.
Second, the requirement to "set the argument to
ios_base::failbit suggests that the functions are not
permitted to set it to any other value (such as
ios_base::eofbit, or even ios_base::eofbit |
ios_base::failbit).
However, 22.2.2.1.2, p5 (Stage 3 of num_get parsing) and
p6 (bool parsing) specifies that the do_get
functions perform err |= ios_base::eofbit, which
contradicts the earlier requirement to ignore err's initial
value.
22.2.6.1.2, p1 (the Effects clause of the money_get
facet's do_get member functions) also specifies that
err's initial value be used to compute the final
value by ORing it with either ios_base::failbit or
withios_base::eofbit | ios_base::failbit.
[ 2009-07 Frankfurt ]
Move to NAD.
Proposed resolution:
We believe the intent is for all facet member functions that take an
ios_base::iostate& argument to:
err argument,
err to ios_base::goodbit prior
to any further processing,
ios_base::eofbit, or
ios_base::failbit, or both in err, as
appropriate, in response to reaching the end-of-file or on parse
error, or both.
To that effect we propose to change 22.2, p2 as follows:
The put() members make no provision for error
reporting. (Any failures of the OutputIterator argument must be
extracted from the returned iterator.) Unless otherwise
specified, the get() members that
take an ios_base::iostate& argument whose value
they ignore, but set to ios_base::failbit in case of a parse
error., err, start by evaluating
err = ios_base::goodbit, and may subsequently set
err to either ios_base::eofbit, or
ios_base::failbit, or ios_base::eofbit |
ios_base::failbit in response to reaching the end-of-file or in
case of a parse error, or both, respectively.
[ Kona (2007): We need to change the proposed wording to clarify that the phrase "the get members" actually denotes get(), get_date(), etc. Proposed Disposition: Open ]
Section: D.7.2.1 [depr.istrstream.cons] Status: NAD Editorial Submitter: Martin Sebor Opened: 2006-06-22 Last modified: 2007-05-11
View all issues with NAD Editorial status.
Discussion:
The iststream(char*, streamsize) ctor is in the class
synopsis in D.7.2 but its signature is missing in the description
below (in D.7.2.1).
Proposed resolution:
This seems like a simple editorial issue and the missing signature can
be added to the one for const char* in paragraph 2.
[ post Oxford: Noted that it is already fixed in N2284 ]
Section: 20.6 [meta], TR1 4.9 [tr.meta.req] Status: NAD Editorial Submitter: Beman Dawes Opened: 2006-08-10 Last modified: 2007-05-11
View other active issues in [meta].
View all other issues in [meta].
View all issues with NAD Editorial status.
Discussion:
20.4.9 [lib.meta.req], Implementation requirements, provides latitude for type traits implementers that is not needed in C++0x. It includes the wording:
[Note: the latitude granted to implementers in this clause is temporary, and is expected to be removed in future revisions of this document. -- end note]
Note: N2157: Minor Modifications to the type traits Wording also has the intent of removing this wording from the WP.
Proposed resolution:
Remove 20.4.9 [lib.meta.req] in its entirety from the WP.
[ post-Oxford: Recommend NAD Editorial. This resolution is now in the current working draft. ]
Section: 18.3.1.2 [numeric.limits.members] Status: NAD Editorial Submitter: whyglinux Opened: 2006-08-08 Last modified: 2007-07-02
View all other issues in [numeric.limits.members].
View all issues with NAD Editorial status.
Discussion:
18.2.1.2 numeric_limits members [lib.numeric.limits.members] Paragraph 7:
"For built-in integer types, the number of non-sign bits in the representation."
26.1 Numeric type requirements [lib.numeric.requirements] Footnote:
"In other words, value types. These include built-in arithmetic types, pointers, the library class complex, and instantiations of valarray for value types."
Integer types (which are bool, char, wchar_t, and the signed and unsigned integer types) and arithmetic types (which are integer and floating types) are all built-in types and thus there are no non-built-in (that is, user-defined) integer or arithmetic types. Since the redundant "built-in" in the above 2 sentences can mislead that there may be built-in or user-defined integer and arithmetic types (which is not correct), the "built-in" should be removed.
Proposed resolution:
18.2.1.2 numeric_limits members [lib.numeric.limits.members] Paragraph 7:
"For
built-ininteger types, the number of non-sign bits in the representation."
26.1 Numeric type requirements [lib.numeric.requirements] Footnote:
"In other words, value types. These include
built-inarithmetic types, pointers, the library class complex, and instantiations of valarray for value types."
Rationale:
Recommend NAD / Editorial. The proposed resolution is accepted as editorial.
Section: 27.9.1.9 [ifstream.members] Status: NAD Editorial Submitter: Christopher Kohlhoff Opened: 2006-08-17 Last modified: 2008-07-02
View all other issues in [ifstream.members].
View all issues with NAD Editorial status.
Discussion:
I just spotted a minor problem in 27.8.1.7 [lib.ifstream.members] para 4 and also 27.8.1.13 [lib.fstream.members] para 4. In both places it says:
void close();Effects: Calls rdbuf()->close() and, if that function returns false, ...
However, basic_filebuf::close() (27.8.1.2) returns a pointer to the filebuf on success, null on failure, so I think it is meant to say "if that function returns a null pointer". Oddly, it is correct for basic_ofstream.
Proposed resolution:
Change 27.9.1.9 [ifstream.members], p5:
Effects: Calls rdbuf()->close() and, if that function fails (returns
falsea null pointer), calls setstate(failbit) (which may throw ios_base::failure (27.4.4.3)).
Change 27.9.1.17 [fstream.members], p5:
Effects: Calls rdbuf()->close() and, if that function fails (returns
falsea null pointer), calls setstate(failbit) (which may throw ios_base::failure (27.4.4.3)).
[ Kona (2007): Proposed Disposition: NAD, Editorial ]
Section: TRDecimal 3.2 [trdec.types.types] Status: NAD Submitter: Daveed Vandevoorde Opened: 2006-04-05 Last modified: 2009-07-15
View all other issues in [trdec.types.types].
View all issues with NAD status.
Discussion:
In a private email, Daveed writes:
I am not familiar with the C TR, but my guess is that the class type approach still won't match a built-in type approach because the notion of "promotion" cannot be emulated by user-defined types.
Here is an example:
struct S {
S(_Decimal32 const&); // Converting constructor
};
void f(S);
void f(_Decimal64);
void g(_Decimal32 d) {
f(d);
}
If _Decimal32 is a built-in type, the call f(d) will likely resolve to f(_Decimal64) because that requires only a promotion, whereas f(S) requires a user-defined conversion.
If _Decimal32 is a class type, I think the call f(d) will be ambiguous because both the conversion to _Decimal64 and the conversion to S will be user-defined conversions with neither better than the other.
Robert comments:
In general, a library of arithmetic types cannot exactly emulate the behavior of the intrinsic numeric types. There are several ways to tell whether an implementation of the decimal types uses compiler intrinisics or a library. For example:
_Decimal32 d1;
d1.operator+=(5); // If d1 is a builtin type, this won't compile.
In preparing the decimal TR, we have three options:
We decided as a group to pursue option #3, but that approach implies that implementations may not agree on the semantics of certain use cases (first example, above), or on whether certain other cases are well-formed (second example). Another potentially important problem is that, under the present definition of POD, the decimal classes are not POD types, but builtins will be.
Note that neither example above implies any problems with respect to C-to-C++ compatibility, since neither example can be expressed in C.
[ 2009-07 Frankfurt ]
Decimal numeric types may either be builtin types or library types. We only intend to specify the common subset of behaviors of the two implementation approaches. The front matter of the Decimal TR says this explicitly.
Move to NAD.
Proposed resolution:
Section: TRDecimal 3.2 [trdec.types.types] Status: NAD Submitter: Martin Sebor Opened: 2006-06-15 Last modified: 2009-07-15
View all other issues in [trdec.types.types].
View all issues with NAD status.
Discussion:
In c++std-lib-17205, Martin writes:
...was it a deliberate design choice to make narrowing assignments ill-formed while permitting narrowing compound assignments? For instance:
decimal32 d32;
decimal64 d64;
d32 = 64; // error
d32 += 64; // okay
In c++std-lib-17229, Robert responds:
It is a vestige of an old idea that I forgot to remove from the paper. Narrowing assignments should be permitted. The bug is that the converting constructors that cause narrowing should not be explicit. Thanks for pointing this out.
[ 2009-07 Frankfurt ]
The current state of the Decimal TR is the result of a deliberate design decision that has been examined many times.
Move to NAD.
Proposed resolution:
1. In "3.2.2 Class decimal32" synopsis, remove the explicit specifier from the narrowing conversions:
// 3.2.2.2 conversion from floating-point type:
explicit decimal32(decimal64 d64);
explicit decimal32(decimal128 d128);
2. Do the same thing in "3.2.2.2. Conversion from floating-point type."
3. In "3.2.3 Class decimal64" synopsis, remove the explicit specifier from the narrowing conversion:
// 3.2.3.2 conversion from floating-point type:
explicit decimal64(decimal128 d128);
4. Do the same thing in "3.2.3.2. Conversion from floating-point type."
[ Redmond: We prefer explicit conversions for narrowing and implicit for widening. ]
Section: 21.4 [basic.string] Status: NAD Submitter: Bo Persson Opened: 2006-12-05 Last modified: 2009-07-15
View all other issues in [basic.string].
View all issues with NAD status.
Discussion:
This is based on N2134, where 21.3.1/2 states: "... The Allocator object used shall be a copy of the Allocator object passed to the basic_string object's constructor or, if the constructor does not take an Allocator argument, a copy of a default-constructed Allocator object."
Section 21.3.2/1 lists two constructors:
basic_string(const basic_string<charT,traits,Allocator>& str );
basic_string(const basic_string<charT,traits,Allocator>& str ,
size_type pos , size_type n = npos,
const Allocator& a = Allocator());
and then says "In the first form, the Allocator value used is copied from str.get_allocator().", which isn't an option according to 21.3.1.
[ Batavia: We need blanket statement to the effect of: ]
[ Review constructors and functions that return a string; make sure we follow these rules (substr, operator+, etc.). Howard to supply wording. ]
[
Bo adds: The new container constructor which takes only a size_type is not
consistent with 23.2 [container.requirements], p9 which says in part:
All other constructors for these container types take an
Allocator& argument (20.1.2), an allocator whose value type
is the same as the container's value type. A copy of this argument is
used for any memory allocation performed, by these constructors and by
all member functions, during the lifetime of each container object.
]
[ post Bellevue: We re-confirm that the issue is real. Pablo will provide wording. ]
[ 2009-07 Frankfurt ]
Move to NAD.
Proposed resolution:
Section: 21.6 [c.strings] Status: NAD Editorial Submitter: Bo Persson Opened: 2006-12-11 Last modified: 2007-04-24
View all other issues in [c.strings].
View all issues with NAD Editorial status.
Discussion:
In the current draft N2134, 21.4/1 says
"Tables 59,228) 60, 61, 62,and 63 229) 230) describe headers <cctype>, <cwctype>, <cstring>, <cwchar>, and <cstdlib> (character conversions), respectively."
Here footnote 229 applies to table 62, not table 63.
Also, footnote 230 lists the new functions in table 63, "atoll, strtoll, strtoull, strtof, and strtold added by TR1". However, strtof is not present in table 63.
Proposed resolution:
Rationale:
Recommend NAD, editorial. Send to Pete.
Section: 17.5.1.4 [structure.specifications] Status: NAD Editorial Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2008-02-25
View all other issues in [structure.specifications].
View all issues with NAD Editorial status.
Discussion:
The Remark clauses newly introduced into the Working Paper (N2134) are not mentioned in 17.5.1.4 [structure.specifications] where we list the meaning of Effects, Requires, and other clauses (with the exception of Notes which are documented as informative in 17.5.1.2 [structure.summary], p2, and which they replace in many cases).
Propose add a bullet for Remarks along with a brief description.
[ Batavia: Alan and Pete to work. ]
[ Bellevue: Already resolved in current working paper. ]
Proposed resolution:
Section: 18.6.1.1 [new.delete.single] Status: NAD Submitter: P.J. Plauger Opened: 2007-01-23 Last modified: 2008-02-25
View all other issues in [new.delete.single].
View all issues with NAD status.
Discussion:
I recognize the need for nothrow guarantees in the exception reporting mechanism, but I strongly believe that implementors also need an escape hatch when memory gets really low. (Like, there's not enough heap to construct and copy exception objects, or not enough stack to process the throw.) I'd like to think we can put this escape hatch in 18.6.1.1 [new.delete.single], operator new, but I'm not sure how to do it. We need more than a footnote, but the wording has to be a bit vague. The idea is that if new can't allocate something sufficiently small, it has the right to abort/call terminate/call unexpected.
[ Bellevue: NAD. 1.4p2 specifies a program must behave correctly "within its resource limits", so no further escape hatch is necessary. ]
Proposed resolution:
Section: 23.2 [container.requirements] Status: NAD Submitter: Lionel B Opened: 2007-02-01 Last modified: 2009-07-15
View other active issues in [container.requirements].
View all other issues in [container.requirements].
View all issues with NAD status.
Discussion:
A recent news group discussion:
Anyone know if the Standard has anything to say about the time complexity of size() for std::set? I need to access a set's size (/not/ to know if it is empty!) heavily during an algorithm and was thus wondering whether I'd be better off tracking the size "manually" or whether that'd be pointless.
That would be pointless. size() is O(1).
Nit: the standard says "should" have constant time. Implementations may take license to do worse. I know that some do this for std::list<> as a part of some trade-off with other operation.
I was aware of that, hence my reluctance to use size() for std::set.
However, this reason would not apply to std::set<> as far as I can see.
Ok, I guess the only option is to try it and see...
If I have any recommendation to the C++ Standards Committee it is that implementations must (not "should"!) document clearly[1], where known, the time complexity of *all* container access operations.
[1] In my case (gcc 4.1.1) I can't swear that the time complexity of size() for std::set is not documented... but if it is it's certainly well hidden away.
[ Kona (2007): This issue affects all the containers. We'd love to see a paper dealing with the broad issue. We think that the complexity of the size() member of every container -- except possibly list -- should be O(1). Alan has volunteered to provide wording. ]
[ Bellevue: ]
Mandating O(1) size will not fly, too many implementations would be invalidated. Alan to provide wording that toughens wording, but that does not absolutely mandate O(1).
[ Batavia (2009-05): ]
We observed that the wording "should" (in note a) has no effect. Howard prefers that O(1) size be mandated. It is not clear that this issue can be resolved to everyone's satisfaction, but Alan will provide wording nonetheless.
[ 2009-07 Frankfurt ]
Fixed by paper N2923.
Proposed resolution:
Section: 20.7.15.2.5 [func.wrap.func.targ] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-02-03 Last modified: 2007-07-02
View all issues with NAD Editorial status.
Discussion:
20.7.15.2.5 [func.wrap.func.targ], p4 says:
Returns: If type() == typeid(T), a pointer to the stored function target; otherwise a null pointer.
Proposed resolution:
Change 20.7.15.2.5 [func.wrap.func.targ], p4:
Returns: If
type()target_type() == typeid(T) && typeid(T) != typeid(void), a pointer to the stored function target; otherwise a null pointer.
[ Pete: Agreed. It's editorial, so I'll fix it. ]
Section: 26.6.2.3 [valarray.access] Status: NAD Editorial Submitter: Bo Persson Opened: 2007-02-11 Last modified: 2007-07-02
View all other issues in [valarray.access].
View all issues with NAD Editorial status.
Discussion:
The signature of the const operator[] has been changed to return a const reference.
The description in paragraph 1 still says that the operator returns by value.
[ Pete recommends editorial fix. ]
Proposed resolution:
Section: 26.8 [c.math] Status: NAD Editorial Submitter: Bo Persson Opened: 2007-02-13 Last modified: 2007-07-26
View all other issues in [c.math].
View all issues with NAD Editorial status.
Discussion:
26.8 [c.math], paragraph 10 has long lists of added signatures for float and long double functions. All the signatures have float/long double return values, which is inconsistent with some of the double functions they are supposed to overload.
Proposed resolution:
Change 26.8 [c.math], paragraph 10,
floatint ilogb(float);floatlong lrint(float);floatlong lround(float);floatlong long llrint(float);floatlong long llround(float);long doubleint ilogb(long double);long doublelong lrint(long double);long doublelong lround(long double);long doublelong long llrint(long double);long doublelong long llround(long double);
Section: 27.7.1.2.3 [istream::extractors], 27.7.2.6.3 [ostream.inserters] Status: NAD Submitter: Daniel Krügler Opened: 2007-02-17 Last modified: 2007-10-10
View all other issues in [istream::extractors].
View all issues with NAD status.
Discussion:
There already exist two active DR's for the wording of 27.7.1.2.3 [istream::extractors]/13 from 14882:2003(E), namely 64 and 413.
Even with these proposed corrections, already maintained in N2134, I have the feeling, that the current wording does still not properly handle the "exceptional" situation. The combination of para 14
"[..] Characters are extracted and inserted until any of the following occurs:
[..]
- an exception occurs (in which case the exception is caught)."
and 15
"If the function inserts no characters, it calls setstate(failbit), which may throw ios_base::failure (27.4.4.3). If it inserted no characters because it caught an exception thrown while extracting characters from *this and failbit is on in exceptions() (27.4.4.3), then the caught exception is rethrown."
both in N2134 seems to imply that any exception, which occurs *after* at least one character has been inserted is caught and lost for ever. It seems that even if failbit is on in exceptions() rethrow is not allowed due to the wording "If it inserted no characters because it caught an exception thrown while extracting".
Is this behaviour by design?
I would like to add that its output counterpart in 27.7.2.6.3 [ostream.inserters]/7-9 (also N2134) does not demonstrate such an exception-loss-behaviour. On the other side, I wonder concerning several subtle differences compared to input::
1) Paragraph 8 says at its end:
"- an exception occurs while getting a character from sb."
Note that there is nothing mentioned which would imply that such an exception will be caught compared to 27.7.1.2.3 [istream::extractors]/14.
2) Paragraph 9 says:
"If the function inserts no characters, it calls setstate(failbit) (which may throw ios_base::failure (27.4.4.3)). If an exception was thrown while extracting a character, the function sets failbit in error state, and if failbit is on in exceptions() the caught exception is rethrown."
The sentence starting with "If an exception was thrown" seems to imply that such an exception *should* be caught before.
Proposed resolution:
(a) In 27.7.1.2.3 [istream::extractors]/15 (N2134) change the sentence
If the function inserts no characters, it calls setstate(failbit), which may throw ios_base::failure (27.4.4.3). If
it inserted no characters because it caught an exception thrown while extracting characters from *thisan exception was thrown while extracting a character from *this, the function sets failbit in error state, and failbit is on in exceptions() (27.4.4.3), then the caught exception is rethrown.
(b) In 27.7.2.6.3 [ostream.inserters]/8 (N2134) change the sentence:
Gets characters from sb and inserts them in *this. Characters are read from sb and inserted until any of the following occurs:
- end-of-file occurs on the input sequence;
- inserting in the output sequence fails (in which case the character to be inserted is not extracted);
- an exception occurs while getting a character from sb (in which case the exception is caught).
Rationale:
This extractor is described as a formatted input function so the exception behavior is already specified. There is additional behavior described in this section that applies to the case in which failbit is set. This doesn't contradict the usual exception behavior for formatted input functions because that applies to the case in which badbit is set.Section: 27.7.4 [ext.manip] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-02-18 Last modified: 2007-07-02
View all other issues in [ext.manip].
View all issues with NAD Editorial status.
Discussion:
The function f in para 4 (27.7.4 [ext.manip]) references an unknown strm in the following line:
mg.get(Iter(str.rdbuf()), Iter(), intl, strm, err, mon);
Proposed resolution:
Change 27.7.4 [ext.manip], p4:
mg.get(Iter(str.rdbuf()), Iter(), intl, strm, err, mon);
[ Oxford: Editorial. ]
Section: 27.9.1.9 [ifstream.members], 27.9.1.13 [ofstream.members] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-02-20 Last modified: 2007-07-02
View all other issues in [ifstream.members].
View all issues with NAD Editorial status.
Discussion:
The standard wording of N2134 has extended the 14882:2003(E) wording for the ifstream/ofstream/fstream open function to fix a long standing problem, see 409.
Now it's properly written as
"If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit)[..]"
instead of the previous
"If that function returns a null pointer, calls setstate(failbit)[..]
While the old footnotes saying
"A successful open does not change the error state."
where correct and important, they are invalid now for ifstream and ofstream (because clear *does* indeed modify the error state) and should be removed (Interestingly fstream itself never had these, although they where needed for that time).
Proposed resolution:
In 27.9.1.9 [ifstream.members], remove footnote:
334) A successful open does not change the error state.
In 27.9.1.13 [ofstream.members], remove footnote:
335) A successful open does not change the error state.
Section: 20.7.15.2 [func.wrap.func] Status: NAD Submitter: Bo Persson Opened: 2007-02-25 Last modified: 2009-07-13
View all other issues in [func.wrap.func].
View all issues with NAD status.
Discussion:
20.7.15.2 [func.wrap.func]
The note in paragraph 2 refers to 'undefined void operators', while the section declares a pair of operators returning bool.
[ Post-Sophia Antipolis: ]
Changed from Pending WP to Open. This issue was voted to WP at the same time the operators were changed from private to deleted. The two issues stepped on each other. What do we want the return type of these deleted functions to be?
[ 2009-05-02 Daniel adds: ]
I suggest harmonizing this issue with similar classes. E.g. in 20.8.12.3 [util.smartptr.weak] bool return values for
template <class Y> bool operator<(weak_ptr<Y> const&) const = delete; template <class Y> bool operator<=(weak_ptr<Y> const&) const = delete; template <class Y> bool operator>(weak_ptr<Y> const&) const = delete; template <class Y> bool operator>=(weak_ptr<Y> const&) const = delete;are used and basically all newer provided deleted copy assignment operators of type X use the canonical return type X& instead of void. Since the note mentioned in the issue description has now already been changed to
deleted overloads close possible hole in the type systemit seems to be of even lesser need to perform the change. Therefore I recommend declaring the issue as NAD.
[ Batavia (2009-05): ]
We agree with Daniel's recommendation.
Move to NAD.
Proposed resolution:
Change 20.7.15.2 [func.wrap.func]
... private: // 20.7.15.2 [func.wrap.func], undefined operators: template<class Function2>boolvoid operator==(const function<Function2>&); template<class Function2>boolvoid operator!=(const function<Function2>&); };
Change 20.7.15.2 [func.wrap.func]
template<class Function2>boolvoid operator==(const function<Function2>&); template<class Function2>boolvoid operator!=(const function<Function2>&);
Section: 28.10 [re.results] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-02-26 Last modified: 2008-03-12
View all other issues in [re.results].
View all issues with NAD Editorial status.
Discussion:
According to the description given in 28.10 [re.results]/2 the class template match_results "shall satisfy the requirements of a Sequence, [..], except that only operations defined for const-qualified Sequences are supported". Comparing the provided operations from 28.10 [re.results]/3 with the sequence/container tables 80 and 81 one recognizes the following missing operations:
1) The members
const_iterator rbegin() const; const_iterator rend() const;
should exists because 23.1/10 demands these for containers (all sequences are containers) which support bidirectional iterators. Aren't these supported by match_result? This is not explicitely expressed, but it's somewhat implied by two arguments:
(a) Several typedefs delegate to iterator_traits<BidirectionalIterator>.
(b) The existence of const_reference operator[](size_type n) const implies even random-access iteration. I also suggest, that match_result should explicitly mention, which minimum iterator category is supported and if this does not include random-access the existence of operator[] is somewhat questionable.
2) The new "convenience" members
const_iterator cbegin() const; const_iterator cend() const; const_iterator crbegin() const; const_iterator crend() const;
should be added according to tables 80/81.
Proposed resolution:
Add the following members to the match_results synopsis after end() in 28.10 [re.results] para 3:
const_iterator cbegin() const; const_iterator cend() const;
In section 28.10.3 [re.results.acc] change:
const_iterator begin() const; const_iterator cbegin() const;-7- Returns: A starting iterator that enumerates over all the sub-expressions stored in *this.
const_iterator end() const; const_iterator cend() const;-8- Returns: A terminating iterator that enumerates over all the sub-expressions stored in *this.
[ Kona (2007): Voted to adopt proposed wording in N2409 except removing the entry in the table container requirements. Moved to Review. ]
[ Bellevue: Proposed wording now in the WP. ]
Section: 28.11.3 [re.alg.search] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-02-26 Last modified: 2007-07-26
View all issues with NAD Editorial status.
Discussion:
28.11.3 [re.alg.search]/5 declares
template <class iterator, class charT, class traits>
bool regex_search(iterator first, iterator last,
const basic_regex<charT, traits>& e,
regex_constants::match_flag_type flags =
regex_constants::match_default);
where it's not explained, which iterator category the parameter iterator belongs to. This is inconsistent to the preceding declaration in the synopsis section 28.4 [re.syn], which says:
template <class BidirectionalIterator, class charT, class traits>
bool regex_search(BidirectionalIterator first, BidirectionalIterator last,
const basic_regex<charT, traits>& e,
regex_constants::match_flag_type flags =
regex_constants::match_default);
Proposed resolution:
In 28.11.3 [re.alg.search]/5 replace all three occurences of param "iterator" with "BidirectionalIterator"
template <classiteratorBidirectionalIterator, class charT, class traits> bool regex_search(iteratorBidirectionalIterator first,iteratorBidirectionalIterator last, const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);-6- Effects: Behaves "as if" by constructing an object what of type match_results<
iteratorBidirectionalIterator> and then returning the result of regex_search(first, last, what, e, flags).
Rationale:
Applied to working paper while issue was still in New status.Section: 28.12.1.1 [re.regiter.cnstr] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-03-03 Last modified: 2007-07-02
View all issues with NAD Editorial status.
Discussion:
In 28.12.1.1 [re.regiter.cnstr]/2 the effects paragraph starts with:
Effects: Initializes begin and end to point to the beginning and the end of the target sequence, sets pregex to &re, sets flags to f,[..]
There are two issues with this description:
Proposed resolution:
In 28.12.1.1 [re.regiter.cnstr]/2 change the above quoted part by
Effects: Initializes begin and end to point to the beginning and the end of the target sequence designated by the iterator range [a, b), sets pregex to &re, sets flags to
fm, then calls regex_search(begin, end, match, *pregex, flags). If this call returns false the constructor sets *this to the end-of-sequence iterator.
Section: 28.12.2.1 [re.tokiter.cnstr] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-03-03 Last modified: 2007-07-02
View all other issues in [re.tokiter.cnstr].
View all issues with NAD Editorial status.
Discussion:
In 28.12.2.1 [re.tokiter.cnstr]/1+2 both the constructor declaration and the following text shows some obvious typos:
1) The third constructor form is written as
template <std::size_t N>
regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
const regex_type& re,
const int (&submatches)[R],
regex_constants::match_flag_type m =
regex_constants::match_default);
where the dimensions of submatches are specified by an unknown value R, which should be N.
2) Paragraph 2 of the same section says in its last sentence:
The third constructor initializes the member subs to hold a copy of the sequence of integer values pointed to by the iterator range [&submatches, &submatches + R).
where again R must be replaced by N.
3) Paragraph 3 of the same section says in its first sentence:
Each constructor then sets N to 0, and position to position_iterator(a, b, re, f).
where a non-existing parameter "f" is mentioned, which must be replaced by the parameter "m".
Proposed resolution:
Change 28.12.2.1 [re.tokiter.cnstr]/1:
template <std::size_t N>
regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
const regex_type& re,
const int (&submatches)[R N],
regex_constants::match_flag_type m =
regex_constants::match_default);
Change 28.12.2.1 [re.tokiter.cnstr]/2:
Effects: The first constructor initializes the member subs to hold the single value submatch. The second constructor initializes the member subs to hold a copy of the argument submatches. The third constructor initializes the member subs to hold a copy of the sequence of integer values pointed to by the iterator range [&submatches, &submatches +
RN).
Change 28.12.2.1 [re.tokiter.cnstr]/3:
Each constructor then sets N to 0, and position to position_iterator(a, b, re,
fm). If position is not an end-of-sequence iterator the constructor sets result to the address of the current match. Otherwise if any of the values stored in subs is equal to -1 the constructor sets *this to a suffix iterator that points to the range [a, b), otherwise the constructor sets *this to an end-of-sequence iterator.
Section: 1.2 [intro.refs] Status: NAD Submitter: Alisdair Meredith Opened: 2007-03-08 Last modified: 2008-02-25
View all other issues in [intro.refs].
View all issues with NAD status.
Discussion:
1.2 [intro.refs] Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this Interna- tional Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
- Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999.
- ISO/IEC 2382 (all parts), Information technology - Vocabulary
- ISO/IEC 9899:1990, Programming languages - C
- ISO/IEC 9899/Amd.1:1995, Programming languages - C, AMENDMENT 1: C Integrity
- ISO/IEC 9899:1999, Programming languages - C
- ISO/IEC 9899:1999/Cor.1:2001 Programming languages - C
- ISO/IEC 9899:1999/Cor.2:2004 Programming languages - C
- ISO/IEC 9945:2003, Information Technology-Portable Operating System Interface (POSIX)
- ISO/IEC 10646-1:1993 Information technology - Universal Multiple-Octet Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual Plane
I'm not sure how many of those reserve naming patterns that might affect us, but I am equally sure I don't own a copy of any of these to check!
The point is to list the reserved naming patterns, rather than the individual names themselves - although we may want to list C keywords that are valid identifiers in C++ but likely to cause trouble in shared headers (e.g. restrict)
[ Kona (2007): Recommend NAD. No one has identified a specific defect, just the possibility of one. ]
[
Post-Kona: Alisdair request Open. A good example of the problem was a
discussion of the system error proposal, where it was pointed out an all-caps
identifier starting with a capital E conflicted with reserved macro names for
both Posix and C. I had absolutely no idea of this rule, and suspect I was
not the only one in the room.
Resolution will require someone with access to all the listed documents to
research their respective name reservation rules, or people with access to
specific documents add their rules to this issue until the list is complete.
]
[ Bellevue: Wording is aleady present in various standards, and no-one has come forward with wording. Suggest a formal paper rather than a defect report is the correct way to proceed. ]
Proposed resolution:
Section: 26.5.1 [rand.synopsis] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-03-08 Last modified: 2007-07-02
View all other issues in [rand.synopsis].
View all issues with NAD Editorial status.
Discussion:
26.5.1 [rand.synopsis] the header <random> synopsis contains an unreasonable closing curly brace inside the subtract_with_carry_engine declaration.
Proposed resolution:
Change the current declaration in 26.5.1 [rand.synopsis]
template <class UIntType, size_t w}, size_t s, size_t r> class subtract_with_carry_engine;
[ Pete: Recommends editorial. ]
Section: 17.6.2.2 [using.headers] Status: NAD Submitter: Gennaro Prota Opened: 2007-03-14 Last modified: 2007-10-10
View all issues with NAD status.
Discussion:
17.6.2.2 [using.headers] states:
A translation unit shall include a header only outside of any external declaration or definition, [...]
I see three problems with this requirement:
The C++ standard doesn't define what an "external declaration" or an "external definition" are (incidentally the C99 standard does, and has a sentence very similar to the above regarding header inclusion).
I think the intent is that the #include directive shall lexically appear outside *any* declaration; instead, when the issue was pointed out on comp.std.c++ at least one poster interpreted "external declaration" as "declaration of an identifier with external linkage". If this were the correct interpretation, then the two inclusions below would be legal:
// at global scope
static void f()
{
# include <cstddef>
}
static void g()
{
# include <stddef.h>
}
(note that while the first example is unlikely to compile correctly, the second one may well do)
as the sentence stands, violations will require a diagnostic; is this the intent? It was pointed out on comp.std.c++ (by several posters) that at least one way to ensure a diagnostic exists:
[If there is an actual file for each header,] one simple way to implement this would be to insert a reserved identifier such as __begin_header at the start of each standard header. This reserved identifier would be ignored for all other purposes, except that, at the appropriate point in phase 7, if it is found inside an external definition, a diagnostic is generated. There's many other similar ways to achieve the same effect.
--James Kuyper, on comp.std.c++
is the term "header" meant to be limited to standard headers? Clause 17 is all about the library, but still the general question is interesting and affects one of the points in the explicit namespaces proposal (n1691):
Those seeking to conveniently enable argument-dependent lookups for all operators within an explicit namespace could easily create a header file that does so:
namespace mymath:: { #include "using_ops.hpp" }
Proposed resolution:
Rationale:
We believe that the existing language does not cause any real confusion and any new formulation of the rules that we could come up with are unlikely to be better than what's already in the standard.Section: 20.7 [function.objects] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-03-19 Last modified: 2007-08-05
View all other issues in [function.objects].
View all issues with NAD Editorial status.
Discussion:
The header <functional> synopsis in 20.7 [function.objects] contains the following two free comparison operator templates for the function class template
template<class Function1, class Function2> void operator==(const function<Function1>&, const function<Function2>&); template<class Function1, class Function2> void operator!=(const function<Function1>&, const function<Function2>&);
which are nowhere described. I assume that they are relicts before the corresponding two private and undefined member templates in the function template (see 20.7.15.2 [func.wrap.func] and [func.wrap.func.undef]) have been introduced. The original free function templates should be removed, because using an undefined entity would lead to an ODR violation of the user.
Proposed resolution:
Remove the above mentioned two function templates from the header <functional> synopsis (20.7 [function.objects])
template<class Function1, class Function2> void operator==(const function<Function1>&, const function<Function2>&); template<class Function1, class Function2> void operator!=(const function<Function1>&, const function<Function2>&);
Rationale:
Fixed by N2292 Standard Library Applications for Deleted Functions.Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: NAD Submitter: Cosmin Truta Opened: 2007-04-05 Last modified: 2007-07-25
View other active issues in [facet.num.get.virtuals].
View all other issues in [facet.num.get.virtuals].
View all issues with NAD status.
Discussion:
From Section 22.4.2.1.2 [facet.num.get.virtuals], paragraphs 11 and 12, it is implied
that the value read from a stream must be stored
even if the placement of thousands separators does not conform to the
grouping() specification from the numpunct facet.
Since incorrectly-placed thousands separators are flagged as an extraction
failure (by the means of failbit), we believe it is better not
to store the value. A consistent strategy, in which any kind of extraction
failure leaves the input item intact, is conceptually cleaner, is able to avoid
corner-case traps, and is also more understandable from the programmer's point
of view.
Here is a quote from "The C++ Programming Language (Special Edition)" by B. Stroustrup (Section D.4.2.3, pg. 897):
"If a value of the desired type could not be read, failbit is set in r. [...] An input operator will use r to determine how to set the state of its stream. If no error was encountered, the value read is assigned through v; otherwise, v is left unchanged."
This statement implies that rdstate() alone is sufficient to
determine whether an extracted value is to be assigned to the input item
val passed to do_get. However, this is in disagreement
with the current C++ Standard. The above-mentioned assumption is true in all
cases, except when there are mismatches in digit grouping. In the latter case,
the parsed value is assigned to val, and, at the same time, err
is assigned to ios_base::failbit (essentially "lying" about the
success of the operation). Is this intentional? The current behavior raises
both consistency and usability concerns.
Although digit grouping is outside the scope of scanf (on which
the virtual methods of num_get are based), handling of grouping
should be consistent with the overall behavior of scanf. The specification of
scanf makes a distinction between input failures and matching
failures, and yet both kinds of failures have no effect on the input items
passed to scanf. A mismatch in digit grouping logically falls in
the category of matching failures, and it would be more consistent, and less
surprising to the user, to leave the input item intact whenever a failure is
being signaled.
The extraction of bool is another example outside the scope of
scanf, and yet consistent, even in the event of a successful
extraction of a long but a failed conversion from
long to bool.
Inconsistency is further aggravated by the fact that, when failbit is set,
subsequent extraction operations are no-ops until failbit is
explicitly cleared. Assuming that there is no explicit handling of
rdstate() (as in cin>>i>>j) it is
counter-intuitive to be able to extract an integer with mismatched digit
grouping, but to be unable to extract another, properly-formatted integer
that immediately follows.
Moreover, setting failbit, and selectively assigning a value to
the input item, raises usability problems. Either the strategy of
scanf (when there is no extracted value in case of failure), or
the strategy of the strtol family (when there is always an
extracted value, and there are well-defined defaults in case of a failure) are
easy to understand and easy to use. On the other hand, if failbit
alone cannot consistently make a difference between a failed extraction, and a
successful but not-quite-correct extraction whose output happens to be the same
as the previous value, the programmer must resort to implementation tricks.
Consider the following example:
int i = old_i;
cin >> i;
if (cin.fail())
// can the value of i be trusted?
// what does it mean if i == old_i?
// ...
Last but not least, the current behvaior is not only confusing to the casual
reader, but it has also been confusing to some book authors. Besides
Stroustrup's book, other books (e.g. "Standard C++ IOStreams and Locales" by
Langer and Kreft) are describing the same mistaken assumption. Although books
are not to be used instead of the standard reference, the readers of these
books, as well as the people who are generally familiar to scanf,
are even more likely to misinterpret the standard, and expect the input items
to remain intact when a failure occurs.
Proposed resolution:
Change 22.4.2.1.2 [facet.num.get.virtuals]:
Stage 3: The result of stage 2 processing can be one of
- A sequence of
charshas been accumulated in stage 2 that is converted (according to the rules ofscanf) to a value of the type ofval.This value is stored invalandios_base::goodbitis stored inerr.- The sequence of
charsaccumulated in stage 2 would have causedscanfto report an input failure.ios_base::failbitis assigned toerr.In the first case,
Ddigit grouping is checked. That is, the positions of discarded separators is examined for consistency withuse_facet<numpunct<charT> >(loc).grouping(). If they are not consistent thenios_base::failbitis assigned toerr. Otherwise, the value that was converted in stage 2 is stored invalandios_base::goodbitis stored inerr.
Rationale:
post-Toronto: Changed from New to NAD at the request of the author. The preferred solution of N2327 makes this resolution obsolete.Section: 17.5.1.4 [structure.specifications] Status: NAD Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2009-05-01
View all other issues in [structure.specifications].
View all issues with NAD status.
Discussion:
17.5.1.4 [structure.specifications] para 5 says
-5- Complexity requirements specified in the library clauses are upper bounds, and implementations that provide better complexity guarantees satisfy the requirements.
The following objection has been raised:
The library clauses suggest general guidelines regarding complexity, but we have been unable to discover any absolute hard-and-fast formulae for these requirements. Unless or until the Library group standardizes specific hard-and-fast formulae, we regard all the complexity requirements as subject to a "fudge factor" without any intrinsic upper bound.
[Plum ref _23213Y31 etc]
Proposed resolution:
Rationale:
Kona (2007): No specific instances of underspecification have been identified, and big-O notation always involves constant factors.Section: 22.4.6.1.2 [locale.money.get.virtuals] Status: NAD Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2009-07-13
View other active issues in [locale.money.get.virtuals].
View all other issues in [locale.money.get.virtuals].
View all issues with NAD status.
Discussion:
22.4.6.1.2 [locale.money.get.virtuals], para 1 says:
The result is returned as an integral value stored in units or as a sequence of digits possibly preceded by a minus sign (as produced by ct.widen(c) where c is '-' or in the range from '0' through '9', inclusive) stored in digits.
The following objection has been raised:
Some implementations interpret this to mean that a facet derived from ctype<wchar_t> can provide its own member do_widen(char) which produces e.g. L'@' for the "widened" minus sign, and that the '@' symbol will appear in the resulting sequence of digits. Other implementations have assumed that one or more places in the standard permit the implementation to "hard-wire" L'-' as the "widened" minus sign. Are both interpretations permissible, or only one?
[Plum ref _222612Y14]
Furthermore: if ct.widen('9') produces L'X' (a non-digit), does a parse fail if a '9' appears in the subject string? [Plum ref _22263Y33]
[ Kona (2007): Bill and Dietmar to provide proposed wording. ]
[ post Bellevue: Bill adds: ]
The Standard is clear that the minus sign stored in digits is ct.widen('-'). The subject string must contain characters c in the set [-0123456789] which are translated by ct.widen(c) calls before being stored in digits; the widened characters are not relevant to the parsing of the subject string.
[ Batavia (2009-05): ]
We agree with Bill's comment above, in line with the first of the interpretations offered in the issue. Move to NAD.
Proposed resolution:
Section: 22.4.6.1.2 [locale.money.get.virtuals] Status: NAD Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2009-07-13
View other active issues in [locale.money.get.virtuals].
View all other issues in [locale.money.get.virtuals].
View all issues with NAD status.
Discussion:
22.4.6.1.2 [locale.money.get.virtuals], para 3 sentence 4 says:
If the first character of pos is equal to the first character of neg, or if both strings are empty, the result is given a positive sign.
One interpretation is that an input sequence must match either the positive pattern or the negative pattern, and then in either event it is interpreted as positive. The following objections has been raised:
The input can successfully match only a positive sign, so the negative pattern is an unsuccessful match.
[Plum ref _222612Y34, 222612Y51b]
[ Bill to provide proposed wording and interpretation of existing wording. ]
[ 2009-05-17 See Howard's comments in related issue 668. ]
[ Batavia (2009-05): ]
This discussion applies equally to issue 668 (q.v.). Howard has added examples there, and recommends either NAD or a resolution that adds his (or similar) examples to the Working Paper.
We recommend moving to NAD. Anyone who feels strongly about adding the examples is invited to submit corresponding wording. We further recommend issue 668 be handled identically.
Proposed resolution:
Section: 22.4.6.3 [locale.moneypunct] Status: Dup Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2008-09-22
View all issues with Dup status.
Duplicate of: 836
Discussion:
22.4.6.3 [locale.moneypunct], para 2 says:
The value space indicates that at least one space is required at that position.
The following objection has been raised:
Whitespace is optional when matching space. (See 22.4.6.1.2 [locale.money.get.virtuals], para 2.)
[Plum ref _22263Y22]
[ Kona (2007): Bill to provide proposed wording. We agree that C++03 is ambiguous, and that we want C++0X to say "space" means 0 or more whitespace characters on input. ]
Proposed resolution:
Section: 28.12.2 [re.tokiter] Status: NAD Editorial Submitter: Eric Niebler Opened: 2007-06-02 Last modified: 2009-03-09
View all other issues in [re.tokiter].
View all issues with NAD Editorial status.
Discussion:
28.12.2 [re.tokiter], p3 says:
After it is constructed, the iterator finds and stores a value match_results<BidirectionalIterator> position and sets the internal count N to zero.
Should read:
After it is constructed, the iterator finds and stores a value
match_resultsregex_iterator<BidirectionalIterator, charT, traits> position and sets the internal count N to zero.
[ John adds: ]
Yep, looks like a typo/administrative fix to me.
Proposed resolution:
Section: 28.10 [re.results] Status: NAD Editorial Submitter: Nozomu Katoo Opened: 2007-05-27 Last modified: 2008-03-12
View all other issues in [re.results].
View all issues with NAD Editorial status.
Discussion:
In 28.4 [re.syn] of N2284, two template functions are declared here:
// 28.10, class template match_results:
<snip>
// match_results comparisons
template <class BidirectionalIterator, class Allocator>
bool operator== (const match_results<BidirectionalIterator, Allocator>& m1,
const match_results<BidirectionalIterator, Allocator>& m2);
template <class BidirectionalIterator, class Allocator>
bool operator!= (const match_results<BidirectionalIterator, Allocator>& m1,
const match_results<BidirectionalIterator, Allocator>& m2);
// 28.10.6, match_results swap:
But the details of these two bool operator functions (i.e., which members of match_results should be used in comparison) are not described in any following sections.
[ John adds: ]
That looks like a bug: operator== should return true only if the two objects refer to the same match - ie if one object was constructed as a copy of the other.
[ Kona (2007): Bill and Pete to add minor wording to that proposed in N2409. ]
Proposed resolution:
Add a new section after 28.10.6 [re.results.swap], which reads:
28.10.7 match_results non-member functions.
template<class BidirectionalIterator, class Allocator> bool operator==(const match_results<BidirectionalIterator, Allocator>& m1, const match_results<BidirectionalIterator, Allocator>& m2);Returns: true only if the two objects refer to the same match.
template<class BidirectionalIterator, class Allocator> bool operator!=(const match_results<BidirectionalIterator, Allocator>& m1, const match_results<BidirectionalIterator, Allocator>& m2);Returns: !(m1 == m2).
template<class BidirectionalIterator, class Allocator> void swap(match_results<BidirectionalIterator, Allocator>& m1, match_results<BidirectionalIterator, Allocator>& m2);Returns: m1.swap(m2).
[ Bellevue: Proposed wording now in WP. ]
Section: 20.8.11.2.4 [unique.ptr.single.observers], 20.8.12.2.5 [util.smartptr.shared.obs] Status: NAD Submitter: Beman Dawes Opened: 2007-06-14 Last modified: 2008-02-27
View all issues with NAD status.
Discussion:
The standard library uses the operator unspecified-bool-type() const idiom in five places. In three of those places (20.7.15.2.3 [func.wrap.func.cap], function capacity for example) the returned value is constrained to disallow unintended conversions to int. The standardese is
The return type shall not be convertible to int.
This constraint is omitted for unique_ptr and shared_ptr. It should be added for those.
[ Bellevue: ]
Close as NAD. Accepting paper N2435 makes it irrelevant.
Proposed resolution:
To the Returns paragraph for operator unspecified-bool-type() const of 20.8.11.2.4 [unique.ptr.single.observers] paragraph 11 and 20.8.12.2.5 [util.smartptr.shared.obs] paragraph 16, add the sentence:
The return type shall not be convertible to int.
[ Kona (2007): Uncertain if nullptr will address this issue. ]
Section: 26.8 [c.math] Status: NAD Editorial Submitter: Niels Dekker Opened: 2007-06-10 Last modified: 2007-07-25
View all other issues in [c.math].
View all issues with NAD Editorial status.
Discussion:
Quoting the latest draft (n2135), 26.8 [c.math]:
The added signatures are:
long abs(long); // labs() long abs(long long); // llabs()
Shouldn't abs(long long) have long long as return type?
Proposed resolution:
Change 26.8 [c.math]:
long long abs(long long); // llabs()
Rationale:
Had already been fixed in the WP by the time the LWG reviewed this.Section: 19.5 [syserr] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-06-24 Last modified: 2008-01-06
View all other issues in [syserr].
View all issues with NAD Editorial status.
Discussion:
The most recent state of N2241 as well as the current draft N2284 (section 19.5 [syserr], p.2) proposes a new enumeration type posix_errno immediatly in the namespace std. One of the enumerators has the name invalid_argument, or fully qualified: std::invalid_argument. This name clashes with the exception type std::invalid_argument, see 19.2 [std.exceptions]/p.3. This clash makes e.g. the following snippet invalid:
#include <system_error>
#include <stdexcept>
void foo() { throw std::invalid_argument("Don't call us - we call you!"); }
I propose that this enumeration type (and probably the remaining parts of <system_error> as well) should be moved into one additional inner namespace, e.g. sys or system to reduce foreseeable future clashes due to the great number of members that std::posix_errno already contains (Btw.: Why has the already proposed std::sys sub-namespace from N2066 been rejected?). A further clash candidate seems to be std::protocol_error (a reasonable name for an exception related to a std network library, I guess).
Another possible resolution would rely on the proposed strongly typed enums, as described in N2213. But maybe the forbidden implicit conversion to integral types would make these enumerators less attractive in this special case?
Proposed resolution:
Fixed by issue 7 of N2422.
Section: TR1 5.2.1.1 [tr.num.sf.Lnm] Status: NAD Submitter: Christopher Crawford Opened: 2007-06-30 Last modified: 2009-07-13
View all issues with NAD status.
Discussion:
I see that the definition the associated Laguerre polynomials TR1 5.2.1.1 [tr.num.sf.Lnm] has been corrected since N1687. However, the draft standard only specifies ranks of integer value m, while the associated Laguerre polynomials are actually valid for real values of m > -1. In the case of non-integer values of m, the definition Ln(m) = (1/n!)exx-m (d/dx)n (e-xxm+n) must be used, which also holds for integer values of m. See Abramowitz & Stegun, 22.11.6 for the general case, and 22.5.16-17 for the integer case. In fact fractional values are most commonly used in physics, for example to m = +/- 1/2 to describe the harmonic oscillator in 1 dimension, and 1/2, 3/2, 5/2, ... in 3 dimensions.
If I am correct, the calculation of the more general case is no more difficult, and is in fact the function implemented in the GNU Scientific Library. I would urge you to consider upgrading the standard, either adding extra functions for real m or switching the current ones to double.
[ Batavia (2009-05): ]
We understand the issue, and have opted not to extend as recommended.
Move to NAD.
Proposed resolution:
Section: TR1 5.2.1.2 [tr.num.sf.Plm] Status: NAD Submitter: Christopher Crawford Opened: 2007-06-30 Last modified: 2009-07-13
View all issues with NAD status.
Discussion:
One other small thing, in TR1 5.2.1.2 [tr.num.sf.Plm], the restriction should be |x| <= 1, not x >= 0.
[ Batavia (2009-05): ]
The error has been corrected in the pending IS.
Move to NAD.
Proposed resolution:
Section: 18.8.5 [propagation] Status: NAD Submitter: Jens Maurer Opened: 2007-07-20 Last modified: 2008-02-25
View other active issues in [propagation].
View all other issues in [propagation].
View all issues with NAD status.
Discussion:
From the Toronto Core wiki:
What do you mean by "null pointer constant"? How do you guarantee that exception_ptr() == 1 doesn't work? Do you even want to prevent that? What's the semantics? What about void *p = 0; exception_ptr() == p? Maybe disallow those in the interface, but how do you do that with portable C++? Could specify just "make it work".
Peter's response:
null pointer constant as defined in 4.10 [conv.ptr]. Intent is "just make it work", can be implemented as assignment operator taking a unique pointer to member, as in the unspecified bool type idiom.
[ Bellevue: ]
Original implementation was possible using the "unspecified-null-pointer" idiom, similar to unspecified-bool.
Even simpler now with nullptr_t.
NAD Rationale : null pointer constant is a perfectly defined term, and while API is clearly implementable there is no need to spell out implementation details.
Proposed resolution:
Section: 22 [localization] Status: NAD Future Submitter: Peter Dimov Opened: 2007-07-28 Last modified: 2009-07-16
View all other issues in [localization].
View all issues with NAD Future status.
Discussion:
The POSIX "Extended API Set Part 4,"
introduces extensions to the C locale mechanism that allow multiple concurrent locales to be used in the same application by introducing a type locale_t that is very similar to std::locale, and a number of _l functions that make use of it.
The global locale (set by setlocale) is now specified to be per- process. If a thread does not call uselocale, the global locale is in effect for that thread. It can install a per-thread locale by using uselocale.
There is also a nice querylocale mechanism by which one can obtain the name (such as "de_DE") for a specific facet, even for combined locales, with no std::locale equivalent.
std::locale should be harmonized with the new POSIX locale_t mechanism and provide equivalents for uselocale and querylocale.
[ Kona (2007): Bill and Nick to provide wording. ]
[ San Francisco: Bill and Nick still intend to provide wording, but this is a part of the task to be addressed by the group that will look into issue 860. ]
[ 2009-07 Frankfurt: ]
It's our intention to stay in sync with WG14. If WG14 makes a decision that requires a change in WG21 the issue will be reopened.
Move to NAD Future.
Proposed resolution:
Section: 26.6.2.3 [valarray.access] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-08-27 Last modified: 2008-09-22
View all other issues in [valarray.access].
View all issues with NAD Editorial status.
Discussion:
Since the return type of valarray's operator[] const overload has been changed to const T& as described in 389 several paragraphs of the section 26.6.2.3 [valarray.access] are now incompletely specified, because many requirements and guarantees should now also apply to the const overload. Most notably, the address and reference guarantees should be extended to the const overload case.
Proposed resolution:
Change 26.6.2.3 [valarray.access]:
-1-
When applied to a constant array, the subscript operator returns a reference to the corresponding element of the array. When applied to a non-constant array, tThe subscript operator returns a reference to the corresponding element of the array.-3- The expression &a[i+j] == &a[i] + j evaluates as true for all size_t i and size_t j such that i+j is less than the length of the
non-constantarray a.-4- Likewise, the expression &a[i] != &b[j] evaluates as true for any two
non-constantarrays a and b and for any size_t i and size_t j such that i is less than the length of a and j is less than the length of b. This property indicates an absence of aliasing and may be used to advantage by optimizing compilers.281)-5- The reference returned by the subscript operator for an
non-constantarray is guaranteed to be valid until the member function resize(size_t, T) (26.5.2.7) is called for that array or until the lifetime of that array ends, whichever happens first.
Section: 21.4 [basic.string] Status: NAD Editorial Submitter: Bo Persson Opened: 2007-08-18 Last modified: 2009-07-16
View all other issues in [basic.string].
View all issues with NAD Editorial status.
Discussion:
Paragraph 21.4 [basic.string]/3 states:
The class template basic_string conforms to the requirements for a Sequence (23.1.1) and for a Reversible Container (23.1).
First of all, 23.2.3 [sequence.reqmts] is no longer "Sequence" but "Sequence container". Secondly, after the resent changes to containers (emplace, push_back, const_iterator parameters to insert and erase), basic_string is not even close to conform to the current requirements.
[ Bellevue: ]
- emplace, for example, may not make sense for strings. Is also likely suboptimal
- with concepts do we need to maintain string as sequence container?
- One approach might be to say something like: string is a sequence except it doesn't have these functions
General consensus is to suggest option 2.
- basic_string already has push_back
- const_iterator parameters to insert and erase should be added to basic_string
- this leaves emplace to handle -- we have the following options:
- option 1: add it to string even though it's optional
- option 2: make emplace optional to sequences (move from table 89 to 90)
- option 3: say string not sequence (the proposal),
- option 4: add an exception to basic string wording.
[ 2009-07 Frankfurt: ]
Move to NAD Editorial
Proposed resolution:
Remove this sentence, in recognition of the fact that basic_string is not just a vector-light for literal types, but something quite different, a string abstraction in its own right.
Section: 22.3.3.2.2 [conversions.string] Status: NAD Submitter: Bo Persson Opened: 2007-08-27 Last modified: 2009-07-16
View all other issues in [conversions.string].
View all issues with NAD status.
Discussion:
Paragraph 3 says that the Codecvt template parameter shall meet the requirements of std::codecvt, even though std::codecvt itself cannot be used (because of a protected destructor).
How are we going to explain this code to beginning programmers?
template<class I, class E, class S>
struct codecvt : std::codecvt<I, E, S>
{
~codecvt()
{ }
};
void main()
{
std::wstring_convert<codecvt<wchar_t, char, std::mbstate_t> > compiles_ok;
std::wstring_convert<std::codecvt<wchar_t, char, std::mbstate_t> > not_ok;
}
[ San Francisco: ]
Bill will propose a resolution.
[ 2009-07 Frankfurt: ]
codecvt isn't intended for beginning programmers. This is a regrettable consequence of the original design of the facet.
Move to NAD.
Proposed resolution:
Section: 23.2.3 [sequence.reqmts] Status: NAD Editorial Submitter: David Abrahams Opened: 2007-09-16 Last modified: 2008-09-22
View all other issues in [sequence.reqmts].
View all issues with NAD Editorial status.
Discussion:
Table 90: (Optional sequence container operations) states the "assertion note pre/post-condition" of operator[] to be
*(a.begin() + n)
Surely that's meant to be "operational semantics?"
Proposed resolution:
Table 90: Optional sequence container operations expression return type assertion/note
pre/post-condition
operational semanticscontainer
Section: X [rand.req.eng] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-02-27
View all other issues in [rand.req.eng].
View all issues with NAD status.
Discussion:
The 3rd table row in X [rand.req.eng]/3 requires random number engines to accept any arithmetic type as a seed, which is then casted to the engine's result_type and subsequently used for seeding the state of the engine. The requirement stated as "Creates an engine with initial state determined by static_cast<X::result_type>(s)" forces random number engines to either use a seeding method that completely depends on the result_type (see the discussion of seeding for the mersenne_twister_engine in point T2 above) or at least to throw away "bits of randomness" in the seed value if the result_type is smaller than the seed type. This seems to be inappropriate for many modern random number generators, in particular F2-linear or cryptographic ones, which operate on an internal bit array that in principle is independent of the type of numbers returned.
Posible resolution: I propose to change the wording to a version similar to "Creates an engine with initial state determined by static_cast<UintType>(s), where UintType is an implementation specific unsigned integer type."
Additionally, the definition of s in X [rand.req.eng]/1 c) could be restricted to unsigned integer types.
Similarly, the type of the seed in X [rand.req.adapt]/3 e) could be left unspecified.
See N2424 for further discussion.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In reply to the discussion in N2424 regarding this issue:
The descriptions of all engines and engine adaptors given in sections 26.5.3 [rand.eng] and 26.5.4 [rand.adapt] already specify the concrete types of the integer arguments for seeding. Hence, relaxing the general requirement in X [rand.req.eng] would not affect portability and reproducibility of the standard library. Furthermore, it is not clear to me what exactly the guarantee "with initial state determined by static_cast<X::result_type>(s)" is useful for. On the other hand, relaxing the requirement would allow developers to implement other random number engines that do not have to cast all arithmetic seed arguments to their result_types.
[ Bellevue: ]
Propose close NAD for the reasons given in N2424.
Proposed resolution:
See N2424 for further discussion.
[ Stephan Tolksdorf adds pre-Bellevue: ]
Change row 3 of table 105 "Random number engine requirements" in X [rand.req.eng]/3
Creates an engine with initial state determined bystatic_cast<X::result_type>(s)Similarly, change X [rand.req.adapt]/3 e)
When X::X is invoked withan X::result_typevalue s of arithmetic type (3.9.1), ...
Section: X [rand.req.adapt] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-02-27
View all issues with NAD status.
Discussion:
If an engine adaptor is invoked with an argument of type seed_seq, then all base engines are specified to be seeded with this seed_seq. As seed_seq's randomization method is qualified as constant, this procedure will ef fectively initialize all base engines with the same seed (though the resulting state might still dif fer to a certain degree if the engines are of different types). It is not clear whether this mode of operation is in general appropriate, hence -- as far as the stated requirements are of general nature and not just specific to the engine adaptors provided by the library -- it might be better to leave the behaviour unspecified, since the current definition of seed_seq does not allow for a generally satisfying specification.
Posssible resolution: [As above]
See N2424 for further discussion.
[ Bellevue: ]
Close NAD for the reasons given in N2424.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.5.7.1 [rand.util.seedseq] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-02-27
View all other issues in [rand.util.seedseq].
View all issues with NAD status.
Discussion:
The proper way to seed random number engines seems to be the most frequently discussed issue of the 26.5 [rand] proposal. While the new seed_seq approach is already rather general and probably sufficient for most situations, it is unlikely to be optimal in every case (one problem was pointed out in point T5 above). In some situations it might, for instance, be better to seed the state with a cryptographic generator.
In my opinion this is a pretty strong argument for extending the standard with a simple facility to customize the seeding procedure. This could, for example, be done with the following minimal changes:
Possible resolution:
Supplement the seed_seq with a traits class
template <typename T>
struct is_seed_seq { static const bool value = false; }
and the specialization
template <>
struct is_seed_seq<seed_seq> { static const bool value = true; }
which users can supplement with further specializations.
[ Bellevue: ]
See N2424. Close NAD but note that "conceptizing" the library may cause this problem to be solved by that route.
Proposed resolution:
See N2424 for the proposed resolution.
Section: X [rand.dist.samp.genpdf] Status: NAD Editorial Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2009-03-09
View all other issues in [rand.dist.samp.genpdf].
View all issues with NAD Editorial status.
Duplicate of: 795
Discussion:
X [rand.dist.samp.genpdf] describes the interface for a distribution template that is meant to simulate random numbers from any general distribution given only the density and the support of the distribution. I'm not aware of any general purpose algorithm that would be capable of correctly and efficiently implementing the described functionality. From what I know, this is essentially an unsolved research problem. Existing algorithms either require more knowledge about the distribution and the problem domain or work only under very limited circumstances. Even the state of the art special purpose library UNU.RAN does not solve the problem in full generality, and in any case, testing and customer support for such a library feature would be a nightmare.
Possible resolution: For these reasons, I propose to delete section X [rand.dist.samp.genpdf].
[ Bellevue: ]
Disagreement persists.
Objection to this issue is that this function takes a general functor. The general approach would be to normalize this function, integrate it, and take the inverse of the integral, which is not possible in general. An example function is sin(1+n*x) -- for any spatial frequency that the implementor chooses, there is a value of n that renders that choice arbitrarily erroneous.
Correction: The formula above should instead read 1+sin(n*x).
Objector proposes the following possible compromise positions:
- rand.dist.samp.genpdf takes an number of points so that implementor need not guess.
- replace rand.disk.samp.genpdf with an extension to either or both of the discrete functions to take arguments that take a functor and number of points in place of the list of probabilities. Reference issues 793 and 794.
Proposed resolution:
See N2813 for the proposed resolution.
Rationale:
Addressed by N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X".Section: X [rand.req.dist] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-02-27
View all issues with NAD status.
Discussion:
The requirement "P shall have a declaration of the form typedef X distribution_- type" effectively makes the use of inheritance for implementing distributions very inconvenient, because the child of a distribution class in general will not satisfy this requirement. In my opinion the benefits of having a typedef in the parameter class pointing back to the distribution class are not worth the hassle this requirement causes. [In my code base I never made use of the nested typedef but on several occasions could have profited from being able to use simple inheritance for the implementation of a distribution class.]
Proposed resolution: I propose to drop this requirement.
[ Bellevue: ]
Close NAD for the reasons given in N2424. In practice it is not inconvenient to meet these requirements.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.5.8.2.2 [rand.dist.bern.bin], 26.5.8.2.4 [rand.dist.bern.negbin] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-02-27
View all issues with NAD status.
Discussion:
In my opinion the choice of name for the t parameter of the binomial_distribution is very unfortunate. In virtually every internet reference, book and software implementation this parameter is called n instead, see for example Wikipedia, Mathworld, Evans et al. (1993) Statistical Distributions, 2nd E., Wiley, p. 38, the R statistical computing language, p. 926, Mathematica and Matlab.
Similarly, the choice of k for the parameter of the negative binomial distributions is rather unusual. The most common choice for the negative binomial distribution seems to be r instead.
Choosing unusual names for the parameters causes confusion among users and makes the interface unnecessarily inconvenient to use.
Possible resolution: For these reasons, I propose to change the name of the respective parameters to n and r.
[ Bellevue: ]
In N2424. NAD It has been around for a while. It is hardly universal, there is prior art, and this would confuse people.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.5.8.5.1 [rand.dist.samp.discrete] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-02-27
View all other issues in [rand.dist.samp.discrete].
View all issues with NAD status.
Discussion:
Possible resolution: I propose to change the specification such that the non-standardized probabilities need to be returned and that an additional requirement is included for the number of probabilities to be smaller than the maximum of IntType.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In reply to the discussion in N2424 of this issue:
Rescaled floating-point parameter vectors can not be expected to compare equal because of the limited precision of floating-point numbers. My proposal would at least guarantee that a parameter vector (of type double) passed into the distribution would compare equal with the one returned by the probabilities() method. Furthermore, I do not understand why "the changed requirement would lead to a significant increase in the amount of state in the distribution object". A typical implementation's state would increase by exactly one number: the sum of all probabilities. The textual representation for serialization would not need to grow at all. Finally, the proposed replacement "0 < n <= numeric_limits<IntType>::max() + 1" makes the implementation unnecessarily complicated, "0 < n <= numeric_limits<IntType>::max()" would be better.
[ Bellevue: ]
In N2424. We agree with the observation and the proposed resolution to part b). We recommend the wording n > 0 be replaced with 0 < n numeric_limits::max() + 1. However, we disagree with part a), as it would interfere with the definition of parameters' equality. Further, the changed requirement would lead to a significant increase in the amount of state of the distribution object.
As it stands now, it is convenient, and the changes proposed make it much less so.
NAD. Part a the current behavior is desirable. Part b, any constructor can fail, but the rules under which it can fail do not need to be listed here.
Proposed resolution:
See N2424 for the proposed resolution.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In 26.5.8.5.1 [rand.dist.samp.discrete]:
Proposed wording a):
Changae in para. 2
Constructs a discrete_distribution object with n=1 and p0 = w0 = 1and change in para. 5
Returns: A vector<double> whose size member returns n and whose operator[] member returnspkthe weight wk as a double value when invoked with argument k for k = 0, ..., n-1Proposed wording b):
Change in para. 3:
If firstW == lastW, let the sequence w have length n = 1 and consist of the single value w0 = 1. Otherwise, [firstW,lastW) shall form a sequence w of length n> 0such that 0 < n <= numeric_limits<IntType>::max(), and *firstW shall yield a value w0 convertible to double. [Note: The values wk are commonly known as the weights . -- end note]
Section: 26.5.8.5.2 [rand.dist.samp.pconst] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-02-27
View all other issues in [rand.dist.samp.pconst].
View all issues with NAD status.
Discussion:
The design of the constructor
template <class InputIteratorB, class InputIteratorW>
piecewise_constant_distribution( InputIteratorB firstB, InputIteratorB lastB,
InputIteratorW firstW);
is unnecessarily unsafe, as there is no separate end-iterator given for the weights. I can't see any performance or convenience reasons that would justify the risks inherent in such a function interface, in particular the risk that input error might go unnoticed.
Possible resolution: I propose to add an InputIteratorW lastW argument to the interface.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In reply to the discussion in N2424 I'd like to make the same comments as for 736.
[ Bellevue: ]
In N2424. There is already precedent elsewhere in the library. Follows existing convention. NAD.
Proposed resolution:
See N2424 for the proposed resolution.
[ Stephan Tolksdorf adds pre-Bellevue: ]
In 26.5.8.5.2 [rand.dist.samp.pconst]:
Proposed wording a)
Change in para. 2
Constructs a piecewise_constant_distribution object with n = 1, p0 = w0 = 1, b0 = 0, and b1 = 1and change in para. 5
A vector<result_type> whose size member returns n and whose operator[] member returnspkthe weight wk as a double value when invoked with argument k for k = 0, ..., n-1Proposed wording b)
Change both occurrences of
"piecewise_constant_distribution(InputIteratorB firstB, InputIteratorB lastB, InputIteratorW firstW, InputIteratorW lastW)and change in para. 3
the length of the sequence w starting from firstW shall be at least n, *firstW shall return a value w0 that is convertible to double, and any wk for k >= n shall be ignored by the distribution[firstW, lastW) shall form a sequence w of length n whose leading element w0 shall be convertible to double
Section: 26.5.4.1 [rand.adapt.disc] Status: NAD Editorial Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-09-22
View all issues with NAD Editorial status.
Discussion:
Since the template parameter p and r are of type size_t, the member n in the class exposition should have type size_t, too.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 26.5.7.2 [rand.util.canonical] Status: NAD Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-02-27
View all other issues in [rand.util.canonical].
View all issues with NAD status.
Discussion:
The complexity of generate_canonical is specified to be "exactly k=max(1, ceil(b/log2 R)) invocations of g". This terms involves a logarithm that is not rounded and hence can not (in general) be computed at compile time. As this function template is performance critical, I propose to replace ceil(b/log2 R) with ceil(b/floor(log2 R)).
See N2424 for further discussion.
[ Bellevue: ]
In N2424. Close NAD as described there.
Proposed resolution:
See N2424 for the proposed resolution.
Section: 20.8.12.2.11 [util.smartptr.getdeleter] Status: NAD Submitter: Daniel Krügler Opened: 2007-09-27 Last modified: 2008-02-27
View all other issues in [util.smartptr.getdeleter].
View all issues with NAD status.
Discussion:
The following issue was raised by Alf P. Steinbach in c.l.c++.mod:
According to the recent draft N2369, both the header memory synopsis of 20.8 [memory] and 20.8.12.2.11 [util.smartptr.getdeleter] declare:
template<class D, class T> D* get_deleter(shared_ptr<T> const& p);
This allows to retrieve the pointer to a mutable deleter of a const shared_ptr (if that owns one) and therefore contradicts the usual philosophy that associated functors are either read-only (e.g. key_comp or value_comp of std::map) or do at least reflect the mutability of the owner (as seen for the both overloads of unique_ptr::get_deleter). Even the next similar counter-part of get_deleter - the two overloads of function::target in the class template function synopsis 20.7.15.2 [func.wrap.func] or in 20.7.15.2.5 [func.wrap.func.targ] - do properly mirror the const-state of the owner.
Possible proposed resolutions:Replace the declarations of get_deleter in the header <memory> synopsis of 20.8 [memory] and in 20.8.12.2.11 [util.smartptr.getdeleter] by one of the following alternatives (A) or (B):
template<class D, class T> const D* get_deleter(shared_ptr<T> const& p);
Alberto Ganesh Barbati adds:
Replace it with two functions:
template <class D, class T> D get_deleter(shared_ptr<T> const&); template <class D, class T> bool has_deleter(shared_ptr<T> const&);
The first one would throw if D is the wrong type, while the latter would never throw. This approach would reflect the current praxis of use_facet/has_facet, with the twist of returning the deleter by value as container::get_allocator() do.
Peter Dimov adds:
My favorite option is "not a defect". A, B and C break useful code.
[ Bellevue: ]
Concern this is similar to confusing "pointer to const" with "a constant pointer".
Proposed resolution:
Section: 18.8.5 [propagation] Status: NAD Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2008-02-25
View other active issues in [propagation].
View all other issues in [propagation].
View all issues with NAD status.
Discussion:
It could be I did not understand the design rationale, but I thought copy_exception would produce an exception_ptr to the most-derived (dynamic) type of the passed exception. Instead it slices, which appears to be less useful, and a likely source of FAQ questions in the future.
(Peter Dimov suggests NAD)
[ Bellevue: ]
How could this be implemented in a way that the dynamic type is cloned?
The feature is designed to create an exception_ptr from an object whose static type is identical to the dynamic type and thus there is no slicing involved.
Proposed resolution:
Section: 20.6.4.3 [meta.unary.prop] Status: NAD Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2009-07-16
View other active issues in [meta.unary.prop].
View all other issues in [meta.unary.prop].
View all issues with NAD status.
Discussion:
We have 3 separate type traits to identify classes supporting no-throw operations, which are very useful when trying to provide exception safety guarantees. However, I'm not entirely clear on what the current wording requires of a conforming implementation. To quote from has_nothrow_default_constructor:
or T is a class type with a default constructor that is known not to throw any exceptions
What level of magic do we expect to deduce if this is known?
E.g.
struct test{
int x;
test() : x() {}
};
Should I expect a conforming compiler to assert( has_nothrow_constructor<test>::value )
Is this a QoI issue?
Should I expect to 'know' only if-and-only-if there is an inline definition available?
Should I never expect that to be true, and insist that the user supplies an empty throw spec if they want to assert the no-throw guarantee?
It would be helpful to maybe have a footnote explaining what is required, but right now I don't know what to suggest putting in the footnote.
(agreement since is that trivial ops and explicit no-throws are required. Open if QoI should be allowed to detect further)
[ Bellevue: ]
This looks like a QoI issue. In the case of trivial and nothrow it is known. Static analysis of the program is definitely into QoI. Move to OPEN. Need to talk to Core about this.
[ 2009-07 Frankfurt: ]
This is QoI.
Move to NAD.
Proposed resolution:
Section: 20.6.4.3 [meta.unary.prop] Status: NAD Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2009-05-01
View other active issues in [meta.unary.prop].
View all other issues in [meta.unary.prop].
View all issues with NAD status.
Discussion:
I am trying to decide is a pure virtual function is a necessary as well as sufficient requirement to be classified as abstract?
For instance, is the following (non-polymorphic) type considered abstract?
struct abstract {
protected:
abstract(){}
abstract( abstract const & ) {}
~abstract() {}
};
(Suggested that this may be NAD, with an editorial fix-up from Pete on the core wording to make clear that abstract requires a pure virtual function)
Proposed resolution:
Core has clarified that the definition abstract is adequate. Issue withdrawn by submitter. NAD.
Section: 20.6.5 [meta.rel] Status: Dup Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2009-09-13
View all other issues in [meta.rel].
View all issues with Dup status.
Duplicate of: 719
Discussion:
With the pending arrival of explicit conversion functions though, I'm wondering if we want an additional trait, is_explictly_convertible?
[ Bellevue: ]
Alisdair is considering preparing a paper listing a number of missing type traits, and feels that it might be useful to handle them all together rather than piecemeal. This would affect issue 719 and 750. These two issues should move to OPEN pending AM paper on type traits.
[ 2009-07 Frankfurt: ]
Duplicate of 719 (for our purposes).
[ Addressed in N2947. ]
Proposed resolution:
Section: 23.3.7 [vector.bool] Status: NAD Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2009-07-16
View all other issues in [vector.bool].
View all issues with NAD status.
Discussion:
A number of vector<bool> members take const bool& as arguments. Is there any chance we could change them to pass-by-value or would I be wasting everyone's time if wrote up an issue?
[ post Bellevue: ]
As we understand it, the original requester (Martin Sebor) would like for implementations to be permitted to pass-by-value. Alisdair suggests that if this is to be resolved, it should be resolved more generally, e.g. in other containers as well.
We note that this would break ABI. However, we also suspect that this might be covered under the "as-if" rule in section 1.9.
Many in the group feel that for vector<bool>, this is a "don't care", and that at this point in the process it's not worth the bandwidth.
Issue 679 -- which was in ready status pre-Bellevue and is now in the working paper -- is related to this, though not a duplicate.
Moving to Open with a task for Alisdair to craft a informative note to be put whereever appropriate in the WP. This note would clarify places where pass-by-const-ref can be transformed to pass-by-value under the as-if rule.
[ San Francisco: ]
This is really a clause 17 issue, rather than something specific to vector<bool>.
Move to Open. Alisdair to provide a resolution. Alternately, Howard can close this as NAD and then open a new issue to handle the general issue (rather than the vector<bool> one).
Howard: Haven't yet opened new issue. Lacking wording for it.
[ 2009-07 Frankfurt: ]
NAD. Insufficient motivation to make any changes.
Proposed resolution:
Section: 20.8.10.1 [uninitialized.copy] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2007-10-15 Last modified: 2008-07-02
View all other issues in [uninitialized.copy].
View all issues with NAD Editorial status.
Discussion:
14882-2003, [lib.uninitialized.copy] is currently written as follows:
template <class InputIterator, class ForwardIterator> ForwardIterator uninitialized_copy(InputIterator first, InputIterator last, ForwardIterator result);-1- Effects:
for (; first != last; ++result, ++first) new (static_cast<void*>(&*result)) typename iterator_traits<ForwardIterator>::value_type(*first);-2- Returns: result
similarily for N2369, and its corresponding section 20.8.10.1 [uninitialized.copy].
It's not clear to me what the return clause is supposed to mean, I see two possible interpretations:
The problem is: I see nothing in the standard which grants that this interpretation is correct, specifically [lib.structure.specifications] or 17.5.1.4 [structure.specifications] resp. do not clarify which "look-up" rules apply for names found in the elements of the detailed specifications - Do they relate to the corresponding synopsis or to the effects clause (or possibly other elements)? Fortunately most detailed descriptions are unambigious in this regard, e.g. this problem does not apply for std::copy.
Proposed resolution:
Change the wording of the return clause to say (20.8.10.1 [uninitialized.copy]):
-2- Returns: The value of result after effects have taken place.
[ Bellevue: ]
Resolution: NAD editorial -- project editor to decide if change is worthwhile. Concern is that there are many other places this might occur.
Section: 23.3.5 [container.adaptors] Status: NAD Editorial Submitter: Paolo Carlini Opened: 2007-10-31 Last modified: 2008-06-18
View other active issues in [container.adaptors].
View all other issues in [container.adaptors].
View all issues with NAD Editorial status.
Discussion:
After n2369 we have a single push_back overload in the sequence containers, of the "emplace" type. At variance with that, still in n2461, we have two separate overloads, the C++03 one + one taking an rvalue reference in the container adaptors. Therefore, simply from a consistency point of view, I was wondering whether the container adaptors should be aligned with the specifications of the sequence container themselves: thus have a single push along the lines:
template<typename... _Args>
void
push(_Args&&... __args)
{ c.push_back(std::forward<_Args>(__args)...); }
[ Related to 767 ]
Proposed resolution:
Change 23.3.5.1.1 [queue.defn]:
void push(const value_type& x) { c.push_back(x); }void push(value_type&& x) { c.push_back(std::move(x)); }template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
Change 23.3.5.2 [priority.queue]:
void push(const value_type& x) { c.push_back(x); }void push(value_type&& x) { c.push_back(std::move(x)); }template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
Change 23.3.5.2.2 [priqueue.members]:
void push(const value_type& x);
Effects:c.push_back(x);push_heap(c.begin(), c.end(), comp);template<class... Args> void push(value_typeArgs&&...xargs);Effects:
c.push_back(std::moveforward<Args>(xargs)...); push_heap(c.begin(), c.end(), comp);
Change 23.3.5.3.1 [stack.defn]:
void push(const value_type& x) { c.push_back(x); }void push(value_type&& x) { c.push_back(std::move(x)); }template<class... Args> void push(Args&&... args) { c.push_back(std::forward<Args>(args)...); }
Rationale:
Addressed by N2680 Proposed Wording for Placement Insert (Revision 1).
Section: 23.3.6 [vector] Status: NAD Editorial Submitter: Paolo Carlini Opened: 2007-11-04 Last modified: 2008-07-02
View other active issues in [vector].
View all other issues in [vector].
View all issues with NAD Editorial status.
Discussion:
In the synopsis 23.3.6 [vector], there is the signature:
void insert(const_iterator position, size_type n, T&& x);
instead of:
iterator insert(const_iterator position, T&& x);
23.3.6.4 [vector.modifiers] is fine.
Proposed resolution:
Change the synopsis in 23.3.6 [vector]:
iterator insert(const_iterator position, const T& x); iterator insert(const_iterator position, T&& x); void insert(const_iterator position, size_type n, const T& x);void insert(const_iterator position, size_type n, T&& x);
Section: 23.2 [container.requirements] Status: NAD Future Submitter: Paolo Carlini Opened: 2007-11-11 Last modified: 2009-07-17
View other active issues in [container.requirements].
View all other issues in [container.requirements].
View all issues with NAD Future status.
Discussion:
In an emplace member function the function parameter pack may be bound to a priori unlimited number of objects: some or all of them can be elements of the container itself. Apparently, in order to conform to the blanket statement 23.2 [container.requirements]/11, the implementation must check all of them for that possibility. A possible solution can involve extending the exception in 23.2 [container.requirements]/12 also to the emplace member. As a side note, the push_back and push_front member functions are luckily not affected by this problem, can be efficiently implemented anyway
[ Related to 767 ]
[ Bellevue: ]
The proposed addition (13) is partially redundant with the existing paragraph 12. Why was the qualifier "rvalues" added to paragraph 12? Why does it not cover subelements and pointers?
Resolution: Alan Talbot to rework language, then set state to Review.
[ 2009-07 Frankfurt ]
The problem is broader than emplace. The LWG doesn't feel that it knows how to write wording that prohibits all of the problematic use cases at this time.
NAD Future.
Proposed resolution:
Add after 23.2 [container.requirements]/12:
-12- Objects passed to member functions of a container as rvalue references shall not be elements of that container. No diagnostic required.
-13- Objects bound to the function parameter pack of the emplace member function shall not be elements or sub-objects of elements of the container. No diagnostic required.
Section: 23.2.4 [associative.reqmts] Status: NAD Submitter: Sylvain Pion Opened: 2007-12-04 Last modified: 2008-03-12
View other active issues in [associative.reqmts].
View all other issues in [associative.reqmts].
View all issues with NAD status.
Discussion:
The associative containers provide 2 overloads of emplace():
template <class... Args> pair<iterator, bool> emplace(Args&&... args); template <class... Args> iterator emplace(const_iterator position, Args&&... args);
This is a problem if you mean the first overload while passing a const_iterator as first argument.
[ Related to 767 ]
[ Bellevue: ]
This can be disambiguated by passing "begin" as the first argument in the case when the non-default choice is desired. We believe that desire will be rare.
Resolution: Change state to NAD.
Proposed resolution:
Rename one of the two overloads. For example to emplace_here, hint_emplace...
Section: 23.2.5 [unord.req] Status: NAD Submitter: Joe Gottman Opened: 2007-11-29 Last modified: 2008-03-12
View other active issues in [unord.req].
View all other issues in [unord.req].
View all issues with NAD status.
Discussion:
A major attribute of the unordered containers is that iterating though them inside a bucket is very fast while iterating between buckets can be much slower. If an unordered container has a low load factor, iterating between the last iterator in one bucket and the next iterator, which is in another bucket, is O(bucket_count()) which may be much larger than O(size()).
If b is an non-const unordered container of type B and k is an object of it's key_type, then b.equal_range(k) currently returns pair<B::iterator, B::iterator>. Consider the following code:
B::iterator lb, ub;
tie(lb, ub) = b.equal_range(k);
for (B::iterator it = lb; it != ub; ++it) {
// Do something with *it
}
If b.equal_range(k) returns a non-empty range (i.e. b contains at least on element whose key is equivalent to k), then every iterator in the half-open range [lb, ub) will be in the same bucket, but ub will likely either be in a different bucket or be equal to b.end(). In either case, iterating between ub - 1 and ub could take a much longer time than iterating through the rest of the range.
If instead of returning pair<iterator, iterator>, equal_range were to return pair<local_iterator, local_iterator>, then ub (which, like lb, would now be a local_iterator) could be guaranteed to always be in the same bucket as lb. In the cases where currently ub is equal to b.end() or is in a different bucket, ub would be equal to b.end(b.bucket(key)). This would make iterating between lb and ub much faster, as every iteration would be constant time.
[ Bellevue: ]
The proposed resolution breaks consistency with other container types for dubious benefit, and iterators are already constant time.
Proposed resolution:
Change the entry for equal_range in Table 93 (23.2.5 [unord.req]) as follows:
| expression | return type | assertion/note pre/post-condition | complexity |
|---|---|---|---|
| b.equal_range(k) | pair<local_iterator,local_iterator>; pair<const_local_iterator,const_local_iterator> for const b. | Returns a range containing all elements with keys equivalent to k. Returns make_pair(b.end(b.bucket(key)),b.end(b.bucket(key))) if no such elements exist. | Average case Θ(b.count(k)). Worst case Θ(b.size()). |
Section: 23 [containers] Status: NAD Editorial Submitter: Sylvain Pion Opened: 2007-12-28 Last modified: 2008-06-18
View other active issues in [containers].
View all other issues in [containers].
View all issues with NAD Editorial status.
Discussion:
Playing with g++'s C++0X mode, I noticed that the following code, which used to compile:
#include <vector>
int main()
{
std::vector<char *> v;
v.push_back(0);
}
now fails with the following error message:
.../include/c++/4.3.0/ext/new_allocator.h: In member function 'void __gnu_cxx::new_allocator<_Tp>::construct(_Tp*, _Args&& ...) [with _Args = int, _Tp = char*]': .../include/c++/4.3.0/bits/stl_vector.h:707: instantiated from 'void std::vector<_Tp, _Alloc>::push_back(_Args&& ...) [with _Args = int, _Tp = char*, _Alloc = std::allocator<char*>]' test.cpp:6: instantiated from here .../include/c++/4.3.0/ext/new_allocator.h:114: error: invalid conversion from 'int' to 'char*'
As far as I know, g++ follows the current draft here.
Does the committee really intend to break compatibility for such cases?
[ Sylvain adds: ]
I just noticed that std::pair has the same issue. The following now fails with GCC's -std=c++0x mode:
#include <utility> int main() { std::pair<char *, char *> p (0,0); }I have not made any general audit for such problems elsewhere.
[ Related to 756 ]
[ Bellevue: ]
Motivation is to handle the old-style int-zero-valued NULL pointers. Problem: this solution requires concepts in some cases, which some users will be slow to adopt. Some discussion of alternatives involving prohibiting variadic forms and additional library-implementation complexity.
Discussion of "perfect world" solutions, the only such solution put forward being to retroactively prohibit use of the integer zero for a NULL pointer. This approach was deemed unacceptable given the large bodies of pre-existing code that do use integer zero for a NULL pointer.
Another approach is to change the member names. Yet another approach is to forbid the extension in absence of concepts.
Resolution: These issues (756, 767, 760, 763) will be subsumed into a paper to be produced by Alan Talbot in time for review at the 2008 meeting in France. Once this paper is produced, these issues will be moved to NAD.
Proposed resolution:
Add the following rows to Table 90 "Optional sequence container operations", 23.2.3 [sequence.reqmts]:
expression return type assertion/note
pre-/post-conditioncontainer a.push_front(t) void a.insert(a.begin(), t)
Requires: T shall be CopyConstructible.list, deque a.push_front(rv) void a.insert(a.begin(), rv)
Requires: T shall be MoveConstructible.list, deque a.push_back(t) void a.insert(a.end(), t)
Requires: T shall be CopyConstructible.list, deque, vector, basic_string a.push_back(rv) void a.insert(a.end(), rv)
Requires: T shall be MoveConstructible.list, deque, vector, basic_string
Change the synopsis in 23.3.2 [deque]:
void push_front(const T& x); void push_front(T&& x); void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change 23.3.2.3 [deque.modifiers]:
void push_front(const T& x); void push_front(T&& x); void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change the synopsis in 23.3.4 [list]:
void push_front(const T& x); void push_front(T&& x); void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change 23.3.4.3 [list.modifiers]:
void push_front(const T& x); void push_front(T&& x); void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_front(Args&&... args); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change the synopsis in 23.3.6 [vector]:
void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Change 23.3.6.4 [vector.modifiers]:
void push_back(const T& x); void push_back(T&& x); template <class... Args> requires Constructible<T, Args&&...> void push_back(Args&&... args);
Rationale:
Addressed by N2680 Proposed Wording for Placement Insert (Revision 1).
If there is still an issue with pair, Howard should submit another issue.
Section: 26.5.8.1 [rand.dist.uni] Status: NAD Submitter: P.J. Plauger Opened: 2008-01-14 Last modified: 2008-02-27
View all other issues in [rand.dist.uni].
View all issues with NAD status.
Discussion:
[ Bellevue: ]
NAD. Withdrawn.
Proposed resolution:
Section: 30.4.3.2.3 [thread.lock.unique.mod] Status: NAD Submitter: Constantine Sapuntzakis Opened: 2008-02-02 Last modified: 2008-02-27
View all issues with NAD status.
Discussion:
unique_lock::release will probably lead to many mistakes where people call release instead of unlock. I just coded such a mistake using the boost pre-1.35 threads library last week.
In many threading libraries, a call with release in it unlocks the lock (e.g. ReleaseMutex in Win32, java.util.concurrent.Semaphore).
I don't call unique_lock::lock much at all, so I don't get to see the symmetry between ::lock and ::unlock. I usually use the constructor to lock the mutex. So I'm left to remember whether to call release or unlock during the few times I need to release the mutex before the scope ends. If I get it wrong, the compiler doesn't warn me.
An alternative name for release may be disown.
This might be a rare case where usability is hurt by consistency with the rest of the C++ standard (e.g. std::auto_ptr::release).
[ Bellevue: ]
Change a name from release to disown. However prior art uses the release name. Compatibility with prior art is more important that any possible benefit such a change might make. We do not see the benefit for changing. NAD
Proposed resolution:
Change the synopsis in 30.4.3.2 [thread.lock.unique]:
template <class Mutex>
class unique_lock
{
public:
...
mutex_type* release disown();
...
};
Change 30.4.3.2.3 [thread.lock.unique.mod]:
mutex_type *releasedisown();
Section: TR1 5.1.4.5 [tr.rand.eng.disc], TR1 5.1.4.6 [tr.rand.eng.xor] Status: NAD Submitter: John Maddock Opened: 2008-01-15 Last modified: 2009-07-13
View all issues with NAD status.
Discussion:
Table 16 of TR1 requires that all Pseudo Random Number generators have a
seed(integer-type s)
member function that is equivalent to:
mygen = Generator(s)
But the generators xor_combine and discard_block have no such seed member, only the
template <class Gen> seed(Gen&);
member, which will not accept an integer literal as an argument: something that appears to violate the intent of Table 16.
So... is this a bug in TR1?
This is a real issue BTW, since the Boost implementation does adhere to the requirements of Table 16, while at least one commercial implementation does not and follows a strict adherence to sections 5.1.4.5 and 5.1.4.6 instead.
[ Jens adds: ]
Both engines do have the necessary constructor, therefore the omission of the seed() member functions appears to be an oversight.
[ Post Summit Daniel adds: ]
Recommend NAD: xor_combine does no longer exist and discard_block[_engine] has now the required seed overload accepting a result_type, which shall be an unsigned integral type.
[ Batavia (2009-05): ]
Move to NAD as recommended.
Proposed resolution:
NAD Recommended.
Section: 20.9 [time] Status: NAD Editorial Submitter: Christopher Kohlhoff, Jeff Garland Opened: 2008-02-03 Last modified: 2008-09-30
View all other issues in [time].
View all issues with NAD Editorial status.
Discussion:
The draft C++0x thread library requires that the time points of type system_time and returned by get_system_time() represent Coordinated Universal Time (UTC) (section [datetime.system]). This can lead to surprising behavior when a library user performs a duration-based wait, such as condition_variable::timed_wait(). A complete explanation of the problem may be found in the Rationale for the Monotonic Clock section in POSIX, but in summary:
POSIX solves the problem by introducing a new monotonic clock, which is unaffected by changes to the system time. When a condition variable is initialized, the user may specify whether the monotonic clock is to be used. (It is worth noting that on POSIX systems it is not possible to use condition_variable::native_handle() to access this facility, since the desired clock type must be specified during construction of the condition variable object.)
In the context of the C++0x thread library, there are added dimensions to the problem due to the need to support platforms other than POSIX:
One possible minimal solution:
Proposed resolution:
Rationale:
Addressed by N2661: A Foundation to Sleep On.Section: X [rand.adapt.xor] Status: NAD Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2008-02-27
View all other issues in [rand.adapt.xor].
View all issues with NAD status.
Discussion:
xor_combine::seed(result_type) and seed(seed_seq&) don't say what happens to each of the sub-engine seeds. (Should probably do the same to both, unlike TR1.)
[ Bellevue: ]
Overcome by the previous proposal. NAD mooted by resolution of 789.
Proposed resolution:
Section: 26.5.8.5.2 [rand.dist.samp.pconst] Status: NAD Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2008-03-11
View all other issues in [rand.dist.samp.pconst].
View all issues with NAD status.
Discussion:
piecewise_constant_distribution::densities() should be probabilities(), just like discrete_distribution. (There's no real use for weights divided by areas.)
[ Bellevue: ]
Fermilab does not agree with this summary. As defined in the equation in 26.4.8.5.2/4, the quantities are indeed probability densities not probabilities. Because we view this distribution as a parameterization of a *probability density function*, we prefer to work in terms of probability densities.
We don't think this should be changed.
If there is a technical argument about why the implementation dealing with these values can't be as efficient as one dealing with probabilities, we might reconsider. We don't care about this one member function being somewhat more or less efficient; we care about the size of the distribution object and the speed of the calls to generate variates.
Proposed resolution:
Change synopsis in 26.5.8.5.2 [rand.dist.samp.pconst]:
template <class RealType = double>
class piecewise_constant_distribution
{
public:
...
vector<double> densities probabilities() const;
...
};
Change 26.5.8.5.2 [rand.dist.samp.pconst]/6:
vector<double>densitiesprobabilities() const;
Section: 26.5.8.5.1 [rand.dist.samp.discrete] Status: NAD Editorial Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2009-03-09
View all other issues in [rand.dist.samp.discrete].
View all issues with NAD Editorial status.
Discussion:
discrete_distribution should have a constructor like:
template<class _Fn>
discrete_distribution(result_type _Count, double _Low, double _High,
_Fn& _Func);
(Makes it easier to fill a histogram with function values over a range.)
[ Bellevue: ]
How do you specify the function so that it does not return negative values? If you do it is a bad construction. This requirement is already there. Where in each bin does one evaluate the function? In the middle. Need to revisit tomorrow.
[ Sophia Antipolis: ]
Bill is not requesting this.
Marc Paterno: _Fn cannot return negative values at the points where the function is sampled. It is sampled in the middle of each bin. _Fn cannot return 0 everywhere it is sampled.
Jens: lambda expressions are rvalues
Add a library issue to provide an initializer_list<double> constructor for discrete_distribution.
Marc Paterno: dislikes reference for _Fn parameter. Make it pass-by-value (to use lambda), use std::ref to wrap giant-state function objects.
Daniel: See random_shuffle, pass-by-rvalue-reference.
Daniel to draft wording.
[ Pre San Francisco, Daniel provided wording: ]
The here proposed changes of the WP refer to the current state of N2691. During the Sophia Antipolis meeting two different proposals came up regarding the functor argument type, either by value or by rvalue-reference. For consistence with existing conventions (state-free algorithms and the general_pdf_distribution c'tor signature) the author decided to propose a function argument that is provided by value. If severe concerns exists that stateful functions would be of dominant relevance, it should be possible to replace the two occurrences of Func by Func&& in this proposal as part of an editorial process.
Proposed resolution:
Non-concept version of the proposed resolution
In 26.5.8.5.1 [rand.dist.samp.discrete]/1, class discrete_distribution, just before the member declaration
explicit discrete_distribution(const param_type& parm);
insert:
template<typename Func> discrete_distribution(result_type nf, double xmin, double xmax, Func fw);
Between p.4 and p.5 insert a series of new paragraphs as part of the new member description::
template<typename Func> discrete_distribution(result_type nf, double xmin, double xmax, Func fw);Complexity: Exactly nf invocations of fw.
Requires:
- fw shall be callable with one argument of type double, and shall return values of a type convertible to double;
- If nf > 0, the relation xmin < xmax shall hold, and for all sample values xk, fw(xk) shall return a weight value wk that is non-negative, non-NaN, and non-infinity;
- The following relations shall hold: nf ≥ 0, and 0 < S = w0+. . .+wn-1.
Effects:
- If nf == 0, sets n = 1 and lets the sequence w have length n = 1 and consist of the single value w0 = 1.
Otherwise, sets n = nf, deltax = (xmax - xmin)/n and xcent = xmin + 0.5 * deltax.
For each k = 0, . . . ,n-1, calculates: xk = xcent + k * deltax wk = fw(xk)Constructs a discrete_distribution object with probabilities:
pk = wk/S for k = 0, . . . , n-1.
Concept version of the proposed resolution
In 26.5.8.5.1 [rand.dist.samp.discrete]/1, class discrete_distribution, just before the member declaration
explicit discrete_distribution(const param_type& parm);
insert:
template<Callable<auto, double> Func> requires Convertible<Func::result_type, double> discrete_distribution(result_type nf, double xmin, double xmax, Func fw);
Between p.4 and p.5 insert a series of new paragraphs as part of the new member description::
template<Callable<auto, double> Func> requires Convertible<Func::result_type, double> discrete_distribution(result_type nf, double xmin, double xmax, Func fw);Complexity: Exactly nf invocations of fw.
Requires:
- If nf > 0, the relation xmin < xmax shall hold, and for all sample values xk, fw(xk) shall return a weight value wk that is non-negative, non-NaN, and non-infinity;
- The following relations shall hold: nf ≥ 0, and 0 < S = w0+. . .+wn-1.
Effects:
- If nf == 0, sets n = 1 and lets the sequence w have length n = 1 and consist of the single value w0 = 1.
Otherwise, sets n = nf, deltax = (xmax - xmin)/n and xcent = xmin + 0.5 * deltax.
For each k = 0, . . . ,n-1, calculates: xk = xcent + k * deltax wk = fw(xk)Constructs a discrete_distribution object with probabilities:
pk = wk/S for k = 0, . . . , n-1.
Rationale:
Addressed by N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X".Section: 26.5.8.5.2 [rand.dist.samp.pconst] Status: NAD Editorial Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2009-03-09
View all other issues in [rand.dist.samp.pconst].
View all issues with NAD Editorial status.
Discussion:
piecewise_constant_distribution should have a constructor like:
template<class _Fn>
piecewise_constant_distribution(size_t _Count,
_Ty _Low, _Ty _High, _Fn& _Func);
(Makes it easier to fill a histogram with function values over a range. The two (reference 793) make a sensible replacement for general_pdf_distribution.)
[ Sophia Antipolis: ]
Marc: uses variable width of bins and weight for each bin. This is not giving enough flexibility to control both variables.
Add a library issue to provide an constructor taking an initializer_list<double> and _Fn for piecewise_constant_distribution.
Daniel to draft wording.
[ Pre San Francisco, Daniel provided wording. ]
The here proposed changes of the WP refer to the current state of N2691. For reasons explained in 793, the author decided to propose a function argument that is provided by value. The issue proposes a c'tor signature, that does not take advantage of the full flexibility of piecewise_constant_distribution, because it restricts on a constant bin width, but the use-case seems to be popular enough to justify it's introduction.
Proposed resolution:
Non-concept version of the proposed resolution
In 26.5.8.5.2 [rand.dist.samp.pconst]/1, class piecewise_constant_distribution, just before the member declaration
explicit piecewise_constant_distribution(const param_type& parm);
insert:
template<typename Func> piecewise_constant_distribution(size_t nf, RealType xmin, RealType xmax, Func fw);
Between p.4 and p.5 insert a new sequence of paragraphs nominated below as [p5_1], [p5_2], [p5_3], and [p5_4] as part of the new member description:
template<typename Func> piecewise_constant_distribution(size_t nf, RealType xmin, RealType xmax, Func fw);[p5_1] Complexity: Exactly nf invocations of fw.
[p5_2] Requires:
- fw shall be callable with one argument of type RealType, and shall return values of a type convertible to double;
- For all sample values xk defined below, fw(xk) shall return a weight value wk that is non-negative, non-NaN, and non-infinity;
- The following relations shall hold: xmin < xmax, and 0 < S = w0+. . .+wn-1.
[p5_3] Effects:
If nf == 0,
- sets deltax = xmax - xmin, and
- lets the sequence w have length n = 1 and consist of the single value w0 = 1, and
- lets the sequence b have length n+1 with b0 = xmin and b1 = xmax
Otherwise,
- sets n = nf, deltax = (xmax - xmin)/n, xcent = xmin + 0.5 * deltax, and
lets the sequences w and b have length n and n+1, resp. and
for each k = 0, . . . ,n-1, calculates: dxk = k * deltax bk = xmin + dxk xk = xcent + dxk wk = fw(xk),and
- sets bn = xmax
Constructs a piecewise_constant_distribution object with the above computed sequence b as the interval boundaries and with the probability densities:
ρk = wk/(S * deltax) for k = 0, . . . , n-1.[p5_4] [Note: In this context, the subintervals [bk, bk+1) are commonly known as the bins of a histogram. -- end note]
Concept version of the proposed resolution
In 26.5.8.5.2 [rand.dist.samp.pconst]/1, class piecewise_constant_distribution, just before the member declaration
explicit piecewise_constant_distribution(const param_type& parm);
insert:
template<Callable<auto, RealType> Func> requires Convertible<Func::result_type, double> piecewise_constant_distribution(size_t nf, RealType xmin, RealType xmax, Func fw);
Between p.4 and p.5 insert a new sequence of paragraphs nominated below as [p5_1], [p5_2], [p5_3], and [p5_4] as part of the new member description:
template<Callable<auto, RealType> Func> requires Convertible<Func::result_type, double> piecewise_constant_distribution(size_t nf, RealType xmin, RealType xmax, Func fw);[p5_1] Complexity: Exactly nf invocations of fw.
[p5_2] Requires:
- For all sample values xk defined below, fw(xk) shall return a weight value wk that is non-negative, non-NaN, and non-infinity;
- The following relations shall hold: xmin < xmax, and 0 < S = w0+. . .+wn-1.
[p5_3] Effects:
If nf == 0,
- sets deltax = xmax - xmin, and
- lets the sequence w have length n = 1 and consist of the single value w0 = 1, and
- lets the sequence b have length n+1 with b0 = xmin and b1 = xmax
Otherwise,
- sets n = nf, deltax = (xmax - xmin)/n, xcent = xmin + 0.5 * deltax, and
lets the sequences w and b have length n and n+1, resp. and
for each k = 0, . . . ,n-1, calculates: dxk = k * deltax bk = xmin + dxk xk = xcent + dxk wk = fw(xk),and
- sets bn = xmax
Constructs a piecewise_constant_distribution object with the above computed sequence b as the interval boundaries and with the probability densities:
ρk = wk/(S * deltax) for k = 0, . . . , n-1.[p5_4] [Note: In this context, the subintervals [bk, bk+1) are commonly known as the bins of a histogram. -- end note]
Rationale:
Addressed by N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X".Section: X [rand.dist.samp.genpdf] Status: Dup Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2008-03-11
View all other issues in [rand.dist.samp.genpdf].
View all issues with Dup status.
Duplicate of: 732
Discussion:
general_pdf_distribution should be dropped. (It's a research topic in adaptive numerical integration.)
[ Stephan Tolksdorf notes: ]
This appears to be a duplicate of 732.
Proposed resolution:
Section: 26.5.5 [rand.predef] Status: NAD Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2008-02-27
View all other issues in [rand.predef].
View all issues with NAD status.
Discussion:
The 10,000th value returned by ranlux48_base is supposed to be 61839128582725. We get 192113843633948. (Note that the underlying generator was changed in Kona.)
[ Bellevue: ]
Submitter withdraws defect.
Proposed resolution:
Change 26.5.5 [rand.predef]/p5:
typedef subtract_with_carry_engine<uint_fast64_t, 48, 5, 12> ranlux48_base;Required behavior: The 10000th consecutive invocation of a default-constructed object of type ranlux48_base shall produce the value61839128582725192113843633948.
Section: 26.5.5 [rand.predef] Status: NAD Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2008-02-27
View all other issues in [rand.predef].
View all issues with NAD status.
Discussion:
The 10,000th value returned by ranlux48 is supposed to be 249142670248501. We get 88229545517833. (Note that this depends on ranlux48_base.)
[ Bellevue: ]
Submitter withdraws defect.
Proposed resolution:
Change 26.5.5 [rand.predef]/p6:
typedef discard_block_engine<ranlux48_base, 389, 11> ranlux48Required behavior: The 10000th consecutive invocation of a default-constructed object of type ranlux48 shall produce the value24914267024850188229545517833.
Section: 26.5.3.2 [rand.eng.mers], TR1 5.1.4.2 [tr.rand.eng.mers] Status: NAD Submitter: Stephan Tolksdorf Opened: 2008-02-18 Last modified: 2008-03-11
View all other issues in [rand.eng.mers].
View all issues with NAD status.
Discussion:
TR1 5.1.4.2 [tr.rand.eng.mers](10) requires that operator== for the mersenne_twister returns true if and only if the states of two mersenne_twisters, consisting each of n integers between 0 and 2w - 1, are completely equal. This is a contradiction with TR1 5.1.1 [tr.rand.req](3) because the given definition of the state also includes the lower r bits of x(i-n), which will never be used to generate a random number. If two mersenne_twisters only differ in the lower bits of x(i-n) they will not compare equal, although they will produce an identical sequence of random numbers.
26.5.3.2 [rand.eng.mers] in the latest C++ draft does not specify the behaviour of operator== but uses a similar definition of the state and, just like TR1 5.1.4.2 [tr.rand.eng.mers], requires the textual representation of a mersenne_twister_engine to consist of Xi-n to Xi-1, including the lower bits of Xi-n. This leads to two problems: First, the unsuspecting implementer is likely to erroneously compare the lower r bits of Xi-n in operator==. Second, if only the lower r bits differ, two mersenne_twister_engines will compare equal (if correctly implemented) but have different textual representations, which conceptually is a bit ugly.
I propose that a paragraph or footnote is added to 26.5.3.2 [rand.eng.mers] which clarifies that the lower r bits of Xi-n are not to be compared in operator== and operator!=. It would only be consequent if furthermore the specification for the textual respresentation was changed to Xi-n bitand ((2w - 1) - (2r - 1)), Xi-(n-1), ..., Xi-1 or something similar.
These changes would likely have no practical effect, but would allow an implementation that does the right thing to be standard-conformant.
[ Bellevue: ]
Fermi Lab has no objection to the proposed change. However it feels that more time is needed to check the details, which would suggest a change to REVIEW.
Bill feels that this is NAD, not enough practical importance to abandon the simple definition of equality, and someone would have to do a lot more study to ensure that all cases are covered for a very small payback. The submitter admits that "These changes would likely have no practical effect,", and according to Plum's razor this means that it is not worth the effort!
Revisted: Agree that the fact that there is no practical difference means that no change can be justified.
Proposed resolution:
In 26.5.3.2 [rand.eng.mers]:
Insert at the end of para 2.:
[Note: The lower r bits of Xi-n do not influence the state transition and hence should not be compared when comparing two mersenne_twister_engine objects. -- end note]In para 5. change:
The textual representation of xi consists of the values of Xi-n bitand ((2w - 1) - (2r - 1)), Xi-(n-1), ..., Xi-1, in that order.
Section: 26.5.7.1 [rand.util.seedseq] Status: NAD Editorial Submitter: Stephan Tolksdorf Opened: 2008-02-18 Last modified: 2009-03-09
View all other issues in [rand.util.seedseq].
View all issues with NAD Editorial status.
Discussion:
The for-loop in the algorithm specification has n iterations, where n is defined to be end - begin, i.e. the number of supplied w-bit quantities. Previous versions of this algorithm and the general logic behind it suggest that this is an oversight and that in the context of the for-loop n should be the number of full 32-bit quantities in b (rounded upwards). If w is 64, the current algorithm throws away half of all bits in b. If w is 16, the current algorithm sets half of all elements in v to 0.
There are two more minor issues:
[ Bellevue: ]
Move to OPEN Bill will try to propose a resolution by the next meeting.
[ post Bellevue: Bill provided wording. ]
This issue is made moot if 803 is accepted.
Proposed resolution:
Replace 26.5.7.1 [rand.util.seedseq] paragraph 6 with:
Effects: Constructs a seed_seq object by effectively concatenating the low-order u bits of each of the elements of the supplied sequence [begin, end) in ascending order of significance to make a (possibly very large) unsigned binary number b having a total of n bits, and then carrying out the following algorithm:
for( v.clear(); n > 0; n -= 32 ) v.push_back(b mod 232), b /= 232;
Rationale:
Addressed by N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X".Section: 26.5.5 [rand.predef] Status: NAD Submitter: P.J. Plauger Opened: 2008-02-20 Last modified: 2008-03-17
View all other issues in [rand.predef].
View all issues with NAD status.
Discussion:
The 10,000th value returned by knuth_b is supposed to be 1112339016. We get 2126698284.
Proposed resolution:
Change 26.5.5 [rand.predef]/p8:
typedef shuffle_order_engine<minstd_rand0, 256> knuth_b;Required behavior: The 10000th consecutive invocation of a default-constructed object of type knuth_b shall produce the value11123390162126698284.
[ Bellevue: Submitter withdraws defect. "We got the wrong value for entirely the right reasons". NAD. ]
Section: 26.5.7.1 [rand.util.seedseq] Status: NAD Editorial Submitter: Charles Karney Opened: 2008-02-22 Last modified: 2009-03-09
View all other issues in [rand.util.seedseq].
View all issues with NAD Editorial status.
Discussion:
seed_seq(InputIterator begin, InputIterator end); constructs a seed_seq object repacking the bits of supplied sequence [begin, end) into a 32-bit vector.
This repacking triggers several problems:
I propose simplifying this seed_seq constructor to be "32-bit only". Despite it's being simpler, there is NO loss of functionality (see below).
Here's how the description would read
26.5.7.1 [rand.util.seedseq] Class seed_seq
template<class InputIterator> seed_seq(InputIterator begin, InputIterator end);5 Requires: NO CHANGE
6 Effects: Constructs a seed_seq object by
for (InputIterator s = begin; s != end; ++s) v.push_back((*s) mod 2^32);
Discussion:
The chief virtues here are simplicity, portability, and generality.
Arguments (and counter-arguments) against making this change (and retaining the n2461 behavior) are:
The user can pass an array of unsigned char and seed_seq will nicely repack it.
Response: So what? Consider the seed string "ABC". The n2461 proposal results in
v = { 0x3, 0x434241 };
while the simplified proposal yields
v = { 0x41, 0x42, 0x43 };
The results produced by seed_seq::generate with the two inputs are different but nevertheless equivalently "mixed up" and this remains true even if the seed string is long.
With long strings (e.g., with bit-length comparable to the number of bits in the state), v is longer (by a factor of 4) with the simplified proposal and seed_seq::generate will be slower.
Response: It's unlikely that the efficiency of seed_seq::generate will be a big issue. If it is, the user is free to repack the seed vector before constructing seed_seq.
A user can pass an array of 64-bit integers and all the bits will be used.
Response: Indeed. However, there are many instances in the n2461 where integers are silently coerced to a narrower width and this should just be a case of the user needing to read the documentation. The user can of course get equivalent behavior by repacking his seed into 32-bit pieces. Furthermore, the unportability of the n2461 proposal with
unsigned long s[] = {1, 2, 3, 4};
seed_seq q(s, s+4);
which typically results in v = {1, 2, 3, 4} on 32-bit machines and in v = {1, 0, 2, 0, 3, 0, 4, 0} on 64-bit machines is a major pitfall for unsuspecting users.
Note: this proposal renders moot issues 782 and 800.
[ Bellevue: ]
Walter needs to ask Fermilab for guidance. Defer till tomorrow. Bill likes the proposed resolution.
[ Sophia Antipolis: ]
Marc Paterno wants portable behavior between 32bit and 64bit machines; we've gone to significant trouble to support portability of engines and their values.
Jens: the new algorithm looks perfectly portable
Marc Paterno to review off-line.
Modify the proposed resolution to read "Constructs a seed_seq object by the following algorithm ..."
Disposition: move to review; unanimous consent.
Proposed resolution:
Change 26.5.7.1 [rand.util.seedseq]:
template<class InputIterator, size_t u = numeric_limits<iterator_traits<InputIterator>::value_type>::digits> seed_seq(InputIterator begin, InputIterator end);-5- Requires: InputIterator shall satisfy the requirements of an input iterator (24.1.1) such that iterator_traits<InputIterator>::value_type shall denote an integral type.
-6- Constructs a seed_seq object by the following algorithm
rearranging some or all of the bits of the supplied sequence [begin,end) of w-bit quantities into 32-bit units, as if by the following:
First extract the rightmost u bits from each of the n = end - begin elements of the supplied sequence and concatenate all the extracted bits to initialize a single (possibly very large) unsigned binary number, b = ∑n-1i=0 (begin[i] mod 2u) · 2w·i (in which the bits of each begin[i] are treated as denoting an unsigned quantity). Then carry out the following algorithm:v.clear(); if ($w$ < 32) v.push_back($n$); for( ; $n$ > 0; --$n$) v.push_back(b mod 232), b /= 232;for (InputIterator s = begin; s != end; ++s) v.push_back((*s) mod 232);
Rationale:
Addressed by N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X".Section: 25.4.1 [alg.sort] Status: NAD Editorial Submitter: Paul McKenney Opened: 2008-02-27 Last modified: 2008-09-17
View all issues with NAD Editorial status.
Discussion:
Multi-threading is a good thing, but unsolicited multi-threading can potentially be harmful. For example, sort() performance might be greatly increased via a multithreaded implementation. However, such a multithreaded implementation could result in concurrent invocations of the user-supplied comparator. This would in turn result in problems given a caching comparator that might be written for complex sort keys. Please note that this is not a theoretical issue, as multithreaded implementations of sort() already exist.
Having a multithreaded sort() available is good, but it should not be the default for programs that are not explicitly multithreaded. Users should not be forced to deal with concurrency unless they have asked for it.
[ This may be covered by N2410 Thread-Safety in the Standard Library (Rev 1). ]
Proposed resolution:
Rationale:
This is already covered by 17.6.5.6/20 in N2723.Section: 19.5.2.1 [syserr.errcode.overview], 20.8.12.2.8 [util.smartptr.shared.io], 22.4.8 [facets.examples], 20.3.7.3 [bitset.operators], 26.4.6 [complex.ops], 27.6 [stream.buffers], 28.9 [re.submatch] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2008-04-10 Last modified: 2009-07-13
View all issues with NAD Editorial status.
Discussion:
Should the following use rvalues references to stream in insert/extract operators?
[ Sophia Antipolis ]
Agree with the idea in the issue, Alisdair to provide wording.
[ Daniel adds 2009-02-14: ]
The proposal given in the paper N2831 apparently resolves this issue.
[ Batavia (2009-05): ]
The cited paper is an earlier version of N2844, which changed the rvalue reference binding rules. That paper includes generic templates operator<< and operator>> that adapt rvalue streams.
We therefore agree with Daniel's observation. Move to NAD Editorial.
Proposed resolution:
Section: 22.4.2.2 [locale.nm.put] Status: NAD Submitter: Peter Dimov Opened: 2008-04-07 Last modified: 2008-06-18
View all issues with NAD status.
Discussion:
In the spirit of printf vs iostream...
POSIX printf says that %'d should insert grouping characters (and the implication is that in the absence of ' no grouping characters are inserted). The num_put facet, on the other hand, seems to always insert grouping characters. Can this be considered a defect worth fixing for C++0x? Maybe ios_base needs an additional flag?
[ Pablo Halpern: ]
I'm not sure it constitutes a defect, but I would be in favor of adding another flag (and corresponding manipulator).
[ Martin Sebor: ]
I don't know if it qualifies as a defect but I agree that there should be an easy way to control whether the thousands separator should or shouldn't be inserted. A new flag would be in line with the current design of iostreams (like boolalpha, showpos, or showbase).
[ Sophia Antipolis: ]
This is not a part of C99. LWG suggests submitting a paper may be appropriate.
Proposed resolution:
Section: 21.2 [char.traits] Status: NAD Editorial Submitter: Dietmar Kühl Opened: 2008-04-23 Last modified: 2009-07-13
View all other issues in [char.traits].
View all issues with NAD Editorial status.
Discussion:
Paragraph 4 of 21.2 [char.traits] mentions that this
section specifies two specializations (char_traits<char>
and (char_traits<wchar_t>). However, there are actually
four specializations provided, i.e. in addition to the two above also
char_traits<char16_t> and char_traits<char32_t>).
I guess this was just an oversight and there is nothing wrong with just
fixing this.
[ Alisdair adds: ]
char_traits< char16/32_t > should also be added to <ios_fwd> in 27.3 [iostream.forward], and all the specializations taking a char_traits parameter in that header.
[ Sophia Antipolis: ]
Idea of the issue is ok.
Alisdair to provide wording, once that wording arrives, move to review.
[ 2009-05-04 Alisdair adds: ]
The main point of the issue was resolved editorially in N2723, so we are close to NAD Editorial. However, exploring the issue we found a second tweak was necessary for <iosfwd> and that is still outstanding, so here are the words I am long overdue delivering:
[ Howard: I've put Alisdair's words into the proposed wording section and moved the issue to Review. ]
[ Original proposed wording. ]
Replace paragraph 4 of 21.2 [char.traits] by:
This subclause specifies a struct template,
char_traits<charT>, and four explicit specializations of it,char_traits<char>,char_traits<char16_t>,char_traits<char32_t>, andchar_traits<wchar_t>, all of which appear in the header <string> and satisfy the requirements below.
[ Batavia (2009-05): ]
We agree. Move to NAD Editorial.
Proposed resolution:
Change Forward declarations 27.3 [iostream.forward]:
Header <iosfwd> synopsis
namespace std { template<class charT> class char_traits; template<> class char_traits<char>; template<> class char_traits<char16_t>; template<> class char_traits<char32_t>; template<> class char_traits<wchar_t>; ... }
Section: 21.2.3 [char.traits.specializations] Status: NAD Editorial Submitter: Dietmar Kühl Opened: 2008-04-23 Last modified: 2008-06-19
View all other issues in [char.traits.specializations].
View all issues with NAD Editorial status.
Discussion:
In Table 56 (Traits requirements) the not_eof() member function
is using an argument of type e which denotes an object of
type X::int_type. However, the specializations in
21.2.3 [char.traits.specializations] all use char_type.
This would effectively mean that the argument type actually can't
represent EOF in the first place. I'm pretty sure that the type used
to be int_type which is quite obviously the only sensible
argument.
This issue is close to being editorial. I suspect that the proposal
changing this section to include the specializations for char16_t
and char32_t accidentally used the wrong type.
Proposed resolution:
In 21.2.3.1 [char.traits.specializations.char],
21.2.3.2 [char.traits.specializations.char16_t],
21.2.3.3 [char.traits.specializations.char32_t], and
[char.traits.specializations.wchar_t] correct the
argument type from char_type to int_type.
Rationale:
Already fixed in WP.Section: 19.5 [syserr] Status: NAD Submitter: Beman Dawes Opened: 2008-05-14 Last modified: 2008-09-17
View all other issues in [syserr].
View all issues with NAD status.
Discussion:
Initialization of objects of class error_code (19.5.2 [syserr.errcode]) and class error_condition (19.5.3 [syserr.errcondition]) can be made simpler and more reliable by use of the new constexpr feature [N2349] of C++0x. Less code will need to be generated for both library implementations and user programs when manipulating constant objects of these types.
This was not proposed originally because the constant expressions proposal was moving into the standard at about the same time as the Diagnostics Enhancements proposal [N2241], and it wasn't desirable to make the later depend on the former. There were also technical concerns as to how constexpr would apply to references. Those concerns are now resolved; constexpr can't be used for references, and that fact is reflected in the proposed resolution.
Thanks to Jens Maurer, Gabriel Dos Reis, and Bjarne Stroustrup for clarification of constexpr requirements.
LWG issue 804 is related in that it raises the question of whether the exposition only member cat_ of class error_code (19.5.2 [syserr.errcode]) and class error_condition (19.5.3 [syserr.errcondition]) should be presented as a reference or pointer. While in the context of 804 that is arguably an editorial question, presenting it as a pointer becomes more or less required with this proposal, given constexpr does not play well with references. The proposed resolution thus changes the private member to a pointer, which also brings it in sync with real implementations.
[ Sophia Antipolis: ]
On going question of extern pointer vs. inline functions for interface.
[ Pre-San Francisco: ]
Beman Dawes reports that this proposal is unimplementable, and thus NAD.
Implementation would require constexpr objects of classes derived from class error_category, which has virtual functions, and that is not allowed by the core language. This was determined when trying to implement the proposal using a constexpr enabled compiler provided by Gabriel Dos Reis, and subsequently verified in discussions with Gabriel and Jens Maurer.
Proposed resolution:
The proposed wording assumes the LWG 805 proposed wording has been applied to the WP, resulting in the former posix_category being renamed generic_category. If 805 has not been applied, the names in this proposal must be adjusted accordingly.
Change 19.5.1.1 [syserr.errcat.overview] Class error_category overview error_category synopsis as indicated:
const error_category& get_generic_category();const error_category& get_system_category();staticextern const error_category&* const generic_category= get_generic_category();staticextern const error_category&* constnative_categorysystem_category= get_system_category();
Change 19.5.1.5 [syserr.errcat.objects] Error category objects as indicated:
extern const error_category&* constget_generic_category();
Returns: A referencegeneric_category shall point toana statically initialized object of a type derived from class error_category.
Remarks:The object's default_error_condition and equivalent virtual functions shall behave as specified for the class error_category. The object's name virtual function shall return a pointer to the string "GENERIC".extern const error_category&* constget_system_category();
Returns: A referencesystem_category shall point toana statically initialized object of a type derived from class error_category.
Remarks:The object's equivalent virtual functions shall behave as specified for class error_category. The object's name virtual function shall return a pointer to the string "system". The object's default_error_condition virtual function shall behave as follows:If the argument ev corresponds to a POSIX errno value posv, the function shall return error_condition(posv, generic_category). Otherwise, the function shall return error_condition(ev, system_category). What constitutes correspondence for any given operating system is unspecified. [Note: The number of potential system error codes is large and unbounded, and some may not correspond to any POSIX errno value. Thus implementations are given latitude in determining correspondence. -- end note]
Change 19.5.2.1 [syserr.errcode.overview] Class error_code overview as indicated:
class error_code {
public:
...;
constexpr error_code(int val, const error_category&* cat);
...
void assign(int val, const error_category&* cat);
...
const error_category&* category() const;
...
private:
int val_; // exposition only
const error_category&* cat_; // exposition only
Change 19.5.2.2 [syserr.errcode.constructors] Class error_code constructors as indicated:
constexpr error_code(int val, const error_category&* cat);Effects: Constructs an object of type error_code.
Postconditions: val_ == val and cat_ == cat.
Throws: Nothing.
Change 19.5.2.3 [syserr.errcode.modifiers] Class error_code modifiers as indicated:
void assign(int val, const error_category&* cat);Postconditions: val_ == val and cat_ == cat.
Throws: Nothing.
Change 19.5.2.4 [syserr.errcode.observers] Class error_code observers as indicated:
const error_category&* category() const;Returns: cat_.
Throws: Nothing.
Change 19.5.3.1 [syserr.errcondition.overview] Class error_condition overview as indicated:
class error_condition {
public:
...;
constexpr error_condition(int val, const error_category&* cat);
...
void assign(int val, const error_category&* cat);
...
const error_category&* category() const;
...
private:
int val_; // exposition only
const error_category&* cat_; // exposition only
Change 19.5.3.2 [syserr.errcondition.constructors] Class error_condition constructors as indicated:
constexpr error_condition(int val, const error_category&* cat);Effects: Constructs an object of type error_condition.
Postconditions: val_ == val and cat_ == cat.
Throws: Nothing.
Change 19.5.3.3 [syserr.errcondition.modifiers] Class error_condition modifiers as indicated:
void assign(int val, const error_category&* cat);Postconditions: val_ == val and cat_ == cat.
Throws: Nothing.
Change 19.5.3.4 [syserr.errcondition.observers] Class error_condition observers as indicated:
const error_category&* category() const;Returns: cat_.
Throws: Nothing.
Throughout 19.5 [syserr] System error support, change "category()." to "category()->". Appears approximately six times.
[Partially Editorial] In 19.5.4 [syserr.compare] Comparison operators, paragraphs 2 and 4, change "category.equivalent(" to "category()->equivalent(".
Change 19.5.5.1 [syserr.syserr.overview] Class system_error overview as indicated:
public: system_error(error_code ec, const string& what_arg); system_error(error_code ec); system_error(int ev, const error_category&* ecat, const string& what_arg); system_error(int ev, const error_category&* ecat);
Change 19.5.5.2 [syserr.syserr.members] Class system_error members as indicated:
system_error(int ev, const error_category&* ecat, const string& what_arg);Effects: Constructs an object of class system_error.
Postconditions: code() == error_code(ev, ecat) and strcmp(runtime_error::what(), what_arg.c_str()) == 0.
system_error(int ev, const error_category&* ecat);Effects: Constructs an object of class system_error.
Postconditions: code() == error_code(ev, ecat) and strcmp(runtime_error::what(), "") == 0.
Rationale:
[ San Francisco: ]
NAD because Beman said so.
Section: 17.6.1.3 [compliance] Status: NAD Submitter: Beman Dawes Opened: 2008-05-14 Last modified: 2009-07-16
View all other issues in [compliance].
View all issues with NAD status.
Discussion:
Once the C++0x standard library is feature complete, the LWG needs to review 17.6.1.3 [compliance] Freestanding implementations header list to ensure it reflects LWG consensus.
[ San Francisco: ]
This is a placeholder defect to remind us to review the table once we've stopped adding headers to the library.
Three new headers that need to be added to the list:
<initializer_list> <concept> <iterator_concepts><iterator_concepts>, in particular, has lots of stuff that isn't needed, so maybe the stuff that is needed should be broken out into a separate header.
Robert: What about reference_closure? It's currently in <functional>.
[ Post Summit Daniel adds: ]
- The comment regarding reference_closure seems moot since it was just recently decided to remove that.
- A reference to proposal N2814 ("Fixing freestanding") should be added. This paper e.g. proposes to add only <initializer_list> to the include list of freestanding.
[ 2009-07 Frankfurt: ]
Addressed by paper N2814.
Move to NAD.
Proposed resolution:
basic_ios::copyfmt() overly loosely specified
Section: 27.5.4.2 [basic.ios.members] Status: NAD Editorial Submitter: Martin Sebor Opened: 2008-05-17 Last modified: 2009-07-13
View other active issues in [basic.ios.members].
View all other issues in [basic.ios.members].
View all issues with NAD Editorial status.
Discussion:
The basic_ios::copyfmt() member function is specified in 27.5.4.2 [basic.ios.members] to have the following effects:
Effects: If(this == &rhs)does nothing. Otherwise assigns to the member objects of*thisthe corresponding member objects ofrhs, except that
rdstate()andrdbuf()are left unchanged;exceptions()is altered last by callingexceptions(rhs.except)- the contents of arrays pointed at by
pwordandiwordare copied not the pointers themselves
Since the rest of the text doesn't specify what the member objects
of basic_ios are this seems a little too loose.
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to NAD Editorial.
Proposed resolution:
I propose to tighten things up by adding a Postcondition clause to the function like so:
Postconditions:
copyfmt()postconditionsElement Value rdbuf()unchanged tie()rhs.tie()rdstate()unchanged exceptions()rhs.exceptions()flags()rhs.flags()width()rhs.width()precision()rhs.precision()fill()rhs.fill()getloc()rhs.getloc()
The format of the table follows Table 117 (as
of N2588): basic_ios::init()
effects.
The intent of the new table is not to impose any new requirements or change existing ones, just to be more explicit about what I believe is already there.
Section: 23.4 [associative], 23.5 [unord] Status: NAD Future Submitter: Alan Talbot Opened: 2008-05-18 Last modified: 2009-09-20
View all other issues in [associative].
View all issues with NAD Future status.
Discussion:
Splice is a very useful feature of list. This functionality is also very useful for any other node based container, and I frequently wish it were available for maps and sets. It seems like an omission that these containers lack this capability. Although the complexity for a splice is the same as for an insert, the actual time can be much less since the objects need not be reallocated and copied. When the element objects are heavy and the compare operations are fast (say a map<int, huge_thingy>) this can be a big win.
Suggested resolution:
Add the following signatures to map, set, multimap, multiset, and the unordered associative containers:
void splice(list<T,Allocator>&& x); void splice(list<T,Allocator>&& x, const_iterator i); void splice(list<T,Allocator>&& x, const_iterator first, const_iterator last);
Hint versions of these are also useful to the extent hint is useful. (I'm looking for guidance about whether hints are in fact useful.)
void splice(const_iterator position, list<T,Allocator>&& x); void splice(const_iterator position, list<T,Allocator>&& x, const_iterator i); void splice(const_iterator position, list<T,Allocator>&& x, const_iterator first, const_iterator last);
[ Sophia Antipolis: ]
Don't try to splice "list" into the other containers, it should be container-type.
forward_list already has splice_after.
Would "splice" make sense for an unordered_map?
Jens, Robert: "splice" is not the right term, it implies maintaining ordering in lists.
Howard: adopt?
Jens: absorb?
Alan: subsume?
Robert: recycle?
Howard: transfer? (but no direction)
Jens: transfer_from. No.
Alisdair: Can we give a nothrow guarantee? If your compare() and hash() doesn't throw, yes.
Daniel: For unordered_map, we can't guarantee nothrow.
[ San Francisco: ]
Martin: this would possibly outlaw an implementation technique that is currently in use; caching nodes in containers.
Alan: if you cache in the allocator, rather than the individual container, this proposal doesn't interfere with that.
Martin: I'm not opposed to this, but I'd like to see an implementation that demonstrates that it works.
[ 2009-07 Frankfurt: ]
NAD Future.
[ 2009-09-19 Howard adds: ]
I'm not disagreeing with the NAD Future resolution. But when the future gets here, here is a possibility worth exploring:
Add to the "unique" associative containers:
typedef details node_ptr; node_ptr remove(const_iterator p); pair<iterator, bool> insert(node_ptr&& nd); iterator insert(const_iterator p, node_ptr&& nd);And add to the "multi" associative containers:
typedef details node_ptr; node_ptr remove(const_iterator p); iterator insert(node_ptr&& nd); iterator insert(const_iterator p, node_ptr&& nd);Container::node_ptr is a smart pointer much like unique_ptr. It owns a node obtained from the container it was removed from. It maintains a reference to the allocator in the container so that it can properly deallocate the node if asked to, even if the allocator is stateful. This being said, the node_ptr can not outlive the container for this reason.
The node_ptr offers "const-free" access to the node's value_type.
With this interface, clients have a great deal of flexibility:
- A client can remove a node from one container, and insert it into another (without any heap allocation). This is the splice functionality this issue asks for.
- A client can remove a node from a container, change its key or value, and insert it back into the same container, or another container, all without the cost of allocating a node.
- If the Compare function is nothrow (which is very common), then this functionality is nothrow unless modifying the value throws. And if this does throw, it does so outside of the containers involved.
- If the Compare function does throw, the insert function will have the argument nd retain ownership of the node.
- The node_ptr should be independent of the Compare parameter so that a node can be transferred from set<T, C1, A> to set<T, C2, A> (for example).
Here is how the customer might use this functionality:
Splice a node from one container to another:
m2.insert(m1.remove(i));Change the "key" in a std::map without the cost of node reallocation:
auto p = m.remove(i); p->first = new_key; m.insert(std::move(p));Change the "value" in a std::set without the cost of node reallocation:
auto p = s.remove(i); *p = new_value; s.insert(std::move(p));Move a move-only or heavy object out of an associative container (as opposed to the proposal in 1041):
MoveOnly x = std::move(*s.remove(i));
- remove(i) transfers ownership of the node from the set to a temporary node_ptr.
- The node_ptr is dereferenced, and that non-const reference is sent to move to cast it to an rvalue.
- The rvalue MoveOnly is move constructed into x from the node_ptr.
- ~node_ptr() destructs the moved-from MoveOnly and deallocates the node.
Contrast this with the 1041 solution:
MoveOnly x = std::move(s.extract(i).first);The former requires one move construction for x while the latter requires two (one into the pair and then one into x). Either of these constructions can throw (say if there is only a copy constructor for x). With the former, the point of throw is outside of the container s, after the element has been removed from the container. With the latter, one throwing construction takes place prior to the removal of the element, and the second takes place after the element is removed.
The "node insertion" API maintains the API associated with inserting value_types so the customer can use familiar techniques for getting an iterator to the inserted node, or finding out whether it was inserted or not for the "unique" containers.
Lightly prototyped. No implementation problems. Appears to work great for the client.
Proposed resolution:
Section: 20.3.3 [pairs] Status: NAD Submitter: Thorsten Ottosen Opened: 2008-05-23 Last modified: 2008-06-18
View other active issues in [pairs].
View all other issues in [pairs].
View all issues with NAD status.
Discussion:
I have one issue with std::pair. Well, it might just be a very annoying historical accident, but why is there no default template argument for the second template argument? This is so annoying when the type in question is looong and hard to write (type deduction with auto won't help those cases where we use it as a return or argument type).
Proposed resolution:
Change the synopsis in 20.3 [utility] to read:
template <class T1, class T2 = T1> struct pair;
Change 20.3.3 [pairs] to read:
namespace std {
template <class T1, class T2 = T1>
struct pair {
typedef T1 first_type;
typedef T2 second_type;
...
Rationale:
std::pair is a heterogeneous container.Section: 18.4.1 [cstdint.syn] Status: NAD Editorial Submitter: Martin Sebor Opened: 2008-05-17 Last modified: 2008-09-17
View all other issues in [cstdint.syn].
View all issues with NAD Editorial status.
Discussion:
In specifying the names of macros and types defined in
header <stdint.h>, C99 makes use of the
symbol N to accommodate unusual platforms with
word sizes that aren't powers of two. C99
permits N to take on any positive integer value
(including, for example, 24).
In cstdint.syn Header <cstdint>
synopsis, C++ on the other hand, fixes the value
of N to 8, 16, 32, and 64, and specifies only
types with these exact widths.
In addition, paragraph 1 of the same section makes use of a rather informal shorthand notation to specify sets of macros. When interpreted strictly, the notation specifies macros such as
INT_8_MIN that are not intended to be specified.
Finally, the section is missing the usual table of symbols defined in that header, making it inconsistent with the rest of the specification.
Proposed resolution:
I propose to use the same approach in the C++ spec as C99 uses, that
is, to specify the header synopsis in terms of "exposition only" types
that make use of the symbol N to denote one or
more of a theoretically unbounded set of widths.
Further, I propose to add a new table to section listing the symbols defined in the header using a more formal notation that avoids introducing inconsistencies.
To this effect, in cstdint.syn
Header <cstdint> synopsis, replace both the
synopsis and paragraph 1 with the following text:
- In the names defined in the
<cstdint>header, the symbolNrepresents a positive decimal integer with no leading zeros (e.g., 8 or 24, but not 0, 04, or 048). With the exception of exact-width types, macros and types for values ofNin the set of 8, 16, 32, and 64 are required. Exact-width types, and any macros and types for values ofNother than 8, 16, 32, and 64 are optional. However, if an implementation provides integer types with widths of 8, 16, 32, or 64 bits, the corresponding exact-width types and macros are required.namespace std { // required types // Fastest minimum-width integer types typedef signed integer type int_fast8_t; typedef signed integer type int_fast16_t; typedef signed integer type int_fast32_t; typedef signed integer type int_fast64_t; typedef unsigned integer type uint_fast8_t; typedef unsigned integer type uint_fast16_t; typedef unsigned integer type uint_fast32_t; typedef unsigned integer type uint_fast64_t; // Minimum-width integer types typedef signed integer type int_least8_t; typedef signed integer type int_least16_t; typedef signed integer type int_least32_t; typedef signed integer type int_least64_t; typedef unsigned integer type uint_least8_t; typedef unsigned integer type uint_least16_t; typedef unsigned integer type uint_least32_t; typedef unsigned integer type uint_least64_t; // Greatest-width integer types typedef signed integer type intmax_t; typedef unsigned integer type uintmax_t; // optionally defined types // Exact-width integer types typedef signed integer type intN_t; typedef unsigned integer type uintN_t; // Fastest minimum-width integer types for values // of N other than 8, 16, 32, and 64 typedef signed integer type uint_fastN_t; typedef unsigned integer type uint_fastN_t; // Minimum-width integer types for values // of N other than 8, 16, 32, and 64 typedef signed integer type uint_leastN_t; typedef unsigned integer type uint_leastN_t; // Integer types capable of holding object pointers typedef signed integer type intptr_t; typedef signed integer type intptr_t; }
[Note to editor: Remove all of the existing paragraph 1 from cstdint.syn.]
Table ??: Header<cstdint>synopsis
Type Name(s) Macros: INTN_MIN INTN_MAX UINTN_MAX INT_FASTN_MIN INT_FASTN_MAX UINT_FASTN_MAX INT_LEASTN_MIN INT_LEASTN_MAX UINT_LEASTN_MAX INTPTR_MIN INTPTR_MAX UINTPTR_MAX INTMAX_MIN INTMAX_MAX UINTMAX_MAX PTRDIFF_MIN PTRDIFF_MAX PTRDIFF_MAX SIG_ATOMIC_MIN SIG_ATOMIC_MAX SIZE_MAX WCHAR_MIN WCHAR_MAX WINT_MIN WINT_MAX INTN_C() UINTN_C() INTMAX_C() UINTMAX_C() Types: intN_t uintN_t int_fastN_t uint_fastN_t int_leastN_t uint_leastN_t intptr_t uintptr_t intmax_t uintmax_t
Section: 20.6.7 [meta.trans.other] Status: NAD Submitter: Thorsten Ottosen Opened: 2008-06-05 Last modified: 2008-09-16
View other active issues in [meta.trans.other].
View all other issues in [meta.trans.other].
View all issues with NAD status.
Discussion:
The type traits library contains various traits to dealt with polymorphic types, e.g. std::has_virtual_destructor, std::is_polymorphic and std::is_base_of. However, there is no way to compute the unique public base class of a type if such one exists. Such a trait could be very useful if one needs to instantiate a specialization made for the root class whenever a derived class is passed as parameter. For example, imagine that you wanted to specialize std::hash for a class hierarchy---instead of specializing each class, you could specialize the std::hash<root_class> and provide a partial specialization that worked for all derived classes.
This ability---to specify operations in terms of their equivalent in the root class---can be done with e.g. normal functions, but there is, AFAIK, no way to do it for class templates. Being able to access compile-time information about the type-hierachy can be very powerful, and I therefore also suggest traits that computes the directly derived class whenever that is possible.
If the computation can not be done, the traits should fall back on an identity transformation. I expect this gives the best overall usability.
Proposed resolution:
Add the following to the synopsis in 20.6.2 [meta.type.synop] under "other transformations":
template< class T > struct direct_base_class; template< class T > struct direct_derived_class; template< class T > struct root_base_class;
Add three new entries to table 51 (20.6.7 [meta.trans.other]) with the following content
Template Condition Comments template< class T > struct direct_base_class; T shall be a complete type. The member typedef type shall equal the accessible unambiguous direct base class of T. If no such type exists, the member typedef type shall equal T. template< class T > struct direct_derived_class; T shall be a complete type. The member typedef type shall equal the unambiguous type which has T as an accessible unambiguous direct base class. If no such type exists, the member typedef type shall equal T. template< class T > struct root_base_class; T shall be a complete type. The member typedef type shall equal the accessible unambiguous most indirect base class of T. If no such type exists, the member typedef type shall equal T.
Rationale:
2008-9-16 San Francisco: Issue pulled by author prior to being reviewed by the LWG.Section: 23.3.2.2 [deque.capacity] Status: NAD Submitter: Hervé Brönnimann Opened: 2008-06-11 Last modified: 2008-09-22
View all other issues in [deque.capacity].
View all issues with NAD status.
Discussion:
The main point is that capacity can be viewed as a mechanism to guarantee the validity of iterators when only push_back/pop_back operations are used. For vector, this goes with reallocation. For deque, this is a bit more subtle: capacity() of a deque may shrink, whereas that of vector doesn't. In a circular buffer impl. of the map, as Howard did, there is very similar notion of capacity: as long as size() is less than B * (total size of the map - 2), it is guaranteed that no iterator is invalidated after any number of push_front/back and pop_front/back operations. But this does not hold for other implementations.
Still, I believe, capacity() can be defined by size() + how many push_front/back minus pop_front/back that can be performed before terators are invalidated. In a classical impl., capacity() = size() + the min distance to either "physical" end of the deque (i.e., counting the empty space in the last block plus all the blocks until the end of the map of block pointers). In Howard's circular buffer impl., capacity() = B * (total size of the map - 2) still works with this definition, even though the guarantee could be made stronger.
A simple picture of a deque:
A-----|----|-----|---F+|++++|++B--|-----|-----Z
(A,Z mark the beginning/end, | the block boundaries, F=front, B=back, and - are uninitialized, + are initialized) In that picture: capacity = size() + min(dist(A,F),dist(B,Z)) = min (dist(A,B),dist(F,Z)).
Reserve(n) can grow the map of pointers and add possibly a number of empty blocks to it, in order to guarantee that the next n-size() push_back/push_front operations will not invalidate iterators, and also will not allocate (i.e. cannot throw). The second guarantee is not essential and can be left as a QoI. I know well enough existing implementations of deque (sgi/stl, roguewave, stlport, and dinkumware) to know that either can be implemented with no change to the existing class layout and code, and only a few modifications if blocks are pre-allocated (instead of always allocating a new block, check if the next entry in the map of block pointers is not zero).
Due to the difference with vector, wording is crucial. Here's a proposed wording to make things concrete; I tried to be reasonably careful but please double-check me:
[ San Francisco: ]
Hans: should the Returns clause for capacity read "1 Returns: A lower bound..." rather than "1 Returns: An upper bound..."
Howard: maybe what's needed is capacity_front and capacity_back. In fact, I think I implemented a deque that had these members as implementation details.
Proposed resolution:
Add new signatures to synopsis in 23.3.2 [deque]:
size_type capacity() const; bool reserve(size_type n);
Add new signatures to 23.3.2.2 [deque.capacity]:
size_type capacity() const;1 Returns: An upper bound on n + max(n_f - m_f, n_b - m_b) such that, for any sequence of n_f push_front, m_f pop_front, n_b push_back, and m_b pop_back operations, interleaved in any order, starting with the current deque of size n, the deque does not invalidate any of its iterators except to the erased elements.
2 Remarks: Unlike a vector's capacity, the capacity of a deque can decrease after a sequence of insertions at both ends, even if none of the operations caused the deque to invalidate any of its iterators except to the erased elements.
bool reserve(size_type n);2 Effects: A directive that informs a deque of a planned sequence of push_front, pop_front, push_back, and pop_back operations, so that it can manage iterator invalidation accordingly. After reserve(), capacity() is greater or equal to the argument of reserve if this operation returns true; and equal to the previous value of capacity() otherwise. If an exception is thrown, there are no effects.
3 Returns: true if iterators are invalidated as a result of this operation, and false otherwise.
4 Complexity: It does not change the size of the sequence and takes at most linear time in n.
5 Throws: length_error if n > max_size().
6 Remarks: It is guaranteed that no invalidation takes place during a sequence of insert or erase operations at either end that happens after a call to reserve() except to the erased elements, until the time when an insertion would make max(n_f-m_f, n_b-m_b) larger than capacity(), where n_f is the number of push_front, m_f of pop_front, n_b of push_back, and m_b of pop_back operations since the call to reserve().
7 An implementation is free to pre-allocate buffers so as to offer the additional guarantee that no exception will be thrown during such a sequence other than by the element constructors.
And 23.3.2.3 [deque.modifiers] para 1, can be enhanced:
1 Effects: An insertion in the middle of the deque invalidates all the iterators and references to elements of the deque. An insertion at either end of the deque invalidates all the iterators to the deque, unless provisions have been made with reserve, but has no effect on the validity of references to elements of the deque.
Rationale:
Complication outweighs the benefit.Section: 25.4.5.1 [includes] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2008-07-02 Last modified: 2009-07-13
View all other issues in [includes].
View all issues with NAD Editorial status.
Discussion:
In 25.4.5.1 [includes] the complexity is "at most -1 comparisons" if passed two empty ranges. I don't know how to perform a negative number of comparisions!
This same issue also applies to:
[ 2009-03-30 Beman adds: ]
Suggest NAD. The complexity of empty ranges is -1 in other places in the standard. See 25.4.4 [alg.merge] merge and inplace_merge, and forward_list merge, for example. The time and effort to find and fix all places in the standard where empty range[s] result in negative complexity isn't worth the very limited benefit.
[ 2009-05-09 Alisdair adds: ]
I'm not happy with NAD if we can find a simple solution.
How about adding a rider somewhere in clause 17 suggesting that complexities that specify a negative number of operations are treated as specifying zero operations? That should generically solve the issue without looking for further cases.
[ Batavia (2009-05): ]
Pete to provide "straightforward" wording. Move to NAD Editorial.
Proposed resolution:
Recommend NAD.
Section: 27.9.1 [fstreams] Status: NAD Submitter: Steve Clamage Opened: 2008-07-08 Last modified: 2009-07-13
View all other issues in [fstreams].
View all issues with NAD status.
Discussion:
Suppose writing to an [o]fstream fails and you later close the stream. The overflow() function is called to flush the buffer (if it exists). Then the file is unconditionally closed, as if by calling flcose.
If either overflow or fclose fails, close() reports failure, and clearly the stream should be in a failed or bad state.
Suppose the buffer is empty or non-existent (so that overflow() does not fail), and fclose succeeds. The close() function reports success, but what is the state of the stream?
[ Batavia (2009-05): ]
Tom's impression is that the issue is about the failbit, etc.
Bill responds that the stream is now closed, and any status bits remain unchanged.
See the description of close() in 27.9.1.17 [fstream.members].
We prefer not to add wording to say that nothing changes. Move to NAD.
Proposed resolution:
Section: 29.6 [atomics.types.operations] Status: NAD Editorial Submitter: Anthony Williams Opened: 2008-07-10 Last modified: 2008-09-17
View other active issues in [atomics.types.operations].
View all other issues in [atomics.types.operations].
View all issues with NAD Editorial status.
Discussion:
There's an error in 29.6 [atomics.types.operations]/p9:
C atomic_load(const volatile A * object); C atomic_load_explicit(const volatile A * object, memory_order); C A ::load(memory_order order = memory_order_seq_cst) const volatile;Requires: The order argument shall not be memory_order_acquire nor memory_order_acq_rel.
I believe that this should state
shall not be memory_order_release.
There's also an error in 29.6 [atomics.types.operations]/p17:
... When only one memory_order argument is supplied, the value of success is order, and the value of failure is order except that a value of memory_order_acq_rel shall be replaced by the value memory_order_require ...
I believe this should state
shall be replaced by the value memory_order_acquire ...
Proposed resolution:
Change 29.6 [atomics.types.operations]/p9:
C atomic_load(const volatile A * object); C atomic_load_explicit(const volatile A * object, memory_order); C A ::load(memory_order order = memory_order_seq_cst) const volatile;Requires: The order argument shall not be
memory_order_acquirememory_order_release nor memory_order_acq_rel.
Change 29.6 [atomics.types.operations]/p17:
... When only one memory_order argument is supplied, the value of success is order, and the value of failure is order except that a value of memory_order_acq_rel shall be replaced by the valuememory_order_requirememory_order_acquire ...
Rationale:
Already fixed by the time the LWG processed it.Section: 26.6.2.1 [valarray.cons] Status: NAD Editorial Submitter: Alberto Ganesh Barbati Opened: 2008-07-20 Last modified: 2009-07-13
View other active issues in [valarray.cons].
View all other issues in [valarray.cons].
View all issues with NAD Editorial status.
Discussion:
From 26.6.2.1 [valarray.cons], paragraph 2:
explicit valarray(size_t);The array created by this constructor has a length equal to the value of the argument. The elements of the array are constructed using the default constructor for the instantiating type T.
The problem is that the most obvious Ts for valarray are float and double, they don't have a default constructor. I guess the intent is to value-initialize the elements, so I suggest replacing:
The elements of the array are constructed using the default constructor for the instantiating type T.
with
The elements of the array are value-initialized.
There is another reference to the default constructor of T in the non-normative note in paragraph 9. That reference should also be replaced. (The normative wording in paragraph 8 refers to T() and so it doesn't need changes).
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to NAD Editorial.
Proposed resolution:
Change 26.6.2.1 [valarray.cons], paragraph 2:
explicit valarray(size_t);The array created by this constructor has a length equal to the value of the argument. The elements of the array areconstructed using the default constructor for the instantiating type Tvalue-initialized (8.5 [dcl.init]).
Change 26.6.2.7 [valarray.members], paragraph 9:
[Example: If the argument has the value -2, the first two elements of the result will beconstructed using the default constructorvalue-initialized (8.5 [dcl.init]); the third element of the result will be assigned the value of the first element of the argument; etc. -- end example]
Section: 3.9.1 [basic.fundamental] Status: NAD Editorial Submitter: Travis Vitek Opened: 2008-06-30 Last modified: 2009-07-17
View all issues with NAD Editorial status.
Discussion:
Neither the term "signed integral type" nor the term "unsigned integral type" is defined in the core language section of the standard, therefore the library section should avoid its use. The terms signed integer type and unsigned integer type are indeed defined (in 3.9.1 [basic.fundamental]), thus the usages should be replaced accordingly.
Note that the key issue here is that "signed" + "integral type" !=
"signed integral type".
The types bool, char, char16_t,
char32_t and wchar_t are all listed as
integral types, but are neither of signed integer type or
unsigned integer type. According to 3.9 [basic.types] p7, a synonym for
integral type is integer type.
Given this, one may choose to assume that an integral type that
can represent values less than zero is a signed integral type.
Unfortunately this can cause ambiguities.
As an example, if T is unsigned char, the
expression make_signed<T>::type, is supposed to
name a signed integral type. There are potentially two types that
satisfy this requirement, namely signed char and
char (assuming CHAR_MIN < 0).
[ San Francisco: ]
Plum, Sebor to review.
[ Post Summit Daniel adds: ]
The proposed resolution needs to be "conceptualized". Currently we have in [concept.support] only concept IntegralType for all "integral types", thus indeed the current Container concept and Iterator concepts are sufficiently satisfied with "integral types". If the changes are applied, we might ask core for concept BilateralIntegerType and add proper restrictions to the library concepts.
Proposed resolution:
I propose to use the terms "signed integer type" and "unsigned integer type" in place of "signed integral type" and "unsigned integral type" to eliminate such ambiguities.
The proposed change makes it absolutely clear that the difference between two pointers cannot be char or wchar_t, but could be any of the signed integer types. 5.7 [expr.add] paragraph 6...
- When two pointers to elements of the same array object are subtracted, the result is the difference of the subscripts of the two array elements. The type of the result is an implementation-defined
signed integral typesigned integer type; this type shall be the same type that is defined asstd::ptrdiff_tin the<cstdint>header (18.1)...
The proposed change makes it clear that X::size_type and X::difference_type cannot be char or wchar_t, but could be one of the signed or unsigned integer types as appropriate. 20.2.2 [allocator.requirements] table 40...
Table 40: Allocator requirements
expression return type assertion/note/pre/post-condition X::size_type unsigned integral typeunsigned integer typea type that can represent the size of the largest object in the allocation model. X::difference_type signed integral typesigned integer typea type that can represent the difference between any two pointers in the allocation model.
The proposed change makes it clear that make_signed<T>::type must be one of the signed integer types as defined in 3.9.1. Ditto for make_unsigned<T>type and unsigned integer types. 20.6.6.3 [meta.trans.sign] table 48...
Table 48: Sign modifications
Template Comments template <class T> struct make_signed; If Tnames a (possibly cv-qualified)signed integral typesigned integer type (3.9.1) then the member typedeftypeshall name the typeT; otherwise, ifTnames a (possibly cv-qualified)unsigned integral typeunsigned integer type thentypeshall name the correspondingsigned integral typesigned integer type, with the same cv-qualifiers asT; otherwise,typeshall name thesigned integral typesigned integer type with the smallest rank (4.13) for whichsizeof(T) == sizeof(type), with the same cv-qualifiers asT. Requires:Tshall be a (possibly cv-qualified) integral type or enumeration but not abooltype.template <class T> struct make_unsigned; If Tnames a (possibly cv-qualified)unsigned integral typeunsigned integer type (3.9.1) then the member typedeftypeshall name the typeT; otherwise, ifTnames a (possibly cv-qualified)signed integral typesigned integer type thentypeshall name the correspondingunsigned integral typeunsigned integer type, with the same cv-qualifiers asT; otherwise,typeshall name theunsigned integral typeunsigned integer type with the smallest rank (4.13) for whichsizeof(T) == sizeof(type), with the same cv-qualifiers asT. Requires:Tshall be a (possibly cv-qualified) integral type or enumeration but not abooltype.
Note: I believe that the basefield values should probably be prefixed with ios_base:: as they are in 22.4.2.2.2 [facet.num.put.virtuals] The listed virtuals are all overloaded on signed and unsigned integer types, the new wording just maintains consistency. 22.4.2.1.2 [facet.num.get.virtuals] table 78...
Table 78: Integer Conversions
State stdio equivalent basefield == oct %o basefield == hex %X basefield == 0 %i signed integral typesigned integer type%d unsigned integral typeunsigned integer type%u
Rationale is same as above. 22.4.2.2.2 [facet.num.put.virtuals] table 80...
Table 80: Integer Conversions
State stdio equivalent basefield == ios_base::oct %o (basefield == ios_base::hex) && !uppercase %x (basefield == ios_base::hex) %X basefield == 0 %i for a signed integral typesigned integer type%d for a unsigned integral typeunsigned integer type%u
23.2 [container.requirements] table 80...
Table 89: Container requirements
expression return type operational semantics assertion/note/pre/post-condition complexity X::difference_type signed integral typesigned integer typeis identical to the difference type of X::iterator and X::const_iterator compile time X::size_type unsigned integral typeunsigned integer typesize_type can represent any non-negative value of difference_type compile time
X [iterator.concepts] paragraph 1...
Iterators are a generalization of pointers that allow a C++ program to work with different data structures (containers) in a uniform manner. To be able to construct template algorithms that work correctly and efficiently on different types of data structures, the library formalizes not just the interfaces but also the semantics and complexity assumptions of iterators. All input iteratorsisupport the expression*i, resulting in a value of some class, enumeration, or built-in typeT, called the value type of the iterator. All output iterators support the expression*i = owhereois a value of some type that is in the set of types that are writable to the particular iterator type ofi. All iteratorsifor which the expression(*i).mis well-defined, support the expressioni->mwith the same semantics as(*i).m. For every iterator typeXfor which equality is defined, there is a correspondingsigned integral typesigned integer type called the difference type of the iterator.
I'm a little unsure of this change. Previously this paragraph would allow instantiations of linear_congruential_engine on char, wchar_t, bool, and other types. The new wording prohibits this. 26.5.3.1 [rand.eng.lcong] paragraph 2...
The template parameterUIntTypeshall denote anunsigned integral typeunsigned integer type large enough to store values as large asm - 1. If the template parametermis 0, the modulusmused throughout this section 26.4.3.1 isnumeric_limits<result_type>::max()plus 1. [Note: The result need not be representable as a value of typeresult_type. --end note] Otherwise, the following relations shall hold:a < mandc < m.
Same rationale as the previous change. X [rand.adapt.xor] paragraph 6...
BothEngine1::result_typeandEngine2::result_typeshall denote (possibly different)unsigned integral typesunsigned integer types. The member result_type shall denote either the type Engine1::result_type or the type Engine2::result_type, whichever provides the most storage according to clause 3.9.1.
26.5.7.1 [rand.util.seedseq] paragraph 7...
Requires:RandomAccessIteratorshall meet the requirements of a random access iterator (24.1.5) such thatiterator_traits<RandomAccessIterator>::value_typeshall denote anunsigned integral typeunsigned integer type capable of accomodating 32-bit quantities.
By making this change, integral types that happen to have a signed representation, but are not signed integer types, would no longer be required to use a two's complement representation. This may go against the original intent, and should be reviewed. 29.6 [atomics.types.operations] paragraph 24...
Remark: Forsigned integral typessigned integer types, arithmetic is defined using two's complement representation. There are no undefined results. For address types, the result may be an undefined address, but the operations otherwise have no undefined behavior.
Section: 26.5.8.5.1 [rand.dist.samp.discrete] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2008-08-22 Last modified: 2009-03-09
View all other issues in [rand.dist.samp.discrete].
View all issues with NAD Editorial status.
Discussion:
During the Sophia Antipolis meeting it was decided to separate from 793 a subrequest that adds initializer list support to discrete_distribution, specifically, the issue proposed to add a c'tor taking a initializer_list<double>.
Proposed resolution:
In 26.5.8.5.1 [rand.dist.samp.discrete]/1, class discrete_distribution, just before the member declaration
explicit discrete_distribution(const param_type& parm);
insert
discrete_distribution(initializer_list<double> wl);
Between p.4 and p.5 of the same section insert a new paragraph as part of the new member description:
discrete_distribution(initializer_list<double> wl);Effects: Same as discrete_distribution(wl.begin(), wl.end()).
Rationale:
Addressed by N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X".Section: 26.5.8.5.2 [rand.dist.samp.pconst] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2008-08-22 Last modified: 2009-03-09
View all other issues in [rand.dist.samp.pconst].
View all issues with NAD Editorial status.
Discussion:
During the Sophia Antipolis meeting it was decided to separate from 794 a subrequest that adds initializer list support to piecewise_constant_distribution, specifically, the issue proposed to add a c'tor taking a initializer_list<double> and a Callable to evaluate weight values. For consistency with the remainder of this class and the remainder of the initializer_list-aware library the author decided to change the list argument type to the template parameter RealType instead. For the reasoning to use Func instead of Func&& as c'tor function argument see issue 793.
Proposed resolution:
Non-concept version of the proposed resolution
In 26.5.8.5.2 [rand.dist.samp.pconst]/1, class piecewise_constant_distribution, just before the member declaration
explicit piecewise_constant_distribution(const param_type& parm);
insert
template<typename Func> piecewise_constant_distribution(initializer_list<RealType> bl, Func fw);
Between p.4 and p.5 of the same section insert a series of new paragraphs nominated below as [p5_1], [p5_2], and [p5_3] as part of the new member description:
template<typename Func> piecewise_constant_distribution(initializer_list<RealType> bl, Func fw);[p5_1] Complexity: Exactly nf = max(bl.size(), 1) - 1 invocations of fw.
[p5_2] Requires:
- fw shall be callable with one argument of type RealType, and shall return values of a type convertible to double;
- The relation 0 < S = w0+. . .+wn-1 shall hold. For all sampled values xk defined below, fw(xk) shall return a weight value wk that is non-negative, non-NaN, and non-infinity;
- If nf > 0 let bk = *(bl.begin() + k), k = 0, . . . , bl.size()-1 and the following relations shall hold for k = 0, . . . , nf-1: bk < bk+1.
[p5_3] Effects:
If nf == 0,
- lets the sequence w have length n = 1 and consist of the single value w0 = 1, and
- lets the sequence b have length n+1 with b0 = 0 and b1 = 1.
Otherwise,
- sets n = nf, and [bl.begin(), bl.end()) shall form the sequence b of length n+1, and
lets the sequences w have length n and for each k = 0, . . . ,n-1, calculates:
xk = 0.5*(bk+1 + bk) wk = fw(xk)Constructs a piecewise_constant_distribution object with the above computed sequence b as the interval boundaries and with the probability densities:
ρk = wk/(S * (bk+1 - bk)) for k = 0, . . . , n-1.
Concept version of the proposed resolution
In 26.5.8.5.2 [rand.dist.samp.pconst]/1, class piecewise_constant_distribution, just before the member declaration
explicit piecewise_constant_distribution(const param_type& parm);
insert
template<Callable<auto, RealType> Func> requires Convertible<Func::result_type, double> piecewise_constant_distribution(initializer_list<RealType> bl, Func fw);
Between p.4 and p.5 of the same section insert a series of new paragraphs nominated below as [p5_1], [p5_2], and [p5_3] as part of the new member description:
template<Callable<auto, RealType> Func> requires Convertible<Func::result_type, double> piecewise_constant_distribution(initializer_list<RealType> bl, Func fw);[p5_1] Complexity: Exactly nf = max(bl.size(), 1) - 1 invocations of fw.
[p5_2] Requires:
- The relation 0 < S = w0+. . .+wn-1 shall hold. For all sampled values xk defined below, fw(xk) shall return a weight value wk that is non-negative, non-NaN, and non-infinity;
- If nf > 0 let bk = *(bl.begin() + k), k = 0, . . . , bl.size()-1 and the following relations shall hold for k = 0, . . . , nf-1: bk < bk+1.
[p5_3] Effects:
If nf == 0,
- lets the sequence w have length n = 1 and consist of the single value w0 = 1, and
- lets the sequence b have length n+1 with b0 = 0 and b1 = 1.
Otherwise,
- sets n = nf, and [bl.begin(), bl.end()) shall form the sequence b of length n+1, and
lets the sequences w have length n and for each k = 0, . . . ,n-1, calculates:
xk = 0.5*(bk+1 + bk) wk = fw(xk)Constructs a piecewise_constant_distribution object with the above computed sequence b as the interval boundaries and with the probability densities:
ρk = wk/(S * (bk+1 - bk)) for k = 0, . . . , n-1.
Rationale:
Addressed by N2836 "Wording Tweaks for Concept-enabled Random Number Generation in C++0X".Section: 17 [library] Status: NAD Future Submitter: Martin Sebor Opened: 2008-08-23 Last modified: 2009-07-17
View other active issues in [library].
View all other issues in [library].
View all issues with NAD Future status.
Discussion:
Recent changes to the working draft have introduced a gratuitous inconsistency with the C++ 2003 version of the specification with respect to exception guarantees provided by standard functions. While the C++ 2003 standard consistenly uses the empty exception specification, throw(), to declare functions that are guaranteed not to throw exceptions, the current working draft contains a number of "Throws: Nothing." clause to specify essentially the same requirement. The difference between the two approaches is that the former specifies the behavior of programs that violate the requirement (std::unexpected() is called) while the latter leaves the behavior undefined.
A survey of the working draft reveals that there are a total of 209 occurrences of throw() in the library portion of the spec, the majority in clause 18, a couple (literally) in 19, a handful in 20, a bunch in 22, four in 24, one in 27, and about a dozen in D.9.
There are also 203 occurrences of "Throws: Nothing." scattered throughout the spec.
While sometimes there are good reasons to use the "Throws: Nothing." approach rather than making use of throw(), these reasons do not apply in most of the cases where this new clause has been introduced and the empty exception specification would be a better approach.
First, functions declared with the empty exception specification permit compilers to generate better code for calls to such functions. In some cases, the compiler might even be able to eliminate whole chunks of user-written code when instantiating a generic template on a type whose operations invoked from the template specialization are known not to throw. The prototypical example are the std::uninitialized_copy() and std::uninitialized_fill() algorithms where the entire catch(...) block can be optimized away.
For example, given the following definition of the std::uninitialized_copy function template and a user-defined type SomeType:
template <class InputIterator, class ForwardIterator>
ForwardIterator
uninitialized_copy (InputIterator first, InputIterator last, ForwardIterator res)
{
typedef iterator_traits<ForwardIterator>::value_type ValueType;
ForwardIterator start = res;
try {
for (; first != last; ++first, ++res)
::new (&*res) ValueType (*first);
}
catch (...) {
for (; start != res; --start)
(&*start)->~ValueType ();
throw;
}
return res;
}
struct SomeType {
SomeType (const SomeType&) throw ();
}
compilers are able to emit the following efficient specialization of std::uninitialized_copy<const SomeType*, SomeType*> (note that the catch block has been optimized away):
template <> SomeType*
uninitialized_copy (const SomeType *first, const SomeType *last, SomeType *res)
{
for (; first != last; ++first, ++res)
::new (res) SomeType (*first);
return res;
}
Another general example is default constructors which, when decorated with throw(), allow the compiler to eliminate the implicit try and catch blocks that it otherwise must emit around each the invocation of the constructor in new-expressions.
For example, given the following definitions of class MayThrow and WontThrow and the two statements below:
struct MayThrow {
MayThrow ();
};
struct WontThrow {
WontThrow () throw ();
};
MayThrow *a = new MayThrow [N];
WontThrow *b = new WontThrow [N];
the compiler generates the following code for the first statement:
MayThrow *a;
{
MayThrow *first = operator new[] (N * sizeof (*a));
MayThrow *last = first + N;
MayThrow *next = first;
try {
for ( ; next != last; ++next)
new (next) MayThrow;
}
catch (...) {
for ( ; first != first; --next)
next->~MayThrow ();
operator delete[] (first);
throw;
}
a = first;
}
but it is can generate much more compact code for the second statement:
WontThrow *b = operator new[] (N * sizeof (*b)); WontThrow *last = b + N; for (WontThrow *next = b; next != last; ++next) new (next) WontThrow;
Second, in order for users to get the maximum benefit out of the new std::has_nothrow_xxx traits when using standard library types it will be important for implementations to decorate all non throwing copy constructors and assignment operators with throw(). Note that while an optimizer may be able to tell whether a function without an explicit exception specification can throw or not based on its definition, it can only do so when it can see the source code of the definition. When it can't it must assume that the function may throw. To prevent violating the One Definition Rule, the std::has_nothrow_xxx trait must return the most pessimistic guess across all translation units in the program, meaning that std::has_nothrow_xxx<T>::value must evaluate to false for any T whose xxx (where xxx is default or copy ctor, or assignment operator) is defined out-of-line.
Counterarguments:
During the discussion of this issue on c++std-lib@accu.org (starting with post c++std-lib-21950) the following arguments in favor of the "Throws: Nothing." style have been made.
The answer to point (1) above is that implementers can (and some have) declare functions with throw() to indicate to the compiler that calls to the function can safely be assumed not to throw in order to allow it to generate efficient code at the call site without also having to define the functions the same way and causing the compiler to generate suboptimal code for the function definition. That is, the function is declared with throw() in a header but it's defined without it in the source file. The throw() declaration is suppressed when compiling the definition to avoid compiler errors. This technique, while strictly speaking no permitted by the language, is safe and has been employed in practice. For example, the GNU C library takes this approach. Microsoft Visual C++ takes a similar approach by simply assuming that no function with C language linkage can throw an exception unless it's explicitly declared to do so using the language extension throw(...).
Our answer to point (2) above is that there is no existing practice where C++ Standard Library implementers have opted to make use of the proprietary mechanisms to declare functions that don't throw. The language provides a mechanism specifically designed for this purpose. Avoiding its use in the specification itself in favor of proprietary mechanisms defeats the purpose of the feature. In addition, making use of the empty exception specification inconsistently, in some areas of the standard, while conspicuously avoiding it and making use of the "Throws: Nothing." form in others is confusing to users.
The answer to point (3) is simply to exercise caution when declaring functions and especially function templates with the empty exception specification. Functions that required not to throw but that may call back into user code are poor candidates for the empty exception specification and should instead be specified using "Throws: Nothing." clause.
[ 2009-07 Frankfurt ]
We need someone to do an extensive review.
NAD Future.
Proposed resolution:
We propose two possible solutions. Our recommendation is to adopt Option 1 below.
Option 1:
Except for functions or function templates that make calls back to user-defined functions that may not be declared throw() replace all occurrences of the "Throws: Nothing." clause with the empty exception specification. Functions that are required not to throw but that make calls back to user code should be specified to "Throw: Nothing."
Option 2:
For consistency, replace all occurrences of the empty exception specification with a "Throws: Nothing." clause.
Section: 20.8.12.2.4 [util.smartptr.shared.mod] Status: NAD Editorial Submitter: Jonathan Wakely Opened: 2008-09-15 Last modified: 2009-07-13
View all issues with NAD Editorial status.
Discussion:
#include <memory>
#include <cassert>
struct A { };
struct B : A { };
int main()
{
std::shared_ptr<A> pa(new A);
std::shared_ptr<B> pb(new B);
std::swap<A>(pa, pb); // N.B. no argument deduction
assert( pa.get() == pb.get() );
return 0;
}
Is this behaviour correct (I believe it is) and if so, is it unavoidable, or not worth worrying about?
This calls the lvalue/rvalue swap overload for shared_ptr:
template<class T> void swap( shared_ptr<T> & a, shared_ptr<T> && b );
silently converting the second argument from shared_ptr<B> to shared_ptr<A> and binding the rvalue ref to the produced temporary.
This is not, in my opinion, a shared_ptr problem; it is a general issue with the rvalue swap overloads. Do we want to prevent this code from compiling? If so, how?
Perhaps we should limit rvalue args to swap to those types that would benefit from the "swap trick". Or, since we now have shrink_to_fit(), just eliminate the rvalue swap overloads altogether. The original motivation was:
N1690.vector<A> v = ...; ... swap(v, vector<A>(v));
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to NAD Editorial.
Proposed resolution:
Recommend NAD Editorial, fixed by N2844.
Section: 23.3.3.5 [forwardlist.ops] Status: NAD Editorial Submitter: Ed Smith-Rowland Opened: 2008-09-15 Last modified: 2009-03-09
View other active issues in [forwardlist.ops].
View all other issues in [forwardlist.ops].
View all issues with NAD Editorial status.
Discussion:
I was looking at the latest draft on forward_list. Especially the splice methods.
The first one splices a whole list after a given iterator in this. The name is splice_after. I think in 23.3.3.5 [forwardlist.ops] paragraph 40 change:
Effect: Insert the contents of xbeforeafter position, ...
A deeper issue involves the complexity. forward_list has no size and we don't know when we've reached the end except to walk up to it. To splice we would need to hook the end of the source list to the item after position in this list. This would involve walking length of the source list until we got to the last dereference-able element in source. There's no way we could do this in O(1) unless we stored a bogus end in forward_list.
OTOH, the last version of splice_after with iterator ranges we could do in O(1) because we know how to hook the end of the source range to ...
Unless I'm misconceiving the whole thing. Which is possible. I'll look at it again.
I'm pretty sure about the first part though.
[ San Francisco: ]
This issue is more complicated than it looks.
paragraph 47: replace each (first, last) with (first, last]
add a statement after paragraph 48 that complexity is O(1)
remove the complexity statement from the first overload of splice_after
We may have the same problems with other modifiers, like erase_after. Should it require that all iterators in the range (position, last] be dereferenceable?
We do, however, like the proposed changes and consider them Editorial. Move to NAD Editorial, Pending. Howard to open a new issue to handle the problems with the complexity requirements.
Opened 897.
Proposed resolution:
In 23.3.3.5 [forwardlist.ops] paragraph 40 change:
Effect: Insert the contents of xbeforeafter position, ...
Section: 17.5.1.4 [structure.specifications] Status: Dup Submitter: James Dennett Opened: 2008-09-16 Last modified: 2009-07-17
View all other issues in [structure.specifications].
View all issues with Dup status.
Duplicate of: 625
Discussion:
Per discussion, we need an issue open to cover looking at "Requires" clauses which are not constraints on user code, such as that on std::basic_string::at.
[ 2009-07 Frankfurt ]
Alan to address in paper.
Proposed resolution:
Section: 24.5.2.5 [insert.iterator] Status: NAD Submitter: Alisdair Meredith Opened: 2008-09-24 Last modified: 2009-07-13
View all issues with NAD status.
Discussion:
Addresses UK 282
The requires clause on the const T & overloads in back_insert_iterator/front_insert_iterator/insert_iterator mean that the assignment operator will implicitly move from lvalues of a move-only type.
Suggested resolutions are:
[ Post Summit, Alisdair adds: ]
Both comment and issue have been resolved by the adoption of N2844 (rvalue references safety fix) at the last meeting.
Suggest resolve as NAD Editorial with a reference to the paper.
[ Batavia (2009-05): ]
We agree that this has been resolved in the latest Working Draft. Move to NAD.
Proposed resolution:
Recommend NAD, addressed by N2844.
Section: 18.3.1 [limits] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2008-09-24 Last modified: 2009-07-16
View all other issues in [limits].
View all issues with NAD Concepts status.
Discussion:
Addresses FR 32 and DE 16
numeric_limits has functions specifically designed to return NaNs, which break the model of Regular (via its axioms.) While floating point types will be acceptible in many algorithms taking Regular values, it is not appopriate for this specific API and we need a less refined constraint.
FR 32:
The definition of numeric_limits<> as requiring a regular type is both conceptually wrong and operationally illogical. As we pointed before, this mistake needs to be corrected. For example, the template can be left unconstrained. In fact this reflects a much more general problem with concept_maps/axioms and their interpretations. It appears that the current text heavily leans toward experimental academic type theory.
DE 16:
The class template numeric_limits should not specify the Regular concept requirement for its template parameter, because it contains functions returning NaN values for floating-point types; these values violate the semantics of EqualityComparable.
[ Summit: ]
Move to Open. Alisdair and Gaby will work on a solution, along with the new treatment of axioms in clause 14.
Proposed resolution:
Section: 24.5.2.1 [back.insert.iterator] Status: NAD Submitter: Dave Abrahams Opened: 2008-09-19 Last modified: 2009-07-16
View all issues with NAD status.
Discussion:
I just noticed this; don't know how far the problem(?) extends or whether it's new or existing: back_insert_iterator's operator* is not const, so you can't dereference a const one.
[ Post Summit Daniel adds: ]
If done, this change should be applied for front_insert_iterator, insert_iterator, ostream_iterator, and ostreambuf_iterator as well.
[ Batavia (2009-05): ]
Alisdair notes that these all are output iterators. Howard points out that ++*i would no longer work if we made this change.
Move to NAD.
[ 2009-05-25 Daniel adds: ]
Proposed resolution:
Section: 30.4.1.1 [thread.mutex.class] Status: Dup Submitter: Herb Sutter Opened: 2008-09-18 Last modified: 2009-03-22
View other active issues in [thread.mutex.class].
View all other issues in [thread.mutex.class].
View all issues with Dup status.
Duplicate of: 893
Discussion:
A few questions on the current WP, N2723:
30.4.1 [thread.mutex.requirements]/24 says an expression mut.unlock() "Throws: Nothing." I'm assuming that, per 17.6.3.11 [res.on.required], errors that violate the precondition "The calling thread shall own the mutex" opens the door for throwing an exception anyway, such as to report unbalanced unlock operations and unlocking from a thread that does not have ownership. Right?
30.4.1.1 [thread.mutex.class]/3 (actually numbered paragraph "27" in the WP; this is just a typo I think) says
The behavior of a program is undefined if:
- it destroys a mutex object owned by any thread,
- a thread that owns a mutex object calls lock() or try_lock() on that object, or
- a thread terminates while owning a mutex object.
As already discussed, I think the second bullet should be removed, and such a lock() or try_lock() should fail with an exception or returning false, respectively.
A potential addition to the list would be
but without that the status quo text endorses the technique of the program logically transferring ownership of a mutex to another thread with correctness enforced by programming discipline. Was that intended?
[ Summit: ]
Two resolutions: "not a defect" and "duplicate", as follows:
- 30.4.1 [thread.mutex.requirements]/24: NAD. If the precondition fails the program has undefined behaviour and therefore an implementation may throw an exception already.
- 30.4.1.1 [thread.mutex.class]/3 bullet 2: Already addressed by issue 893.
- 30.4.1.1 [thread.mutex.class]/3 proposed addition: NAD. This is already covered by the mutex requirements, which have ownership as a Precondition.
Proposed resolution:
Section: 18.9 [support.initlist] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2008-09-26 Last modified: 2009-07-16
View all issues with NAD Concepts status.
Discussion:
The currently proposed constraint on initializer_list's element type E is that is has to meet ObjectType. This is an underspecification, because both core language and library part of initializer_list make clear, that it references an implicitly allocated array:
8.5.4 [dcl.init.list]/4:
When an initializer list is implicitly converted to a std::initializer_list<E>, the object passed is constructed as if the implementation allocated an array of N elements of type E, where N is the number of elements in the initializer list.[..]
18.9 [support.initlist]/2.
An object of type initializer_list<E> provides access to an array of objects of type const E.[..]
Therefore, E needs to fulfill concept ValueType (thus excluding abstract class types). This stricter requirement should be added to prevent deep instantiation errors known from the bad old times, as shown in the following example:
// Header A: (Should concept-check even in stand-alone modus)
template <DefaultConstructible T>
requires MoveConstructible<T>
void generate_and_do_3(T a) {
std::initializer_list<T> list{T(), std::move(a), T()};
...
}
void do_more();
void do_more_or_less();
template <DefaultConstructible T>
requires MoveConstructible<T>
void more_generate_3() {
do_more();
generate_and_do_3(T());
}
template <DefaultConstructible T>
requires MoveConstructible<T>
void something_and_generate_3() {
do_more_or_less();
more_generate_3();
}
// Test.cpp
#include "A.h"
class Abstract {
public:
virtual ~Abstract();
virtual void foo() = 0; // abstract type
Abstract(Abstract&&){} // MoveConstructible
Abstract(){} // DefaultConstructible
};
int main() {
// The restricted template *accepts* the argument, but
// causes a deep instantiation error in the internal function
// generate_and_do_3:
something_and_generate_3<Abstract>();
}
The proposed stricter constraint does not minimize the aim to support more general containers for which ObjectType would be sufficient. If such an extended container (lets assume it's still a class template) provides a constructor that accepts an initializer_list only this constructor would need to be restricted on ValueType:
template<ObjectType T>
class ExtContainer {
public:
requires ValueType<T>
ExtContainer(std::initializer_list<T>);
...
};
[ Batavia (2009-05): ]
Move to Tentatively Ready.
[ 2009-07 Frankfurt: ]
Need to look at again without concepts.
Proposed resolution:
Section: 25.3.3 [alg.swap] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2008-10-01 Last modified: 2009-07-13
View all other issues in [alg.swap].
View all issues with NAD Concepts status.
Discussion:
With the adaption of 809 we have a new algorithm swap for C-arrays, which needs to be conceptualized.
[ Post Summit Daniel adds: ]
Recommend as NAD Editorial: The changes have already been applied to the WP N2800.
[ Batavia (2009-05): ]
Move to NAD; the changes have already been made.
Proposed resolution:
Replace in 25.3.3 [alg.swap] before p. 3 until p. 4 by
template <classValueType T, size_t N> requires Swappable<T> void swap(T (&a)[N], T (&b)[N]);
Requires: T shall be Swappable.Effects: swap_ranges(a, a + N, b);
Section: 25.3.5 [alg.replace] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2008-10-03 Last modified: 2009-07-14
View all other issues in [alg.replace].
View all issues with NAD Concepts status.
Discussion:
(A) 25.3.5 [alg.replace]/1:
Requires: The expression *first = new_value shall be valid.
(B) 25.3.5 [alg.replace]/4:
Requires: The results of the expressions *first and new_value shall be writable to the result output iterator.[..]
Since conceptualization, the quoted content of these clauses is covered by the existing requirements
(A) OutputIterator<Iter, const T&>
and
(B) OutputIterator<OutIter, InIter::reference> && OutputIterator<OutIter, const T&>
resp, and thus should be removed.
[ Batavia (2009-05): ]
We agree with the proposed resolution.
Move to Tentatively Ready.
Proposed resolution:
Remove 25.3.5 [alg.replace]/1.
template<ForwardIterator Iter, class T> requires OutputIterator<Iter, Iter::reference> && OutputIterator<Iter, const T&> && HasEqualTo<Iter::value_type, T> void replace(Iter first, Iter last, const T& old_value, const T& new_value); template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred, class T> requires OutputIterator<Iter, Iter::reference> && OutputIterator<Iter, const T&> && CopyConstructible<Pred> void replace_if(Iter first, Iter last, Pred pred, const T& new_value);1 Requires: The expression *first = new_value shall be valid.
25.3.5 [alg.replace]/4: Remove the sentence "The results of the expressions *first and new_value shall be writable to the result output iterator.".
template<InputIterator InIter, typename OutIter, class T> requires OutputIterator<OutIter, InIter::reference> && OutputIterator<OutIter, const T&> && HasEqualTo<InIter::value_type, T> OutIter replace_copy(InIter first, InIter last, OutIter result, const T& old_value, const T& new_value); template<InputIterator InIter, typename OutIter, Predicate<auto, InIter::value_type> Pred, class T> requires OutputIterator<OutIter, InIter::reference> && OutputIterator<OutIter, const T&> && CopyConstructible<Pred> OutIter replace_copy_if(InIter first, InIter last, OutIter result, Pred pred, const T& new_value);4 Requires:The results of the expressions *first and new_value shall be writable to the result output iterator.The ranges [first,last) and [result,result + (last - first)) shall not overlap.
Section: 25.3.9 [alg.unique] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2008-10-03 Last modified: 2009-07-14
View all other issues in [alg.unique].
View all issues with NAD Concepts status.
Discussion:
25.3.9 [alg.unique]/2: "Requires: The comparison function shall be an equivalence relation."
The essence of this is already covered by the given requirement
EquivalenceRelation<auto, Iter::value_type> Pred
and should thus be removed.
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to Tentatively Ready.
Proposed resolution:
Remove 25.3.9 [alg.unique]/2
template<ForwardIterator Iter> requires OutputIterator<Iter, Iter::reference> && EqualityComparable<Iter::value_type> Iter unique(Iter first, Iter last); template<ForwardIterator Iter, EquivalenceRelation<auto, Iter::value_type> Pred> requires OutputIterator<Iter, RvalueOf<Iter::reference>::type> && CopyConstructible<Pred> Iter unique(Iter first, Iter last, Pred pred);1 Effects: ...
2 Requires: The comparison function shall be an equivalence relation.
Section: 20.5.2.3 [tuple.swap] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2008-10-04 Last modified: 2009-07-13
View all issues with NAD Concepts status.
Discussion:
Issue 522 was accepted after tuple had been conceptualized, therefore this step needs to be completed.
[ Post Summit Daniel adds ]
This is now NAD Editorial (addressed by N2844) except for item 3 in the proposed wording.
[ 2009-05-01 Daniel adds: ]
As of the recent WP (N2857), this issue is now completely covered by editorial changes (including the third bullet), therefore I unconditionally recommend NAD.
[ Batavia (2009-05): ]
We observed that all the proposed changes have already been applied to the Working Draft, rendering this issue moot.
Move to NAD.
Proposed resolution:
In both 20.5.1 [tuple.general]/2 and 20.5.2.9 [tuple.special] change
template <classSwappable... Types> void swap(tuple<Types...>& x, tuple<Types...>& y);
In 20.5.2 [tuple.tuple], class tuple definition and in 20.5.2.3 [tuple.swap], change
requires Swappable<Types>...void swap(tuple&);
In 20.5.2.3 [tuple.swap] remove the current requires-clause, which says:
Requires: Each type in Types shall be Swappable
Section: X [allocator.concepts] Status: NAD Concepts Submitter: Pablo Halpern Opened: 2008-10-23 Last modified: 2009-07-13
View all issues with NAD Concepts status.
Discussion:
X [allocator.concepts] contains a reference to a concept named Dereferenceable. No such concept exists.
[ Daniel adds 2009-02-14: ]
The proposal given in the paper N2829 would automatically resolve this issue.
[ Batavia (2009-05): ]
This particular set of changes has already been made. There are two related changes later on (and possibly also an earlier Example); these can be handled editorially.
Move to NAD Editorial.
Proposed resolution:
Change all uses of the concept Dereferenceable to HasDereference in X [allocator.concepts].
Section: 20.5.2.7 [tuple.rel] Status: NAD Concepts Submitter: Joe Gottman Opened: 2008-10-28 Last modified: 2009-07-13
View all other issues in [tuple.rel].
View all issues with NAD Concepts status.
Discussion:
In the latest working draft for C++0x, tuple's operator== and operator< are declared as
template<class... TTypes, class... UTypes> requires EqualityComparable<TTypes, UTypes>... bool operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
and
template<class... TTypes, class... UTypes> requires LessThanComparable<TTypes, UTypes>... bool operator<(const tuple<TTypes...>& t, const tuple<UTypes...>& u);
But the concepts EqualityComparable and LessThanComparable only take one parameter, not two. Also, even if LessThanComparable could take two parameters, the definition of tuple::operator<() should also require
LessThanComparable<UTypes, TTypes>... // (note the order)
since the algorithm for tuple::operator< is the following (pseudo-code)
for (size_t N = 0; N < sizeof...(TTypes); ++N) {
if (get<N>(t) < get<N>(u) return true;
else if ((get<N>(u) < get<N>(t)) return false;
}
return false;
Similar problems hold for tuples's other comparison operators.
[ Post Summit: ]
Recommend Tentatively Ready.
Proposed resolution:
In 20.5.1 [tuple.general] and 20.5.2.7 [tuple.rel] change:
template<class... TTypes, class... UTypes> requiresEqualityComparableHasEqualTo<TTypes, UTypes>... bool operator==(const tuple<TTypes...>&, const tuple<UTypes...>&); template<class... TTypes, class... UTypes> requiresLessThanComparableHasLess<TTypes, UTypes>... && HasLess<UTypes, TTypes>... bool operator<(const tuple<TTypes...>&, const tuple<UTypes...>&); template<class... TTypes, class... UTypes> requiresEqualityComparableHasEqualTo<TTypes, UTypes>... bool operator!=(const tuple<TTypes...>&, const tuple<UTypes...>&); template<class... TTypes, class... UTypes> requiresLessThanComparableHasLess<UTTypes,TUTypes>... && HasLess<UTypes, TTypes>... bool operator>(const tuple<TTypes...>&, const tuple<UTypes...>&); template<class... TTypes, class... UTypes> requiresLessThanComparableHasLess<UTTypes,TUTypes>... && HasLess<UTypes, TTypes>... bool operator<=(const tuple<TTypes...>&, const tuple<UTypes...>&); template<class... TTypes, class... UTypes> requiresLessThanComparableHasLess<TTypes, UTypes>... && HasLess<UTypes, TTypes>... bool operator>=(const tuple<TTypes...>&, const tuple<UTypes...>&);
Section: 29 [atomics] Status: NAD Editorial Submitter: Clark Nelson Opened: 2008-12-05 Last modified: 2009-05-23
View other active issues in [atomics].
View all other issues in [atomics].
View all issues with NAD Editorial status.
Discussion:
Addresses US 89
The types in the table "Atomics for standard typedef types" should be typedefs, not classes. These semantics are necessary for compatibility with C.
Change the classes to typedefs.
N2427 specified different requirements for atomic analogs of fundamental integer types (such as atomic_int) and for atomic analogs of <cstdint> typedefs (such as atomic_size_t). Specifically, atomic_int et al. were specified to be distinct classes, whereas atomic_size_t et al. were specified to be typedefs. Unfortunately, in applying N2427 to the WD, that distinction was erased, and the atomic analog of every <cstdint> typedef is required to be a distinct class.
It shouldn't be required that the atomic analog of every <cstdint> typedef be a typedef for some fundamental integer type. After all, <cstdint> is supposed to provide standard names for extended integer types. So there was a problem in N2427, which certainly could have been interpreted to require that. But the status quo in the WD is even worse, because it's unambiguously wrong.
What is needed are words to require the existence of a bunch of type names, without specifying whether they are class names or typedef names.
[ Summit: ]
Change status to NAD, editorial. See US 89 comment notes above.
Direct the editor to turn the types into typedefs as proposed in the comment. Paper approved by committee used typedefs, this appears to have been introduced as an editorial change. Rationale: for compatibility with C.
Proposed resolution:
Section: 17 [library] Status: NAD Submitter: Niels Dekker Opened: 2008-12-18 Last modified: 2009-07-17
View other active issues in [library].
View all other issues in [library].
View all issues with NAD status.
Discussion:
The assignment and equality operators = and == are easily confused, just because of their visual similarity, and in this case a simple typo can cause a serious bug. When the left side of an operator= is an rvalue, it's highly unlikely that the assignment was intended by the programmer:
if ( func() = value ) // Typical typo: == intended!
Built-in types don't support assignment to an rvalue, but unfortunately, a lot of types provided by the Standard Library do.
Fortunately the language now offers a syntax to prevent a certain member function from having an rvalue as *this: by adding a ref-qualifier (&) to the member function declaration. Assignment operators are explicitly mentioned as a use case of ref-qualifiers, in "Extending Move Semantics To *this (Revision 1)", N1821 by Daveed Vandevoorde and Bronek Kozicki
Hereby I would like to propose adding ref-qualifiers to all appropriate assignment operators in the library.
[ Batavia (2009-05): ]
Move to Open. We recommend this be deferred until after the next Committee Draft.
[ Frankfurt 2009-07: ]
The LWG declined to move forward with N2819.
Moved to NAD.
Proposed resolution:
A proposed resolution is provided by the paper on this subject, N2819, Ref-qualifiers for assignment operators of the Standard Library
Section: 29 [atomics] Status: Dup Submitter: Holger Grund Opened: 2008-12-19 Last modified: 2009-03-22
View other active issues in [atomics].
View all other issues in [atomics].
View all issues with Dup status.
Duplicate of: 880
Discussion:
I'm looking at 29 [atomics] and can't really make sense of a couple of things.
Firstly, there appears to be a typo in the <cstdatomic> synopsis:
The atomic_exchange overload taking an atomic_address is missing the second parameter:
void* atomic_exchange(volatile atomic_address*);should be
void* atomic_exchange(volatile atomic_address*, void*);Note, that this is not covered by 880 "Missing atomic exchange parameter", which only talks about the atomic_bool.
Proposed resolution:
Change the synopsis in 29 [atomics]/2:
void* atomic_exchange(volatile atomic_address*, void*);
Section: 20.9.5.1 [time.clock.system] Status: NAD Editorial Submitter: Pete Becker Opened: 2008-12-19 Last modified: 2009-07-13
View all other issues in [time.clock.system].
View all issues with NAD Editorial status.
Discussion:
In 20.9.5.1 [time.clock.system], the declaration of system_clock::rep says "see below", but there is nothing below that describes it.
[ Howard adds: ]
This note refers to:
-2- system_clock::duration::min() < system_clock::duration::zero() shall be true.I.e. this is standardeze for "system_clock::rep is signed". Perhaps an editorial note along the lines of:
-2- system_clock::duration::min() < system_clock::duration::zero() shall be true. [Note: system_clock::rep shall be signed. -- end note].?
[ Batavia (2009-05): ]
We agree with the direction of the proposed resolution. Move to NAD Editorial.
Proposed resolution:
Add a note to 20.9.5.1 [time.clock.system], p2:
-2- system_clock::duration::min() < system_clock::duration::zero() shall be true. [Note: system_clock::rep shall be signed. -- end note].
Section: 20.9.3.7 [time.duration.cast] Status: NAD Submitter: Pete Becker Opened: 2008-12-20 Last modified: 2009-07-13
View all other issues in [time.duration.cast].
View all issues with NAD status.
Discussion:
20.9.3.7 [time.duration.cast]/3:.... All intermediate computations shall be carried out in the widest possible representation... .
So ignoring floating-point types for the moment, all this arithmetic has to be done using the implementation's largest integral type, even if both arguments use int for their representation. This seems excessive. And it's not at all clear what this means if we don't ignore floating-point types.
This issue is related to 952.
[ Howard adds: ]
The intent of this remark is that intermediate computations are carried out using:
common_type<typename ToDuration::rep, Rep, intmax_t>::typeThe Remark was intended to be clarifying prose supporting the rather algorithmic description of the previous paragraph. I'm open to suggestions. Perhaps the entire paragraph 3 (Remarks) would be better dropped?
[ Batavia (2009-05): ]
We view this as a specific case of issue 952, and should be resolved when that issue is resolved.
Move to NAD.
Proposed resolution:
Section: 20.9.3.7 [time.duration.cast] Status: NAD Editorial Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2009-07-13
View all other issues in [time.duration.cast].
View all issues with NAD Editorial status.
Discussion:
20.9.3.7 [time.duration.cast] specifies an implementation and imposes requirements in text (and the implementation doesn't satisfy all of the text requirements). Pick one.
This issue is related to 946.
[ 2009-05-10 Howard adds: ]
The Remarks paragraph is an English re-statement of the preceeding Returns clause. It was meant to be clarifying and motivating, not confusing. I'm not aware with how the Remarks contradicts the Returns clause but I'm ok with simply removing the Remarks.
[ Batavia (2009-05): ]
Pete suggests that this could be resolved by rephrasing the Remarks to Notes.
Move to NAD Editorial.
Proposed resolution:
Section: 25.2.4 [alg.foreach] Status: NAD Editorial Submitter: Stephan T. Lavavej Opened: 2009-01-12 Last modified: 2009-07-13
View all other issues in [alg.foreach].
View all issues with NAD Editorial status.
Discussion:
Library Issue 475 has CD1 status, but the non-normative note in N2723 was removed in N2798 (25.2.4 [alg.foreach] in both drafts).
[ Batavia (2009-05): ]
Move to NAD Editorial.
Proposed resolution:
Restore the non-normative note. It might need to be expressed in terms of concepts.
Section: 17 [library] Status: NAD Editorial Submitter: Niels Dekker Opened: 2009-01-07 Last modified: 2009-07-13
View other active issues in [library].
View all other issues in [library].
View all issues with NAD Editorial status.
Discussion:
Previous versions of the Draft had a table, defining the Assignable requirement. For example N2134 Table 79, "Assignable requirements". But I guess the term "Assignable" is outdated by now, because the current Committee Draft provides MoveAssignable, CopyAssignable, and TriviallyCopyAssignable concepts instead. And as far as I can see, it no longer has a definition of Assignable. (Please correct me if I'm wrong.) Still the word "Assignable" is used in eight places in the Draft, N2800.
Are all of those instances of "Assignable" to be replaced by "CopyAssignable"?
[ Batavia (2009-05): ]
Move to NAD Editorial.
Proposed resolution:
Change Exception Propagation 18.8.5 [propagation]:
exception_ptr shall be DefaultConstructible, CopyConstructible, CopyAssignable and EqualityComparable.
Change Class template reference_wrapper 20.7.5 [refwrap]:
reference_wrapper<T> is a CopyConstructible and CopyAssignable wrapper around a reference to an object of type T.
Change Placeholders 20.7.11.1.4 [func.bind.place]:
It is implementation defined whether placeholder types are CopyAssignable. CopyAssignable placeholders' copy assignment operators shall not throw exceptions.
Change Class template shared_ptr 20.8.12.2 [util.smartptr.shared]:
Specializations of shared_ptr shall be CopyConstructible, CopyAssignable, and LessThanComparable...
Change Class template weak_ptr 20.8.12.3 [util.smartptr.weak]:
Specializations of weak_ptr shall be CopyConstructible, CopyAssignable, and LessThanComparable...
Change traits typedefs 21.2.2 [char.traits.typedefs] (note: including deletion of reference to 23.1!):
Requires: state_type shall meet the requirements of CopyAssignable(23.1), CopyConstructible (20.1.8), and DefaultConstructible types.
Change Class seed_seq 26.5.7.1 [rand.util.seedseq] (note again: including deletion of reference to 23.1!):
In addition to the requirements set forth below, instances of seed_seq shall meet the requirements of CopyConstructible (20.1.8) and of CopyAssignable(23.1).
Note: The proposed resolution of this issue does not deal with the instance of the term "Assignable" in D.9.1 [auto.ptr], as this is dealt with more specifically by LWG 973, "auto_ptr characteristics", submitted by Maarten Hilferink.
Section: D.9.1 [auto.ptr] Status: NAD Editorial Submitter: Maarten Hilferink Opened: 2009-01-21 Last modified: 2009-07-13
View all other issues in [auto.ptr].
View all issues with NAD Editorial status.
Discussion:
I think that the Note of D.9.1 [auto.ptr], paragraph 3 needs a rewrite since "Assignable" is no longer defined as a concept. The relationship of auto_ptr with the new CopyAssignable, MoveAssignable, and MoveConstructible concepts should be clarified. Furthermore, since the use of auto_ptr is depreciated anyway, we can also omit a description of its intended use.
[ Batavia (2009-05): ]
We agree with the intent of the proposed resolution. Move to NAD Editorial.
Proposed resolution:
Change D.9.1 [auto.ptr], paragraph 3:
The auto_ptr provides a semantics of strict ownership. An auto_ptr owns the ob ject it holds a pointer to. Copying an auto_ptr copies the pointer and transfers ownership to the destination. If more than one auto_ptr owns the same ob ject at the same time the behavior of the program is undefined. [Note: The uses of auto_ptr include providing temporary exception-safety for dynamically allocated memory, passing ownership of dynamically allocated memory to a function, and returning dynamically allocated memory from a function.auto_ptr does not meet the CopyConstructible and Assignable requirements for standard library container elements and thus instantiating a standard library container with an auto_ptr results in undefined behavior.Instances of auto_ptr shall meet the MoveConstructible and MoveAssignable requirements, but do not meet the CopyConstructible and CopyAssignable requirements. -- end note]
Section: 24.5.3 [move.iterators] Status: NAD Editorial Submitter: Howard Hinnant Opened: 2009-02-03 Last modified: 2009-07-13
View all issues with NAD Editorial status.
Discussion:
24.5.3 [move.iterators] has an incorrect example:
-2- [Example:
set<string> s; // populate the set s vector<string> v1(s.begin(), s.end()); // copies strings into v1 vector<string> v2(make_move_iterator(s.begin()), make_move_iterator(s.end())); // moves strings into v2-- end example]
One can not move from a set because the iterators return const references.
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to NAD Editorial.
Proposed resolution:
Change 24.5.3 [move.iterators]/2:
-2- [Example:
setlist<string> s; // populate thesetlist s vector<string> v1(s.begin(), s.end()); // copies strings into v1 vector<string> v2(make_move_iterator(s.begin()), make_move_iterator(s.end())); // moves strings into v2-- end example]
Section: 30.4.1 [thread.mutex.requirements] Status: NAD Submitter: Ion Gaztañaga Opened: 2009-02-07 Last modified: 2009-03-22
View other active issues in [thread.mutex.requirements].
View all other issues in [thread.mutex.requirements].
View all issues with NAD status.
Discussion:
POSIX 2008 adds two return values for pthread_mutex_xxxlock(): EOWNERDEAD (owner_dead) and ENOTRECOVERABLE (state_not_recoverable). In the first case the mutex is locked, in the second case the mutex is not locked.
Throwing an exception in the first case can be incompatible with the use of Locks, since the Lock::owns_lock() will be false when the lock is being destroyed.
Consider:
//Suppose mutex.lock() throws "owner_dead" unique_lock ul(&mutex); //mutex left locked if "owner_dead" is thrown
Throwing an exception with owner_dead might be also undesirable if robust-mutex support is added to C++ and the user has the equivalent of pthread_mutex_consistent() to notify the user has fixed the corrupted data and the mutex state should be marked consistent.
[ Summit: ]
Not a defect. Handling these error conditions is an implementation detail and must be handled below the C++ interface.
Proposed resolution:
Add to 30.4.1 [thread.mutex.requirements], p12:
-12- Error conditions:
- operation_not_permitted -- if the thread does not have the necessary permission to change the state of the mutex.
- resource_deadlock_would_occur -- if the current thread already owns the mutex and is able to detect it.
- device_or_resource_busy -- if the mutex is already locked and blocking is not possible.
- state_not_recoverable -- if the state protected by the mutex is not recoverable.
Section: X [concept.comparison] Status: NAD Submitter: Alisdair Meredith Opened: 2009-02-24 Last modified: 2009-07-16
View all other issues in [concept.comparison].
View all issues with NAD status.
Discussion:
X [concept.comparison] p2:
Due to the subtle meaning of == inside axioms, the Reflexivity axiom does not do anything as written. It merely states that a value is substitutable with itself, rather than asserting a property of the == operator.
Original proposed resolution:Change the definition of Reflexivity in X [concept.comparison]:
axiom Reflexivity(T a) { (a == a) == true; }
[ Post Summit: ]
Alisdair: I was wrong.
Recommend NAD.
Proposed resolution:
NAD.
Section: 17 [library] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-02-24 Last modified: 2009-07-16
View other active issues in [library].
View all other issues in [library].
View all issues with NAD Concepts status.
Discussion:
The example in 6.9p2 shows how late_check blocks inhibit concept_map lookup inside a constrained context, and so inhibit concept map adaption by users to meet template requirements.
Do we need some text in clause 17 prohibitting use of late_check in library template definitions unless otherwise documented?
[ Doug adds: ]
We need something like this, but it should be a more general statement about implementations respecting the concept maps provided by the user. Use of late_check is one way in which implementations can subvert the concept maps provided by the user, but there are other ways as well ("pattern-based" overloading, tricks with "auto" concept maps and defaulted associated type arguments).
[ Batavia (2009-05): ]
Move to Open, pending proposed wording from Alisdair and/or Doug for further review.
Proposed resolution:
Section: 17.6.1.1 [contents] Status: NAD Submitter: P.J. Plauger Opened: 2009-03-03 Last modified: 2009-07-22
View all other issues in [contents].
View all issues with NAD status.
Discussion:
Addresses UK 169
This phrasing contradicts later freedom to implement the C standard library portions in the global namespace as well as std. (17.6.2.3p4)
[ Batavia (2009-05): ]
The proposed wording seems to go too far. Move back to Open.
[ 2009-07 Frankfurt: ]
Howard to add NB reference to the description of this issue.
Move to NAD. This comment is informative and not normative by the use of the word "are" instead of the word "shall."
A note linking to Annex D would help clarify the intention, here.
Robert to Open a separate issue proposing that the standard C headers be undeprecated, for the purpose of clarifying the standard.
[ 2009-07-22 Bill modified the proposed wording with a clarifying footnote. ]
Proposed resolution:
Add a footnote to 17.6.1.1 [contents], p2:
-2- All library entities except macros, operator new and operator delete are defined within the namespace std or namespaces nested within namespace std*.
*The C standard library headers D.5 [depr.c.headers] also define names within the global namespace, while the C++ headers for C library facilities 17.6.1.2 [headers] may also define names within the global namespace.
Section: 17.5.1.3 [structure.requirements] Status: NAD Submitter: David Abrahams Opened: 2009-03-06 Last modified: 2009-07-13
View all issues with NAD status.
Discussion:
As a practical matter there's disagreement on the meaning of operational semantics. If the text in 17.5.1.3 [structure.requirements]p4 isn't clear, it should be clarified. However, it's not clear whether the disagreement is merely due to people not being aware of the text.
[ Batavia (2009-05): ]
Agree with the recommended NAD resolution.
Proposed resolution:
Recommend NAD. The text in 17.5.1.3 [structure.requirements] is perfectly clear.
Section: 25.2.8 [alg.adjacent.find] Status: NAD Concepts Submitter: Chris Jefferson Opened: 2009-03-09 Last modified: 2009-07-15
View all other issues in [alg.adjacent.find].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 296
adjacent_find in C++03 allows an arbitrary predicate, but in C++0x EqualityComparable/EquivalenceRelation is required. This forbids a number of use cases, including:
adjacent_find(begin, end, less<double>) Find the first place where a range is not ordered in decreasing order - in use to check for sorted ranges. adjacent_find(begin, end, DistanceBiggerThan(6) ) ) Find the first place in a range where values differ by more than a given value - in use to check an algorithm which produces points in space does not generate points too far apart.
A number of books use predicate which are not equivalence relations in examples, including "Thinking in C++" and "C++ Primer".
Adding the requirement that the predicate is an EquivalenceRelation does not appear to open up any possibility for a more optimised algorithm.
Proposed resolution:
Change the definition of adjacent_find in the synopsis of 25 [algorithms] and 25.2.8 [alg.adjacent.find] to:
template<ForwardIterator Iter> requiresEqualityComparableHasEqualTo<Iter::value_type, Iter::value_type> Iter adjacent_find(Iter first, Iter last); template<ForwardIterator Iter,EquivalenceRelationPredicate<auto, Iter::value_type, Iter::value_type> Pred> requires CopyConstructible<Pred> Iter adjacent_find(Iter first, Iter last, Pred pred);
Section: 17 [library] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-10 Last modified: 2009-07-18
View other active issues in [library].
View all other issues in [library].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 78
Related to 1063.
This is effectively an extension of LWG issue 343.
We know there is an increasing trend (encouraged by conformance testers and some users) that each library header should supply no more than required to satisfy the synopsis in the standard. This is typically achieved by breaking larger headers into smaller subsets, and judicious use of forward declarations.
If we apply this policy to C++0x (per N2800) it will be very surprising for people using library algorithms over ranges defined by pointers that they must #include <iterator_concepts> for their code to compile again. That is because pointers do not satisfy any of the iterator concepts without the concept_map supplied in this header.
Therefore, I suggest we should require all library headers that make use of iterator concepts are specifically required to #include <iterator_concepts>.
At a minimum, the list of headers would be: (assuming all are constrained by concepts)
algorithm array deque forward_list initializer_list iterator locale list map memory // if 1029 is adopted memory_concepts numeric random regex set string tuple unordered_map unordered_set utility vector
[ Ganesh adds: ]
The same problems exists for <memory_concepts> and <container_concepts>.
In order to compile <vector> you just need the definitions of the concepts in <memory_concepts>, the concept maps defined there are not necessary. Yet, from the user point of view, if the concept map template for AllocatableElement are not in scope, <vector> is pretty useless. Same for <tuple> and ConstructibleWithAllocator.
Similarly, <queue> is not very useful if the concept map template for QueueLikeContainer is not in scope, although the definition of concept alone is theoretically sufficient.
There's a pattern here: if a concept has concept maps "attached", they should never be separated.
[ Beman provided the proposed resolution for the May 2009 mailing. He comments: ]
Initially I tried to specify exactly what header should include what other headers. This was verbose, error prone, hard to maintain, and appeared to add little value compared to just stating the general rule.
[ Batavia (2009-05): ]
Pete believes the proposed wording overconstrains implementers. Instead of specifying the mechanism, he prefers a solution that spells out what needs to be declared, rather than how those declarations are to be provided, e.g.,
A C++ header shall provide the names that are required to be defined in that header.Bill suggests approaching the wording from a programmer's perspective. We may want to consider promising that certain widely-used headers (e.g., the concept headers) are included when needed by other headers. He feels, however, there is nothing broken now, although we may want to consider "something nicer."
Move to Open status.
[ 2009-06-16 Beman updated the proposed resolution: ]
- The mechanism is no longer specified, as requested in Batavia.
- The footnote has been removed since it specified mechanism and also did not reflect existing practice.
- A sentence was added that makes it clear that the existing practice is permitted.
[ 2009-07-15 Beman updated the proposed resolution: ]
[ 2009-07-17 Beman updated the proposed resolution based on feedback from the LWG in Frankfurt: ]
- Strike two pieces of text considered unnecessary.
- Change "definitions" to "declarations and definitions" in two places.
- Wording tightened slightly.
[ 2009-07 Frankfurt: ]
Revised Proposed Resolution:
A C++ header may include other C++ headers. A C++ header shall provide the declarations and definitions that appear in its synopsis (3.2 [basic.def.odr]). A C++ header shown in its synopsis as including other C++ headers shall provide the declarations and definitions that appear in the synopses of those other headers.
Alisdair: Does this address the BSI comment?
Beman: There were several overlapping comments. I tried to handle them all with one resolution.
Alisdair: I'd prefer to see this closed as NAD and have this resolution be the subject of some other, new issue.
Move to NAD Concepts. Howard to open a new issue (1178) in Ready state with the Proposed Resolution above. Beman will write up a discussion for the new issue.
Proposed resolution:
Change 17.6.4.2 [res.on.headers], Headers, paragraph 1, as indicated:
A C++ header may include other C++ headers.
[footnote]A C++ header shall provide the declarations and definitions that appear in its synopsis (3.2 [basic.def.odr]). A C++ header shown in its synopsis as including other C++ headers shall provide the same declarations and definitions as if those other headers were included.
[footnote] C++ headers must include a C++ header that contains any needed definition (3.2).
Section: 17.6.1.2 [headers] Status: NAD Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View all other issues in [headers].
View all issues with NAD status.
Discussion:
Addresses UK 170
One of goals of C++0x is to make language easier to teach and for 'incidental' programmers. The fine-grained headers of the C++ library are valuable in large scale systems for managing dependencies and optimising build times, but overcomplicated for simple development and tutorials. Add additional headers to support the whole library through a single include statement.
[ Batavia (2009-05): ]
We do not all agree that this is an issue, but we agree that if it needs solving this is the right way to do it. Move to Tentatively Ready.
[ 2009-07-06 Beman notes: ]
This issue adds a header <std>.
There is a paper to be looked at, N2905 Aggregation headers, that adds a header <std-all> that is the same thing except it excludes deprecated headers. N2905 also proposes a second aggregation header.
Seems like this issue should be held in abeyance until the LWG has had a chance to look at N2905.
[ 2009-07-06 Howard: I've pulled this issue back to Review. ]
[ 2009-07 Frankfurt ]
No consensus for change.
Proposed resolution:
Insert a new paragraph in 17.6.1.2 [headers] between p4 and p5
An additional header <std> shall have the effect of supplying the entire standard library. [Note: for example, it might be implemented as a file with an #include statement for each of the headers listed in tables 13 and 14. -- end note]
Section: 17.6.1.3 [compliance] Status: NAD Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-18
View all other issues in [compliance].
View all issues with NAD status.
Discussion:
Addresses JP 23
There is a freestanding implementation including <type_traits>, <array>, <ratio>, lately added to Table 13, C++ library headers. Programmers think them useful and hope that these headers are also added to Table 15, C++ headers for freestanding implementations, that shows the set of headers which a freestanding implementation shall include at least.
Original proposed resolution
Add <type_traits>, <array>, <ratio> to Table 15.
[ Summit: ]
The <array> header has far too many dependencies to require for a free-standing implementation.
The <ratio> header would be useful, has no dependencies, but is not strictly necessary.
The <type_traits> header is fundamentally a core language facility with a library interface, so should be supported.
(it is anticipated the resolution will come via an update to paper N2814) (see also LWG 833)
[ Batavia (2009-05): ]
Leave in Review status pending a paper on freestanding implementations by Martin Tasker.
[ 2009-07 Frankfurt: ]
Move this to NAD.
We considered all of the listed headers, and found a compelling case only for the inclusion of <type_traits> in the list of headers required of a freestanding implementation.
See Martin Tasker's paper Fixing Freestanding which provides the wording to include <type_traits> into freestanding implementations.
Proposed resolution:
Add <type_traits> to Table 15.
Section: 18.3.1.1 [numeric.limits] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View all issues with NAD Concepts status.
Discussion:
Addresses JP 26
numeric_limits [partial specializations] does not use concept.
[ Summit: ]
Alisdair will provide a soltion as part of treatment of axioms and LWG 902.
[ Post Summit: ]
Alisdair recommends NAD as the partial specializations are already constrained by requirements on the primary template.
[ Batavia (2009-05): ]
The Working Draft does not in general repeat a primary template's constraints in any specializations. Move to NAD.
[ 2009-05-25 Howard adds: ]
A c++std-lib thread starting at c++std-lib-23880 has cast doubt that NAD is the correct resolution of this issue. Indeed the discussion also casts doubt that the current proposed wording is the correct resolution as well. Personally I'm inclined to reset the status to Open. However I'm reverting the status to that which it had prior to the Batavia recommendation. I'm setting back to Review.
Proposed resolution:
Change 18.3.1.1 [numeric.limits]:
template<classRegular T> class numeric_limits<const T>; template<classRegular T> class numeric_limits<volatile T>; template<classRegular T> class numeric_limits<const volatile T>;
Section: 18.8.6 [except.nested] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View other active issues in [except.nested].
View all other issues in [except.nested].
View all issues with NAD Concepts status.
Discussion:
Addresses JP 29
throw_with_nested does not use concept.
[ Summit: ]
Agreed.
Proposed resolution:
Alisdair initially proposed wording in N2619.
We are awaiting an updated paper based on feedback from the San Francisco review.
Section: 24.2.5 [random.access.iterators] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-16
View other active issues in [random.access.iterators].
View all other issues in [random.access.iterators].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 263
This requirement on operator-= would be better expressed as a default implementation in the concept, with a matching axiom.
[ Batavia (2009-05): ]
The proposed resolution should also remove paragraph 5 and the declaration that precedes it. Further, we should provide an axiom that captures the desired semantics. This may be a broader policy to be applied. Move to Open.
Proposed resolution:
Change 24.2.5 [random.access.iterators]:
concept RandomAccessIterator<typename X> : BidirectionalIterator<X>, LessThanComparable<X> {
...
X& operator-=(X& x, difference_type n) { return x += -n; }
...
}
Section: 25.4.7 [alg.min.max] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-16
View all other issues in [alg.min.max].
View all issues with NAD Editorial status.
Discussion:
Addresses UK 305
The negative requirement on IsSameType is a hold-over from an earlier draught with a variadic template form of min/max algorith. It is no longer necessary.
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to Tentatively Ready.
[ 2009-07 Frankfurt ]
We believe this is NAD, but this needs to be reviewed against the post-remove-concepts draft.
Proposed resolution:
Change 25 [algorithms]:
template<class T, StrictWeakOrder<auto, T> Compare>requires !SameType<T, Compare> && CopyConstructible<Compare>const T& min(const T& a, const T& b, Compare comp); ... template<class T, StrictWeakOrder<auto, T> Compare>requires !SameType<T, Compare> && CopyConstructible<Compare>const T& max(const T& a, const T& b, Compare comp); ... template<class T, StrictWeakOrder<auto, T> Compare>requires !SameType<T, Compare> && CopyConstructible<Compare>pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp);
Change 25.4.7 [alg.min.max], p1, p9 and p17:
template<class T, StrictWeakOrder<auto, T> Compare>requires !SameType<T, Compare> && CopyConstructible<Compare>const T& min(const T& a, const T& b, Compare comp); ... template<class T, StrictWeakOrder<auto, T> Compare>requires !SameType<T, Compare> && CopyConstructible<Compare>const T& max(const T& a, const T& b, Compare comp); ... template<class T, StrictWeakOrder<auto, T> Compare>requires !SameType<T, Compare> && CopyConstructible<Compare>pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp);
Section: X [concept.transform] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View all other issues in [concept.transform].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 199
The requirement that programs do not supply concept_maps should probably be users do not supply their own concept_map specializations. The program will almost certainly supply concept_maps - the standard itself supplies a specialization for RvalueOf references. Note that the term program is defined in 3.5 [basic.link]p1 and makes no account of the standard library being treated differently to user written code.
[ 2009-05-09 Alisdair adds: ]
The same problem is present in the words added for the LvalueReference/RvalueReference concepts last meeting.
With three subsections requiring the same constraint, I'm wondering if there is a better way to organise this section. Possible 20.2.1 -> 20.2.3 belong in the fundamental concepts clause in [concept.support]? While they can be implemented purely as a library feature without additional compiler support, they are pretty fundamental and we want the same restriction on user-concept maps as is mandated there.
[ Batavia (2009-05): ]
We agree with the issue, but believe the wording needs further improvement. We want to investigate current definitions for nomenclature such as "user" and "program." Move to Open pending the recommended investigation.
Proposed resolution:
Change X [concept.transform] p2:
-2- Aprogramuser shall not provide concept maps for any concept in 20.1.1.
Change [concept.true] p2:
-2- Requires: aprogramuser shall not provide a concept map for the True concept.
Change [concept.classify] p2:
-2- Requires: aprogramuser shall not provide concept maps for any concept in this section.
Section: X [concept.comparison] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View all other issues in [concept.comparison].
View all issues with NAD Concepts status.
Discussion:
Addresses JP 33
LessThanComparable and EqualityComparable don't correspond to NaN.
Original proposed resolution:
Apply concept_map to these concepts at FloatingPointType.
[ Post Summit, Alisdair adds: ]
I don't understand the proposed resolution - there is no such thing as a 'negative' concept_map, and these concepts are auto concepts that match float/double etc. Also not clear how we are supposed to match values to concepts.
Recommend NAD and treat as a subset of issue 902.
Proposed resolution:
Recommend NAD.
Section: X [concept.regular] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View all issues with NAD Concepts status.
Discussion:
Addresses US 66
Application of the Regular concept to floating-point types appears to be controversial (see long discussion on std-lib reflector).
Original proposed resolution:
State that the Regular concept does not apply to floating-point types.
[ Summit: ]
Recommend that we handle the same as JP 33 / 1016.
[ Post Summit, Alisdair adds: ]
Recommend Open, and review after resolution of 902 and revised axiom feature.
Proposed resolution:
Section: 20.6 [meta] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View other active issues in [meta].
View all other issues in [meta].
View all issues with NAD Concepts status.
Discussion:
Addresses US 70
Specifications now expressed via narrative text are more accurately and clearly expressed via executable code.
Wherever concepts are available that directly match this section's type traits, express the traits in terms of the concepts instead of via narrative text. Where the type traits do not quite match the corresponding concepts, bring the two into alignment so as to avoid two nearly-identical notions.
[ Summit: ]
We think that this is a good idea, but it requires a lot of work. If someone submits a paper proposing specific changes, we would be happy to review it at the next meeting.
Proposed resolution:
Section: 20.8.12.6 [util.dynamic.safety] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-03-12
View all other issues in [util.dynamic.safety].
View all issues with NAD Editorial status.
Discussion:
Addresses UK 212
The pointer-safety API is nothing to do with smart pointers, so does not belong in 20.8.12 [util.smartptr]. In fact it is a set of language support features are really belongs in clause 18 [language.support], with the contents declared in a header that deals with language-support of memory management.
[ Summit: ]
Agree in principle, but not with the proposed resolution. We believe it belongs either a subsection of either 20 [utilities] or 20.8 [memory] as part of the general reorganization of 20 [utilities]. The declaration should stay in <memory>.
Proposed resolution:
Section: 20.7.15.2 [func.wrap.func] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-13
View all other issues in [func.wrap.func].
View all issues with NAD Editorial status.
Discussion:
Addresses DE 22
Related to issue 1114.
The conditions for deriving from std::unary_function and std::binary_function are unclear: The condition would also be satisfied if ArgTypes were std::vector<T1>, because it (arguably) "contains" T1.
[ Summit: ]
Agree. std::reference_wrapper has the same structure, and we suggest that std::function be presented in the same way as std::reference_wrapper.
[ 2009-05-09 Alisdair adds: ]
Phrasing should be "publicly and unambiguously derived from" and probably back in reference_wrapper too. Updated wording supplied.
[ Batavia (2009-05): ]
We agree with the proposed wording. Move to NAD Editorial.
Proposed resolution:
(no changes to <functional> synopsis required)
Change synopsis in Class template function 20.7.15.2 [func.wrap.func]:
template<Returnable R, CopyConstructible... ArgTypes> class function<R(ArgTypes...)> : public unary_function<T1, R> //iff sizeof...(ArgTypes) == 1 andsee below// ArgTypes contains T1: public binary_function<T1, T2, R> //iff sizeof...(ArgTypes) == 2 andsee below// ArgTypes contains T1 and T2{ ...
Add new p1/p2 before 20.7.15.2.1 [func.wrap.func.con]:
The template instantiation function<R(T1)> shall be publicly and unambiguously derived from std::unary_function<T1,R> if and only if the template type parameter is a function type taking one argument of type T1 and returning R.
The template instantiation function<R(T1,T2)> shall be publicly and unambiguously derived from std::binary_function<T1,T2,R> if and only if the template type parameter is a function type taking two arguments of type T1 and T2 and returning R.
explicit function();
Section: 20.7.15.2 [func.wrap.func] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-16
View all other issues in [func.wrap.func].
View all issues with NAD Concepts status.
Discussion:
Addresses JP 39
There are no requires corresponding to F of std::function.
[ 2009-05-01 Daniel adds: ]
1070 removes the second constructor.
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to Tentatively Ready. If issue 1070 is accepted, the changes to the second constructor in this issue are moot.
[ 2009-07 Frankfurt: ]
Constructors have no definition.
Proposed resolution:
Correct as follows in 20.7.15.2 [func.wrap.func] (class definition)
template<class F, Allocator Alloc>
requires ConstructibleWithAllocator<F, Alloc>
&& call=Callable<F, ArgTypes...>
&& Convertible<call::result_type, R>
function(allocator_arg_t, const Alloc&, F);
template<class F, Allocator Alloc>
requires ConstructibleWithAllocator<F,Alloc>
&& call=Callable<F, ArgTypes...>
&& Convertible<call::result_type, R>
function(allocator_arg_t, const Alloc&, F&&);
Section: 20.7.16 [unord.hash] Status: NAD Future Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-03-12
View other active issues in [unord.hash].
View all other issues in [unord.hash].
View all issues with NAD Future status.
Discussion:
Addresses UK 208
std::hash should be implemented for much more of the standard library. In particular for pair, tuple and all the standard containers.
Proposed resolution:
Section: 20.8 [memory] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View all other issues in [memory].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 209
Smart pointers cannot be used in constrained templates.
[ Summit: ]
We look forward to a paper on this topic. We recommend no action until a paper is available. We understand that a paper is forthcoming.
[ Peter Dimov adds: ]
shared_ptr<T> and weak_ptr<T> support all types T for which T* is valid. In other words, a possible (partial) resolution is to change class T to PointeeType T for shared_ptr, weak_ptr and possibly enable_shared_from_this.
Proposed resolution:
Section: 20.8.5 [default.allocator] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-15
View all issues with NAD Concepts status.
Discussion:
Addresses UK 213
std::allocator should be constrained to simplify its use on constrained contexts. This library component models allocation from free store via the new operator so choose constraints to match. The Allocator concept allows for a wider variety of allocators that users may choose to supply if their allocation model does not require operator new, without impacting the requirements of this template.
Suggested direction:
The primary allocator template should be constrained to require ObjectType<T> and FreeStoreAllocatable<T>. Further operations to be constrained as required.
[ Summit: ]
Agree as stated. A future paper will address additional related issues.
Proposed resolution:
Section: 20.8.7 [storage.iterator] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-16
View all issues with NAD Concepts status.
Discussion:
Addresses UK 214
raw_storage_iterator needs constraining as an iterator adaptor to be safely used in constrained templates
[ Summit: ]
We look forward to a paper on this topic. We recommend no action until a paper is available.
[ Post Summit Alisdair provided wording and rationale. ]
Proposed resolution:
20.8 [memory] p2
Update the synopsis for <memory>
// 20.7.8, raw storage iterator: template <classForwardIterator OutputIterator,classObjectType T> requires OutputIterator< OutIter, T > class raw_storage_iterator; template <ForwardIterator OutIter, ObjectType T> requires OutputIterator< OutIter, T > concept_map Iterator<raw_storage_iterator< OutIter, T > > { }
20.8.7 [storage.iterator] p1
Replace class template definition with:
namespace std {
template <class ForwardIterator OutputIterator, class ObjectType T>
requires OutputIterator< OutIter, T >
class raw_storage_iterator
: public iterator<output_iterator_tag,void,void,void,void> {
public:
explicit raw_storage_iterator(OutputIterator x);
raw_storage_iterator<OutputIterator,T>& operator*();
raw_storage_iterator<OutputIterator,T>& operator=(const T& element);
raw_storage_iterator<OutputIterator,T>& operator++();
raw_storage_iterator<OutputIterator,T> operator++(int);
};
template <ForwardIterator OutIter, ObjectType T>
requires OutputIterator< OutIter, T >
concept_map Iterator<raw_storage_iterator< OutIter, T > > { }
}
Rationale:
raw_storage_iterator has to adapt a ForwardIterator, rather than just an InputIterator for two reasons:
Section: 20.8.10 [specialized.algorithms] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-16
View all other issues in [specialized.algorithms].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 210
Related to 582
Specialized algorithms for memory managenment need requirements to be easily usable in constrained templates.
[ Summit: ]
We look forward to a paper on this topic. We recommend no action until a paper is available.
[ Post Summit Alisdair provided wording. ]
[ Post Summit: ]
Daniel adds:
- I suggest Size should require IntegralLike and not UnsignedIntegralLike, because otherwise simple int-literals could not be provided as arguments and it would conflict with other algorithms that only require IntegralLike.
The current for-loop-test relies on evaluation in boolean context which is not provided by ArithmeticLike and it's refinements. I propose to change the corresponding for-loop-headers to:
- for uninitialized_copy_n: for ( ; n > Size(0); ++result, ++first, --n) {
- for uninitialized_fill_n: for (; n > Size(0); ++first, --n) {
Alisdair adds:
For the record I agree with Daniel's suggestion.
Proposed resolution:
20.8 [memory] p2
Update the synopsis for <memory>
template <classInputIterator InIter,class ForwardIteratorOutputIterator<auto, InIter::reference> OutIter> requires ForwardIterator<OutIter>ForwardIteratorOutIter uninitialized_copy(InputIteratorInIter first,InputIteratorInIter last,ForwardIteratorOutIter result); template <classInputIterator InIter,classIntegralLike Size,class ForwardIteratorOutputIterator<auto, InIter::reference> OutIter> requires ForwardIterator<OutIter>ForwardIteratorOutIter uninitialized_copy_n(InputIteratorInIter first, Size n,ForwardIteratorOutIter result); template <classForwardIterator Iter,classObjectType T> requires Constructible< Iter::value_type, const T& > void uninitialized_fill(ForwardIteratorIter first,ForwardIteratorIter last, const T& x); template <classForwardIterator Iter,classIntegralLike Size,classObjectType T> requires Constructible< Iter::value_type, const T& > void uninitialized_fill_n(ForwardIteratorIter first, Size n, const T& x);
Update as follows:
uninitialized_copy 20.8.10.1 [uninitialized.copy]
template <classInputIterator InIter,class ForwardIteratorOutputIterator<auto, InIter::reference> OutIter> requires ForwardIterator<OutIter>ForwardIteratorOutIter uninitialized_copy(InputIteratorInIter first,InputIteratorInIter last,ForwardIteratorOutIter result);-1- Effects:
for (; first != last; ++result, ++first) { new (static_cast<void*>(&*result))typename iterator_traits<ForwardIterator>OutIter::value_type(*first); }-2- Returns: result
template <classInputIterator InIter,classIntegralLike Size,class ForwardIteratorOutputIterator<auto, InIter::reference> OutIter> requires ForwardIterator<OutIter>ForwardIteratorOutIter uninitialized_copy_n(InputIteratorInIter first, Size n,ForwardIteratorOutIter result);-3- Effects:
for ( ; n > Size(0); ++result, ++first, --n) { new (static_cast<void*>(&*result))typename iterator_traits<ForwardIterator>OutIter::value_type(*first); }-4- Returns: result
uninitialized_fill 20.8.10.2 [uninitialized.fill]
template <classForwardIterator Iter,classObjectType T> requires Constructible< Iter::value_type, const T& > void uninitialized_fill(ForwardIteratorIter first,ForwardIteratorIter last, const T& x);-1- Effects:
for (; first != last; ++first) { new ( static_cast<void*>( &*first) )typename iterator_traits<ForwardIterator>Iter::value_type(x); }
uninitialized_fill_n 20.8.10.3 [uninitialized.fill.n]
template <classForwardIterator Iter,classIntegralLike Size,classObjectType T> requires Constructible< Iter::value_type, const T& > void uninitialized_fill_n(ForwardIteratorIter first, Size n, const T& x);-1- Effects:
for (; n--> Size(0); ++first, --n) { new ( static_cast<void*>( &*first) )typename iterator_traits<ForwardIterator>Iter::value_type(x); }
Section: 20.9 [time] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-16
View all other issues in [time].
View all issues with NAD Concepts status.
Discussion:
Addresses JP 45
Rep, Period, Clock and Duration don't correspond to concept.
template <class Rep, class Period = ratio<1>> class duration; template <class Clock, class Duration = typename Clock::duration> class time_point;
Make concept for Rep, Period, Clock and Duration. Fix 20.9 [time] and wait_until and wait_for's template parameter at 30 [thread].
[ Summit: ]
We agree that this section needs concepts. We look forward to a paper on this topic. We recommend no action until a paper is available.
Proposed resolution:
Section: 23.2.3 [sequence.reqmts] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-15
View all other issues in [sequence.reqmts].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 231
p9-p11 are redundant now that Concepts define what it means to be an Iterator and guide overload resolution accordingly.
[ Summit: ]
Agree with issue and change to 23.2.3 [sequence.reqmts]. The changes required to 21 [strings] will be part of the general concept support for that clause.
Proposed resolution:
Strike 23.2.3 [sequence.reqmts]p9-11. Make sure std::basic_string has constraints similar to std::vector to meet this old guarantee.
Section: 26.5 [rand] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-15
View all other issues in [rand].
View all issues with NAD Concepts status.
Discussion:
The RandomNumberEngineAdaptor concept breaks precedent in the way the library has been specified by grouping requirements into a concept that is never actually used in the library.
This is undoubtedly a very helpful device for documentation, but we are not comfortable with the precedent - especially as we have rejected national body comments on the same grounds.
Suggest either removing the concept, or providing an algorithm/type that requires this concept in their definition (such as a factory function to create new engines).
The preference is to create a single new algorithm and retain the value of the existing documentation.
[ Batavia (2009-05): ]
Walter points out that it is unlikely that any algorithm would ever require this concept, but that the concept nonetheless is useful as documentation, and (via concept maps) as a means of checking specific adapters.
Alisdair disagrees as to the concept's value as documentation.
Marc points out that the RandomNumberDistribution is also a concept not used elsewhere in the Standard.
Pete agrees that a policy of not inventing concepts that aren't used in the Standard is a good starting point, but should not be used as a criterion for rejecting a concept.
Move to Open.
Proposed resolution:
Section: 23.2.3 [sequence.reqmts] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-13
View all other issues in [sequence.reqmts].
View all issues with NAD Editorial status.
Discussion:
Sequence containers 23.2.3 [sequence.reqmts]:
The return value of new calls added to table 83 are not specified.
[ Batavia (2009-05): ]
We agree with the proposed resolution.
Move to NAD Editorial.
Proposed resolution:
Add after p6 23.2.3 [sequence.reqmts]:
-6- ...
The iterator returned from a.insert(p,rv) points to the copy of rv inserted into a.
The iterator returned from a.emplace(p, args) points to the new element constructed from args inserted into a.
Section: 20.7.15.2 [func.wrap.func] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2009-03-13 Last modified: 2009-07-16
View all other issues in [func.wrap.func].
View all issues with NAD Concepts status.
Discussion:
Due to a deliberate core language decision, the earlier called "foundation" concept std::FunctionType had been removed in N2773 shortly before the first "conceptualized" version of the WP (N2798) had been prepared. This caused a break of the library, which already used this concept in the adapted definition of std::function (20.7 [function.objects]/2, header <functional> synopsis and 20.7.15.2 [func.wrap.func]).
A simple fix would be to either (a) make std::function's primary template unconstrained or to (b) add constraints based on existing (support) concepts. A more advanced fix would (c) introduce a new library concept.
The big disadvantage of (a) is, that users can define templates which cause compiler errors during instantiation time because of under-constrainedness and would thus violate the basic advantage of constrained code.
For (b), the ideal constraints for std::function's template parameter would be one which excludes everything else but the single provided partial specialization that matches every "free function" type (i.e. any function type w/o cv-qualifier-seq and w/o ref-qualifier). Expressing such a type as as single requirement would be written as
template<typename T>
requires ReferentType<T> // Eliminate cv void and function types with cv-qual-seq
// or ref-qual (depending on core issue #749)
&& PointeeType<T> // Eliminate reference types
&& !ObjectType<T> // Eliminate object types
Just for completeness approach (c), which would make sense, if the library has more reasons to constrain for free function types:
auto concept FreeFunctionType<typename T>
: ReferentType<T>, PointeeType<T>, MemberPointeeType<T>
{
requires !ObjectType<T>;
}
I mention that approach because I expect that free function types belong to the most natural type categories for every days coders. Potential candidates in the library are addressof and class template packaged_task.
[ Batavia (2009-05): ]
Alisdair would prefer to have a core-supported FunctionType concept in order that any future changes be automatically correct without need for a library solution to catch up; he points to type traits as a precedent. Further, he believes that a published concept can't in the future be changed.
Bill feels this category of entity would change sufficiently slowly that he would be willing to take the risk.
Of the discussed solutions, we tend toward option (c). We like the idea of having a complete taxonomy of native types, and perhaps erred in trimming the set.
We would like to have this issue reviewed by Core and would like their feedback. Move to Open.
Proposed resolution:
Change in 20.7 [function.objects]/2, Header <functional> synopsis:
// 20.6.16 polymorphic function wrappers: class bad_function_call; template<FunctionTypeReferentType F> requires PointeeType<F> && !ObjectType<F> class function; // undefined
Change in 20.7.15.2 [func.wrap.func]:
namespace std {
template<FunctionTypeReferentType F>
requires PointeeType<F> && !ObjectType<F>
class function; // undefined
Section: 17.5.2.1.4.1 [byte.strings] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2009-03-13 Last modified: 2009-07-13
View all issues with NAD Editorial status.
Discussion:
Definition of null-terminated sequences allow for embedded nulls. This is surprising, and probably not supportable with the intended use cases.
[ Batavia (2009-05): ]
We agree with the issue, but believe this can be handled editorially. Move to NAD Editorial.
Proposed resolution:
Section: 20.3.4 [pair.astuple] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2009-03-13 Last modified: 2009-07-13
View all issues with NAD Editorial status.
Discussion:
The definition of get implies that get must return the second element if given a negative integer.
[ Batavia (2009-05): ]
Move to NAD Editorial.
Proposed resolution:
20.3.4 [pair.astuple] p5:
template<intsize_t I, class T1, class T2> requires True<(I < 2)> const P& get(const pair<T1, T2>&);
Section: X [iterator.backward] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-15 Last modified: 2009-07-16
View all issues with NAD Concepts status.
Discussion:
Which header must a user #include to obtain the library-supplied concept_maps declared in this paragraph?
This is important information, as existing user code will break if this header is not included, and we should make a point of mandating this header is #include-d by library headers likely to make use of it, notably <algorithm>. See issue 1001 for more details.
[ Batavia (2009-05): ]
We agree with the direction of the proposed resolution. Move to Tentatively Ready.
[ 2009-07 Frankfurt ]
We believe this is NAD Concepts, but this needs to be reviewed against the post-remove-concepts draft.
Proposed resolution:
Change [depr.lib.iterator.primitives], Iterator primitives, as indicated:
To simplify the use of iterators and provide backward compatibility with previous C++ Standard Libraries, the library provides several classes and functions. Unless otherwise specified, these classes and functions shall be defined in header <iterator>.
Change X [iterator.backward], Iterator backward compatibility, as indicated:
The library provides concept maps that allow iterators specified with iterator_traits to interoperate with algorithms that require iterator concepts. These concept maps shall be defined in the same header that defines the iterator. [Example:
Section: 26.7 [numeric.ops] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-17 Last modified: 2009-07-14
View all issues with NAD Concepts status.
Discussion:
One of the motivating examples for introducing requirements-aliases was to simplify the wording of the inner_product requirements. As the paper adopting the feature and constrained wording for the library went through in the same meeting, it was not possible to make the change at the time. The simpler form should be adopted now though. Similarly, most the other numerical algorithms can benefit from a minor cleanup.
Note that in each case, the second more generalised form of the algorithm does not benefit, as there are already named constraints supplied by the template type parameters.
[ 2009-05-02 Daniel adds: ]
one part of the suggested resolution suggests the removal of the MoveConstructible<T> requirement from inner_product. According to 26.7.2 [inner.product]
Computes its result by initializing the accumulator acc with the initial value initthis step requires at least MoveConstructible.
Therefore I strongly suggest to take this removal back (Note also that the corresponding overload with a functor argument still has the same MoveConstructible<T> requirement).
[ Batavia (2009-05): ]
We agree with the proposed resolution as amended by Daniel's suggestion to restore MoveConstructible, reflected in the updated proposed resolution below.
Move to Tentatively Ready.
Proposed resolution:
Change in 26.7 [numeric.ops] and 26.7.1 [accumulate]:
template <InputIterator Iter, MoveConstructible T>
requires add = HasPlus<T, Iter::reference>
&& HasAssign<T, HasPlus<T, Iter::reference> add::result_type>
T accumulate(Iter first, Iter last, T init);
Change in 26.7 [numeric.ops] and 26.7.2 [inner.product]:
template <InputIterator Iter1, InputIterator Iter2, MoveConstructible T>
requires mult = HasMultiply<Iter1::reference, Iter2::reference>
&& add = HasPlus<T, HasMultiply<Iter1::reference, Iter2::reference> mult::result_type>
&& HasAssign<
T,
HasPlus<T,
HasMultiply<Iter1::reference, Iter2::reference>::result_type> add::result_type>
T inner_product(Iter1 first1, Iter1 last1, Iter2 first2, T init);
Change in 26.7 [numeric.ops] and 26.7.3 [partial.sum]:
template <InputIterator InIter, OutputIterator<auto, const InIter::value_type&> OutIter>
requires add = HasPlus<InIter::value_type, InIter::reference>
&& HasAssign<InIter::value_type,
HasPlus<InIter::value_type, InIter::reference> add::result_type>
&& Constructible<InIter::value_type, InIter::reference>
OutIter partial_sum(InIter first, InIter last, OutIter result);
Change in 26.7 [numeric.ops] and 26.7.4 [adjacent.difference]:
template <InputIterator InIter, OutputIterator<auto, const InIter::value_type&> OutIter>
requires sub = HasMinus<InIter::value_type, InIter::value_type>
&& Constructible<InIter::value_type, InIter::reference>
&& OutputIterator<OutIter, HasMinus<InIter::value_type, InIter::value_type> sub::result_type>
&& MoveAssignable<InIter::value_type>
OutIter adjacent_difference(InIter first, InIter last, OutIter result);
Section: 20.7.16 [unord.hash] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-19 Last modified: 2009-07-16
View other active issues in [unord.hash].
View all other issues in [unord.hash].
View all issues with NAD Concepts status.
Discussion:
Is std::hash a constrained template or not?
According to Class template hash 20.7.16 [unord.hash], the definition is:
template <class T>
struct hash : public std::unary_function<T, std::size_t> {
std::size_t operator()(T val) const;
};
And so unconstrained.
According to the <functional> synopsis in p2 Function objects 20.7 [function.objects] the template is declared as:
template <ReferentType T> struct hash;
which would make hash a constrained template.
[ 2009-03-22 Daniel provided wording. ]
[ Batavia (2009-05): ]
Alisdair is not certain that Daniel's proposed resolution is sufficient, and recommends we leave the hash template unconstrained for now.
Recommend that the Project Editor make the constrained declaration consistent with the definition in order to make the Working Paper internally consistent, and that the issue then be revisited.
Move to Open.
Proposed resolution:
[To the editor: This resolution is merge-compatible to the resolution of 1078]
In 20.7 [function.objects]/2, header <functional> synopsis, change as indicated:
// 20.6.17, hash function base template: template <ReferentType T> struct hash; // undefined
In 20.7.16 [unord.hash]/1 change as indicated:
namespace std {
template <class T>
struct hash : public std::unary_function<T, std::size_t> {
std::size_t operator()(T val) const;
};
template <ReferentType T> struct hash; // undefined
}
In 20.7.16 [unord.hash]/2 change as indicated:
-2- For all library-provided specializations, the template instantiation hash<T> shall provide a public operator() with return type std::size_t to satisfy the concept requirement Callable<const hash<T>, const T&>. If T is an object type or reference to object, hash<T> shall be publicly derived from std::unary_function<T, std::size_t>. The return value of operator() is unspecified, except that equal arguments shall yield the same result. operator() shall not throw exceptions.
In 18.7 [support.rtti]/1, header <typeinfo> synopsis change as indicated:
namespace std {
class type_info;
class type_index;
template <classReferentType T> struct hash;
Section: 20.8.4 [allocator.element.concepts] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-03-19 Last modified: 2009-07-13
View all issues with NAD Concepts status.
Discussion:
p7 Allocator-related element concepts 20.8.4 [allocator.element.concepts]
The changes to the AllocatableElement concept mean this concept_map specialization no longer matches the original concept:
template <Allocator Alloc, class T, class ... Args>
requires HasConstructor<T, Args...>
concept_map AllocatableElement<Alloc, T, Args&&...> {
void construct_element(Alloc& a, T* t, Args&&... args) {
Alloc::rebind<T>(a).construct(t, forward(args)...);
}
}
[ 2009-03-23 Pablo adds: ]
Actually, this is incorrect, N2840 says. "In section 20.8.4 [allocator.element.concepts] paragraph 8, modify the definition of the AllocatableElement concept and eliminate the related concept map:" but then neglects to include the red-lined text of the concept map that was to be eliminated. Pete also missed this, but I caught it he asked me to review his edits. Pete's updated WP removes the concept map entirely, which was the original intent. The issue is, therefore, moot. Note, as per my presentation of N2840 in summit, construct() no longer has a default implementation. This regrettable fact was deemed (by David Abrahams, Doug, and myself) to be preferable to the complexity of providing a default implementation that would not under-constrain a more restrictive allocator (like the scoped allocators).
[ 2009-05-01 Daniel adds: ]
it seems to me that #1074 should be resolved as a NAD, because the current WP has already removed the previous AllocatableElement concept map. It introduced auto concept AllocatableElement instead, but as of 20.8.4 [allocator.element.concepts]/7 this guy contains now
requires FreeStoreAllocatable<T>; void Alloc::construct(T*, Args&&...);
[ Batavia (2009-05): ]
The affected code is no longer part of the Working Draft.
Move to NAD.
Proposed resolution:
Change 20.8.4 [allocator.element.concepts]:
template <Allocator Alloc, class T, class ... Args>
requires HasConstructor<T, Args...>
concept_map AllocatableElement<Alloc, T, Args&&...> {
void construct_element(Alloc& a, T* t, Args&&... args) {
Alloc::rebind<T>(a).construct(t, forward(args)...);
}
}
Section: 20.5.2 [tuple.tuple] Status: NAD Editorial Submitter: Pete Becker Opened: 2009-03-20 Last modified: 2009-07-13
View all other issues in [tuple.tuple].
View all issues with NAD Editorial status.
Discussion:
Class template tuple 20.5.2 [tuple.tuple]:
template <class... UTypes> requires Constructible<Types, const UTypes&>... template <class... UTypes> requires Constructible<Types, RvalueOf<UTypes>::type>...
Somebody needs to look at this and say what it should be.
[ 2009-03-21 Daniel provided wording. ]
[ Batavia (2009-05): ]
The resolution looks correct; move to NAD Editorial.
Proposed resolution:
In 20.5.2 [tuple.tuple], class tuple, change as indicated:
template <class... UTypes> requires Constructible<Types, const UTypes&>... tuple(const pair<UTypes...>&); template <class... UTypes> requires Constructible<Types, RvalueOf<UTypes>::type>... tuple(pair<UTypes...>&&);
[NB.: The corresponding prototypes do already exist in 20.5.2.1 [tuple.cnstr]/7+8]
Section: 20.11 [type.index] Status: NAD Concepts Submitter: Doug Gregor Opened: 2009-03-20 Last modified: 2009-07-16
View all issues with NAD Concepts status.
Discussion:
Addresses DE 17
DE-17:
The class type_index should be removed; it provides no additional functionality beyond providing appropriate concept maps.
[ 2009-03-31 Peter adds: ]
It is not true, in principle, that std::type_index provides no utility compared to bare std::type_info*.
std::type_index can avoid the lifetime issues with type_info when the DLL that has produced the type_info object is unloaded. A raw type_info* does not, and cannot, provide any protection in this case. A type_index can (if the implementor so chooses) because it can wrap a smart (counted or even cloning) pointer to the type_info data that is needed for name() and before() to work.
Proposed resolution:
Modify the header <typeinfo> synopsis in 18.7 [support.rtti]p1 as follows:
namespace std {
class type_info;
class type_index;
template <class T> struct hash;
template<> struct hash<type_indexconst type_info *> : public std::unary_function<type_indexconst type_info *, size_t> {
size_t operator()(type_indexconst type_info * indext) const;
};
concept_map LessThanComparable<const type_info *> see below
class bad_cast;
class bad_typeid;
}
Add the following new subsection
18.7.1.1 Template specialization
hash<const type_info *>[type.info.hash]size_t operator()(const type_info *x) const;
- Returns:
x->hash_code()
Add the following new subsection
18.7.1.2
type_infoconcept map [type.info.concepts]concept_map LessThanComparable<const type_info *> { bool operator<(const type_info *x, const type_info *y) { return x->before(*y); } bool operator<=(const type_info *x, const type_info *y) { return !y->before(*x); } bool operator>(const type_info *x, const type_info *y) { return y->before(*x); } bool operator>=(const type_info *x, const type_info *y) { return !x->before(*y); } }
- Note: provides a well-defined ordering among
type_info constpointers, which makes such pointers usable in associative containers (23.4).
Remove section 20.11 [type.index]
Section: X [concept.arithmetic] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2009-03-21 Last modified: 2009-07-15
View all issues with NAD Concepts status.
Discussion:
Astonishingly, the current concept ArithmeticLike as specified in X [concept.arithmetic] does not provide explicit conversion to bool although this is a common property of arithmetic types (4.12 [conv.bool]). Recent proposals that introduced such types (integers of arbitrary precision, n2143, decimals n2732 indirectly via conversion to long long) also took care of such a feature.
Adding such an explicit conversion associated function would also partly solve a currently invalid effects clause in library, which bases on this property, 24.2.5 [random.access.iterators]/2:
{ difference_type m = n;
if (m >= 0) while (m--) ++r;
else while (m++) --r;
return r; }
Both while-loops take advantage of a contextual conversion to bool (Another problem is that the >= comparison uses the no longer supported existing implicit conversion from int to IntegralLike).
Original proposed resolution:In X [concept.arithmetic], add to the list of less refined concepts one further concept:
concept ArithmeticLike<typename T>
: Regular<T>, LessThanComparable<T>, HasUnaryPlus<T>, HasNegate<T>,
HasPlus<T, T>, HasMinus<T, T>, HasMultiply<T, T>, HasDivide<T, T>,
HasPreincrement<T>, HasPostincrement<T>, HasPredecrement<T>,
HasPostdecrement<T>,
HasPlusAssign<T, const T&>, HasMinusAssign<T, const T&>,
HasMultiplyAssign<T, const T&>,
HasDivideAssign<T, const T&>, ExplicitlyConvertible<T, bool> {
In 24.2.5 [random.access.iterators]/2 change the current effects clause as indicated [The proposed insertion fixes the problem that the previous implicit construction from integrals has been changed to an explicit constructor]:
{ difference_type m = n;
if (m >= difference_type(0)) while (m--) ++r;
else while (m++) --r;
return r; }
[ Batavia (2009-05): ]
We agree that arithmetic types ought be convertible to bool, and we therefore agree with the proposed resolution's paragraph 1.
We do not agree that the cited effects clause is invalid, as it expresses intent rather than specific code.
Move to Review, pending input from concepts experts.
Proposed resolution:
In X [concept.arithmetic], add to the list of less refined concepts one further concept:
concept ArithmeticLike<typename T>
: Regular<T>, LessThanComparable<T>, HasUnaryPlus<T>, HasNegate<T>,
HasPlus<T, T>, HasMinus<T, T>, HasMultiply<T, T>, HasDivide<T, T>,
HasPreincrement<T>, HasPostincrement<T>, HasPredecrement<T>,
HasPostdecrement<T>,
HasPlusAssign<T, const T&>, HasMinusAssign<T, const T&>,
HasMultiplyAssign<T, const T&>,
HasDivideAssign<T, const T&>, ExplicitlyConvertible<T, bool> {
Section: 21 [strings] Status: NAD Concepts Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2009-07-15
View all other issues in [strings].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 216, JP 46, JP 48
All the containers use concepts for their iterator usage, exect for basic_string. This needs fixing.
Use concepts for iterator template parameters throughout the chapter.
[ Summit: ]
NB comments to be handled by Dave Abrahams and Howard Hinnant with advice from PJP: UK216 (which duplicates) JP46, JP48. JP46 supplies extensive proposed wording; start there.
Proposed resolution:
Section: 22 [localization] Status: NAD Concepts Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2009-07-15
View all other issues in [localization].
View all issues with NAD Concepts status.
Discussion:
Addresses JP 49
codecvt does not use concept. For example, create CodeConvert concept and change as follows.
template<CodeConvert Codecvt, class Elem = wchar_t>
class wstring_convert {
[ Summit: ]
To be handled by Howard Hinnant, Dave Abrahams, Martin Sebor, PJ Plauger.
Proposed resolution:
Section: 22 [localization] Status: NAD Concepts Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2009-07-15
View all other issues in [localization].
View all issues with NAD Concepts status.
Discussion:
Addresses JP 52, JP 53
InputIterator does not use concept.
OutputIterator does not use concept.
Comments include proposed wording.
[ Summit: ]
To be handled by Howard Hinnant, Dave Abrahams, Martin Sebor, PJ Plauger.
Proposed resolution:
Section: 24.2.3 [forward.iterators] Status: NAD Concepts Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2009-07-16
View all other issues in [forward.iterators].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 250
A default implementation should be supplied for the post-increment operator to simplify implementation of iterators by users.
Copy the Effects clause into the concept description as the default implementation. Assumes a default value for postincrement_result
[ Summit: ]
Howard will open an issue.
[ 2009-06-07 Daniel adds: ]
This issue cannot currently be resolved as suggested, because that would render auto-detection of the return type postincrement_result invalid, see [concept.map.assoc]/4+5. The best fix would be to add a default type to that associated type, but unfortunately any default type will prevent auto-deduction of types of associated functions as quoted above. A corresponding core issue is in preparation.
Proposed resolution:
[ This wording assumes the acceptance of UK 251 / 1009. Both wordings change the same paragraphs. ]
Change 24.2.3 [forward.iterators]:
concept ForwardIterator<typename X> : InputIterator<X>, Regular<X> {
MoveConstructible postincrement_result;
requires HasDereference<postincrement_result>
&& Convertible<HasDereference<postincrement_result>::result_type, const value_type&>;
postincrement_result operator++(X& r, int); {
X tmp = r;
++r;
return tmp;
}
axiom MultiPass(X a, X b) {
if (a == b) *a == *b;
if (a == b) ++a == ++b;
}
}
Section: 24.2.4 [bidirectional.iterators] Status: NAD Concepts Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2009-07-16
View all other issues in [bidirectional.iterators].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 258
A default implementation should be supplied for the post-decrement operator to simplify implementation of iterators by users.
Copy the Effects clause into the concept description as the default implementation. Assumes a default value for postincrement_result
[ Summit: ]
Howard will open an issue.
[ 2009-06-07 Daniel adds: ]
This issue cannot currently be resolved as suggested, because that would render auto-detection of the return type postdecrement_result invalid, see 1084.
Proposed resolution:
Change 24.2.4 [bidirectional.iterators]:
concept BidirectionalIterator<typename X> : ForwardIterator<X> {
MoveConstructible postdecrement_result;
requires HasDereference<postdecrement_result>
&& Convertible<HasDereference<postdecrement_result>::result_type, const value_type&>
&& Convertible<postdecrement_result, const X&>;
X& operator--(X&);
postdecrement_result operator--(X& r, int); {
X tmp = r;
--r;
return tmp;
}
}
Section: 24.6 [stream.iterators] Status: NAD Concepts Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2009-07-15
View all issues with NAD Concepts status.
Discussion:
Addresses UK 284
The stream iterators need constraining with concepts/requrires clauses.
[ Summit: ]
We agree. To be handled by Howard, Martin and PJ.
Proposed resolution:
Section: 25.3.5 [alg.replace] Status: NAD Concepts Submitter: Howard Hinnant Opened: 2009-03-22 Last modified: 2009-07-15
View all other issues in [alg.replace].
View all issues with NAD Concepts status.
Discussion:
Addresses UK 301
replace and replace_if have the requirement: OutputIterator<Iter, Iter::reference> Which implies they need to copy some values in the range the algorithm is iterating over. This is not however the case, the only thing that happens is const T&s might be copied over existing elements (hence the OutputIterator<Iter, const T&>.
Remove OutputIterator<Iter, Iter::reference> from replace and replace_if.
[ Summit: ]
We agree. To be handled by Howard.
Proposed resolution:
Change in [algorithms.syn] and 25.3.5 [alg.replace]:
template<ForwardIterator Iter, class T> requiresOutputIterator<Iter, Iter::reference> &&OutputIterator<Iter, const T&> && HasEqualTo<Iter::value_type, T> void replace(Iter first, Iter last, const T& old_value, const T& new_value); template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred, class T> requiresOutputIterator<Iter, Iter::reference> &&OutputIterator<Iter, const T&> && CopyConstructible<Pred> void replace_if(Iter first, Iter last, Pred pred, const T& new_value);
Section: 20.6.3 [meta.help] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2009-03-22 Last modified: 2009-07-15
View other active issues in [meta.help].
View all other issues in [meta.help].
View all issues with NAD Concepts status.
Discussion:
A first step to change the type traits predicates to constrained templates is to constrain their common base template integral_constant. This can be done, without enforcing depending classes to be constrained as well, but not vice versa without brute force late_check usages. The following proposed resolution depends on the resolution of LWG issue 1019.
[ Batavia (2009-05): ]
Move to Open, pending a paper that looks at constraints for the entirety of the type traits and their relationship to the foundation concepts. We recommend this be deferred until after the next Committee Draft is issued.
Proposed resolution:
In 20.6.2 [meta.type.synop], Header <type_traits> synopsis change as indicated:
namespace std {
// 20.5.3, helper class:
template <classIntegralConstantExpressionType T, T v> struct integral_constant;
In 20.6.3 [meta.help] change as indicated:
template <classIntegralConstantExpressionType T, T v> struct integral_constant { static constexpr T value = v; typedef T value_type; typedef integral_constant<T,v> type; constexpr operator value_type() { return value; } };
Section: 17 [library] Status: NAD Concepts Submitter: David Abrahams Opened: 2009-03-21 Last modified: 2009-07-16
View other active issues in [library].
View all other issues in [library].
View all issues with NAD Concepts status.
Discussion:
TODO: Look at all cases of unconstrained rvalue ref parameters and check that concept req'ts work when T deduced as reference.
We found some instances where that was not done correctly and we figure the possibility of deducing T to be an lvalue reference was probably overlooked elsewhere.
[ Batavia (2009-05): ]
Move to Open, pending proposed wording from Dave for further review.
Proposed resolution:
Section: 25.3.9 [alg.unique] Status: NAD Editorial Submitter: Howard Hinnant Opened: 2009-04-25 Last modified: 2009-07-13
View all other issues in [alg.unique].
View all issues with NAD Editorial status.
Discussion:
From Message c++std-core-14160 Howard wrote:
It was the intent of the rvalue reference proposal for unique to only require MoveAssignable: N1860.
And Pete replied:
That was overridden by the subsequent changes made for concepts in N2573, which reimposed the C++03 requirements.
My impression is that this overwrite was a simple (unintentional) mistake. Wording below to correct it.
[ Batavia (2009-05): ]
Howard notes this issue resolves a discrepancy between the synopsis and the description.
Move to NAD Editorial.
Proposed resolution:
Change 25.3.9 [alg.unique]:
template<ForwardIterator Iter>
requires OutputIterator<Iter, RvalueOf<Iter::reference>::type>
&& EqualityComparable<Iter::value_type>
Iter unique(Iter first, Iter last);
template<ForwardIterator Iter, EquivalenceRelation<auto, Iter::value_type> Pred>
requires OutputIterator<Iter, RvalueOf<Iter::reference>::type>
&& CopyConstructible<Pred>
Iter unique(Iter first, Iter last, Pred pred);
Note that the synopsis in [algorithms.syn] is already correct.
Section: X [iterator.concepts.range] Status: NAD Concepts Submitter: David Abrahams Opened: 2009-04-23 Last modified: 2009-07-15
View all issues with NAD Concepts status.
Discussion:
[ 2009-04-26 Herb adds: ]
Here's a common example: We have many ISV customers who have built lots of in-house STL-like containers. Imagine that, for the past ten years, the user has been happily using his XYZCorpContainer<T> that has begin() and end() and an iterator typedef, and indeed satisfies nearly all of Container, though maybe not quite all just like valarray. The user upgrades to a range-enabled version of a library, and now lib_algo( xyz.begin(), xyz.end()); no longer works -- compiler error.
Even though XYZCorpContainer matches the pre-conceptized version of the algorithm, and has been working for years, it appears the user has to write at least this:
template<class T> concept_map Range<XYZCorpContainer<T>> {}; template<class T> concept_map Range<const XYZCorpContainer<T>> {};Is that correct?
But he may actually have to write this as we do for initializer list:
template<class T> concept_map Range<XYZCorpContainer<T>> { typedef T* iterator; iterator begin(XYZCorpContainer<T> c) { return c.begin(); } iterator end(XYZCorpContainer<T> c) { return c.end(); } }; template<class T> concept_map Range<const XYZCorpContainer<T>> { typedef T* iterator; iterator begin(XYZCorpContainer<T> c) { return c.begin(); } iterator end(XYZCorpContainer<T> c) { return c.end(); } };
[ 2009-04-28 Alisdair adds: ]
I recommend NAD, although remain concerned about header organisation.
A user container will satisfy the MemberContainer concept, which IS auto. There is a concept_map for all MemberContainers to Container, and then a further concept_map for all Container to Range, so the stated problem is not actually true. User defined containers will automatically match the Range concept without explicitly declaring a concept_map.
The problem is that they should now provide an additional two headers, <iterator_concepts> and <container_concepts>. The only difference from making Range an auto concept would be this reduces to a single header, <iterator_concepts>.
I am strongly in favour of any resolution that tackles the issue of explicitly requiring concept headers to make these concept maps available.
[ Batavia (2009-05): ]
We observe there is a recent paper by Bjarne that overlaps this issue.
Alisdair continues to recommend NAD.
Move to Open, and recommend the issue be deferred until after the next Committee Draft is issued.
Proposed resolution:
Section: 30.6.6 [future.shared_future] Status: NAD Editorial Submitter: Thomas J. Gritzan Opened: 2009-04-03 Last modified: 2009-07-13
View other active issues in [future.shared_future].
View all other issues in [future.shared_future].
View all issues with NAD Editorial status.
Discussion:
In the shared_future class definition in 30.6.6 [future.shared_future] the move constructor that constructs a shared_future from an unique_future receives the parameter by value. In paragraph 3, the same constructor receives it as const value.
I think that is a mistake and the constructor should take a r-value reference:
shared_future(unique_future<R>&& rhs);
[ Batavia (2009-05): ]
We agree with the proposed resolution.
Move to Tentatively Ready.
[ 2009-07-05 Daniel notes: ]
The proposed change has already been incorported into the current working draft N2914.
Proposed resolution:
Change the synopsis in 30.6.6 [future.shared_future]:
shared_future(unique_future<R>&& rhs);
Change the definition of the constructor in 30.6.6 [future.shared_future]:
shared_future(constunique_future<R>&& rhs);
Section: 25.4.5.1 [includes] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-04-28 Last modified: 2009-07-13
View all other issues in [includes].
View all issues with NAD Concepts status.
Discussion:
All the set operation algorithms require a CopyConstructible predicate, with the exception of std::includes. This looks like a typo as much as anything, given the general library requirement that predicates are copy constructible, and wording style of other set-like operations.
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to NAD Editorial.
Proposed resolution:
Change [algorithms.syn] and 25.4.5.1 [includes]:
template<InputIterator Iter1, InputIterator Iter2,
typename CopyConstructible Compare>
requires Predicate<Compare, Iter1::value_type, Iter2::value_type>
&& Predicate<Compare, Iter2::value_type, Iter1::value_type>
bool includes(Iter1 first1, Iter1 last1,
Iter2 first2, Iter2 last2,
Compare comp);
Section: 23.4 [associative] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-04-29 Last modified: 2009-07-16
View all other issues in [associative].
View all issues with NAD Concepts status.
Discussion:
According to table 87 (n2857) the expression X::key_equal for an unordered container shall return a value of type Pred, where Pred is an equivalence relation.
However, all 4 containers constrain Pred to be merely a Predicate, and not EquivalenceRelation.
[ Batavia (2009-05): ]
We agree with the proposed resolution.
Move to Review.
Proposed resolution:
For ordered containers, replace
Predicate<auto, Key, Key> Compare = less<Key>
with
StrictWeakOrder<auto, Key, Key> Compare = less<Key>
For unordered containers, replace
Predicate<auto, Key, Key> Compare = less<Key>
with
EquivalenceRelation<auto, Key, Key> Compare = less<Key>
As in the following declarations:
Associative containers 23.4 [associative]
1 Headers <map> and <set>:
Header <map> synopsis
namespace std { template <ValueType Key, ValueType T,PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>, Allocator Alloc = allocator<pair<<b>const Key, T> > > requires NothrowDestructible<Key> && NothrowDestructible<T> && CopyConstructible<Compare> && AllocatableElement<Alloc, Compare, const Compare&> && AllocatableElement<Alloc, Compare, Compare&&> class map; ... template <ValueType Key, ValueType T,PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>, Allocator Alloc = allocator<pair<<b>const Key, T> > > requires NothrowDestructible<Key> && NothrowDestructible<T> && CopyConstructible<Compare> && AllocatableElement<Alloc, Compare, const Compare&> && AllocatableElement<Alloc, Compare, Compare&&> class multimap; ... }Header <set> synopsis
namespace std { template <ValueType Key,PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>, Allocator Alloc = allocator<Key> > requires NothrowDestructible<Key> && CopyConstructible<Compare> && AllocatableElement<Alloc, Compare, const Compare&> && AllocatableElement<Alloc, Compare, Compare&&> class set; ... template <ValueType Key,PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>, Allocator Alloc = allocator<Key> > requires NothrowDestructible<Key> && CopyConstructible<Compare> && AllocatableElement<Alloc, Compare, const Compare&> && AllocatableElement<Alloc, Compare, Compare&&> class multiset; ... }23.4.1p2 Class template map [map]
namespace std { template <ValueType Key, ValueType T,PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>, Allocator Alloc = allocator<pair<<b>const Key, T> > > requires NothrowDestructible<Key> && NothrowDestructible<T> && CopyConstructible<Compare> && AllocatableElement<Alloc, Compare, const Compare&> && AllocatableElement<Alloc, Compare, Compare&&> class map { ... }; }23.4.2p2 Class template multimap [multimap]
namespace std { template <ValueType Key, ValueType T,PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>, Allocator Alloc = allocator<pair<<b>const Key, T> > > requires NothrowDestructible<Key> && NothrowDestructible<T> && CopyConstructible<Compare> && AllocatableElement<Alloc, Compare, const Compare&> && AllocatableElement<Alloc, Compare, Compare&&> class multimap { ... }; }23.4.3p2 Class template set [set]
namespace std { template <ValueType Key,PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>, Allocator Alloc = allocator<Key> > requires NothrowDestructible<Key> && CopyConstructible<Compare> && AllocatableElement<Alloc, Compare, const Compare&> && AllocatableElement<Alloc, Compare, Compare&&> class set { ... }; }23.4.4p2 Class template multiset [multiset]
namespace std { template <ValueType Key,PredicateStrictWeakOrder<auto, Key, Key> Compare = less<Key>, Allocator Alloc = allocator<Key> > requires NothrowDestructible<Key> && CopyConstructible<Compare> && AllocatableElement<Alloc, Compare, const Compare&> && AllocatableElement<Alloc, Compare, Compare&&> class multiset { ... }; }23.5 Unordered associative containers [unord]
1 Headers <unordered_map> and <unordered_set>:
Header <unordered_map> synopsis
namespace std { // 23.5.1, class template unordered_map: template <ValueType Key, ValueType T, Callable<auto, const Key&> Hash = hash<Key>,PredicateEquivalenceRelation<auto, Key, Key> Pred = equal_to<Key>, Allocator Alloc = allocator<pair<<b>const Key, T> > > requires NothrowDestructible<Key> && NothrowDestructible<T> && SameType<Hash::result_type, size_t> && CopyConstructible<Hash> && CopyConstructible<Pred> && AllocatableElement<Alloc, Pred, const Pred&> && AllocatableElement<Alloc, Pred, Pred&&> && AllocatableElement<Alloc, Hash, const Hash&> && AllocatableElement<Alloc, Hash, Hash&&> class unordered_map; // 23.5.2, class template unordered_multimap: template <ValueType Key, ValueType T, Callable<auto, const Key&> Hash = hash<Key>,PredicateEquivalenceRelation<auto, Key, Key> Pred = equal_to<Key>, Allocator Alloc = allocator<pair<<b>const Key, T> > > requires NothrowDestructible<Key> && NothrowDestructible<T> && SameType<Hash::result_type, size_t> && CopyConstructible<Hash> && CopyConstructible<Pred> && AllocatableElement<Alloc, Pred, const Pred&> && AllocatableElement<Alloc, Pred, Pred&&> && AllocatableElement<Alloc, Hash, const Hash&> && AllocatableElement<Alloc, Hash, Hash&&> class unordered_multimap; ... }Header <unordered_set> synopsis
namespace std { // 23.5.3, class template unordered_set: template <ValueType Value, Callable<auto, const Value&> Hash = hash<Value>,PredicateEquivalenceRelation<auto, Value, Value> class Pred = equal_to<Value>, Allocator Alloc = allocator<Value> > requires NothrowDestructible<Value> && SameType<Hash::result_type, size_t> && CopyConstructible<Hash> && CopyConstructible<Pred> && AllocatableElement<Alloc, Pred, const Pred&> && AllocatableElement<Alloc, Pred, Pred&&> && AllocatableElement<Alloc, Hash, const Hash&> && AllocatableElement<Alloc, Hash, Hash&&> class unordered_set; // 23.5.4, class template unordered_multiset: template <ValueType Value, Callable<auto, const Value&> Hash = hash<Value>,PredicateEquivalenceRelation<auto, Value, Value> class Pred = equal_to<Value>, Allocator Alloc = allocator<Value> > requires NothrowDestructible<Value> && SameType<Hash::result_type, size_t> && CopyConstructible<Hash> && CopyConstructible<Pred> && AllocatableElement<Alloc, Pred, const Pred&> && AllocatableElement<Alloc, Pred, Pred&&> && AllocatableElement<Alloc, Hash, const Hash&> && AllocatableElement<Alloc, Hash, Hash&&> class unordered_multiset; ... }23.5.1p3 Class template unordered_map [unord.map]
namespace std { template <ValueType Key, ValueType T, Callable<auto, const Key&> Hash = hash<Key>,PredicateEquivalenceRelation<auto, Key, Key> Pred = equal_to<Key>, Allocator Alloc = allocator<pair<<b>const Key, T> > > requires NothrowDestructible<Key> && NothrowDestructible<T> && SameType<Hash::result_type, size_t> && CopyConstructible<Hash> && CopyConstructible<Pred> && AllocatableElement<Alloc, Pred, const Pred&> && AllocatableElement<Alloc, Pred, Pred&&> && AllocatableElement<Alloc, Hash, const Hash&> && AllocatableElement<Alloc, Hash, Hash&&> class unordered_map { ... }; }23.5.2p3 Class template unordered_multimap [unord.multimap]
namespace std { template <ValueType Key, ValueType T, Callable<auto, const Key&> Hash = hash<Key>,PredicateEquivalenceRelation<auto, Key, Key> Pred = equal_to<Key>, Allocator Alloc = allocator<pair<<b>const Key, T> > > requires NothrowDestructible<Key> && NothrowDestructible<T> && SameType<Hash::result_type, size_t> && CopyConstructible<Hash> && CopyConstructible<Pred> && AllocatableElement<Alloc, Pred, const Pred&> && AllocatableElement<Alloc, Pred, Pred&&> && AllocatableElement<Alloc, Hash, const Hash&> && AllocatableElement<Alloc, Hash, Hash&&> class unordered_multimap { ... }; }23.5.3p3 Class template unordered_set [unord.set]
namespace std { template <ValueType Value, Callable<auto, const Value&> Hash = hash<Value>,PredicateEquivalenceRelation<auto, Value, Value> class Pred = equal_to<Value>, Allocator Alloc = allocator<Value> > requires NothrowDestructible<Value> && SameType<Hash::result_type, size_t> && CopyConstructible<Hash> && CopyConstructible<Pred> && AllocatableElement<Alloc, Pred, const Pred&> && AllocatableElement<Alloc, Pred, Pred&&> && AllocatableElement<Alloc, Hash, const Hash&> && AllocatableElement<Alloc, Hash, Hash&&> class unordered_set { ... }; }23.5.4p3 Class template unordered_multiset [unord.multiset]
namespace std { template <ValueType Value, Callable<auto, const Value&> Hash = hash<Value>,PredicateEquivalenceRelation<auto, Value, Value> class Pred = equal_to<Value>, Allocator Alloc = allocator<Value> > requires NothrowDestructible<Value> && SameType<Hash::result_type, size_t> && CopyConstructible<Hash> && CopyConstructible<Pred> && AllocatableElement<Alloc, Pred, const Pred&> && AllocatableElement<Alloc, Pred, Pred&&> && AllocatableElement<Alloc, Hash, const Hash&> && AllocatableElement<Alloc, Hash, Hash&&> class unordered_multiset { ... }; }
Section: X [concept.transform] Status: NAD Concepts Submitter: Daniel Krügler Opened: 2009-05-28 Last modified: 2009-07-15
View all other issues in [concept.transform].
View all issues with NAD Concepts status.
Discussion:
A recent news group article points to several defects in the specification of reference-related concepts.
One problem of the concept RvalueOf as currently defined in X [concept.transform]:
concept RvalueOf<typename T> {
typename type = T&&;
requires ExplicitlyConvertible<T&,type> && Convertible<T&&,type>;
}
template<typename T> concept_map RvalueOf<T&> {
typedef T&& type;
}
is that if T is an lvalue-reference, the requirement Convertible<T&&,type> isn't satisfied for lvalue-references, because after reference-collapsing in the concept definition we have Convertible<T&,type> in this case, which isn't satisfied in the concept map template and also is not the right constraint either. I think that the reporter is right that SameType requirements should do the job and that we also should use the new RvalueReference concept to specify a best matching type requirement.
Proposed resolution:
In X [concept.transform] before p. 4 change as indicated:
auto concept RvalueOf<typename T> {
typenameRvalueReference type = T&&;
requires ExplicitlyConvertible<T&, type> && Convertible<T&&, type>SameType<T&, type&>;
}
Section: 24.4.1 [iterator.traits] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-05-28 Last modified: 2009-07-15
View all other issues in [iterator.traits].
View all issues with NAD Concepts status.
Discussion:
The deprecated support for iterator_traits and legacy (unconstrained) iterators features the (exposition only) concept:
concept IsReference<typename T> { } // exposition only
template<typename T> concept_map IsReference<T&> { }
Now this looks exactly like the LvalueReference concept recently added to clause 20, so I wonder if we should use that instead? Then I consider the lack of rvalue-reference support, which means that move_iterator would always flag as merely supporting the input_iterator_tag category. This suggests we retain the exposition concept, but add a second concept_map to support rvalue references.
I would suggest adding the extra concept_map is the right way forward, but still wonder if the two exposition-only concepts in this clause might be worth promoting to clause 20. That question might better be answered with a fuller investigation of type_trait/concept unification though.
Proposed resolution:
In Iterator traits 24.4.1 [iterator.traits] para 4 add:
concept IsReference<typename T> { } // exposition only
template<typename T> concept_map IsReference<T&> { }
template<typename T> concept_map IsReference<T&&> { }
Section: X [iterator.syn] Status: NAD Concepts Submitter: Alisdair Meredith Opened: 2009-05-28 Last modified: 2009-07-16
View all issues with NAD Concepts status.
Discussion:
The <iterator> header synopsis declares a partial specialization of iterator_traits to support pointers, X [iterator.syn]. The implication is that specialization will be described in D10, yet it did not follow the rest of the deprecated material into this clause.
However, this is not as bad as it first seems! There are partial specializations of iterator_traits for types that satisfy the various Iterator concepts, and there are concept_maps for pointers to explicitly support the RandomAccessIterator concept, so the required template will be present - just not in the manner advertised.
I can see two obvious solutions:
I recommend option (ii) in the wording below
Option (ii) could be extended to strike all the declarations of deprecated material from the synopsis, as it is effectively duplicating D.10 anyway. This is the approach taken for deprecated library components in the 98/03 standards. This is probably a matter best left to the Editor though.
Proposed resolution:
In X [iterator.syn] strike:
template<class T> struct iterator_traits<T*>;
Section: 30 [thread] Status: NAD Concepts Submitter: LWG Opened: 2009-06-15 Last modified: 2009-07-15
View all other issues in [thread].
View all issues with NAD Concepts status.
Discussion:
Addresses US 93, JP 79, UK 333, JP 81
The thread chapter is not concept enabled.
Proposed resolution:
Section: 26 [numerics] Status: NAD Concepts Submitter: LWG Opened: 2009-06-15 Last modified: 2009-07-15
View all other issues in [numerics].
View all issues with NAD Concepts status.
Discussion:
Addresses US 84
The numerics chapter is not concept enabled.
The portion of this comment dealing with random numbers was resolved by N2836, which was accepted in Summit.
Proposed resolution:
Section: 27 [input.output] Status: NAD Concepts Submitter: LWG Opened: 2009-06-15 Last modified: 2009-07-15
View all other issues in [input.output].
View all issues with NAD Concepts status.
Discussion:
Addresses US 85, JP 67, JP 68, JP 69, JP 72, UK 308
The input/output chapter is not concept enabled.
Proposed resolution:
Section: 28 [re] Status: NAD Concepts Submitter: LWG Opened: 2009-06-15 Last modified: 2009-07-15
View all other issues in [re].
View all issues with NAD Concepts status.
Discussion:
Addresses US 86, UK 309, UK 310
The regular expressions chapter is not concept enabled.
Proposed resolution:
Section: 29 [atomics] Status: NAD Concepts Submitter: LWG Opened: 2009-06-15 Last modified: 2009-07-15
View other active issues in [atomics].
View all other issues in [atomics].
View all issues with NAD Concepts status.
Discussion:
Addresses US 87, UK 311
The atomics chapter is not concept enabled.
Needs to also consider issues 923 and 924.
Proposed resolution:
Section: 26.5.2.2 [rand.concept.urng] Status: NAD Concepts Submitter: Walter Brown Opened: 2009-06-25 Last modified: 2009-07-15
View all issues with NAD Concepts status.
Discussion:
In 26.5.2.2 [rand.concept.urng], we have the following:
concept UniformRandomNumberGenerator<typename G> : Callable<G> {
...
axiom NonemptyRange(G& g) {
G::min() < G::max();
}
...
}
Since the parameter G is in scope throughout the concept, there is no need for the axiom to be further parameterized, and so the axiom can be slightly simplified as:
axiom NonemptyRange() {
G::min() < G::max();
}
We can further reformulate so as to avoid any axiom machinery as:
requires True< G::min() < G::max() >;
This is not only a simpler statement of the same requirement, but also forces the requirement to be checked.
Proposed resolution:
In 26.5.2.2 [rand.concept.urng], replace the NonemptyRange axiom by:
axiom NonemptyRange(G& g) { G::min() < G::max(); }requires True< G::min() < G::max() >;
Section: 30.6.4 [futures.promise] Status: NAD Submitter: LWG Opened: 2009-06-28 Last modified: 2009-07-17
View other active issues in [futures.promise].
View all other issues in [futures.promise].
View all issues with NAD status.
Discussion:
Addresses UK 341
Description
promise::swap accepts its parameter by lvalue reference. This is inconsistent with other types that provide a swap member function, where those swap functions accept an rvalue reference
Suggestion
Change promise::swap to take an rvalue reference.
Notes
Create an issue. Detlef will look into it. Probably ready as it.
[ 2009-07 Frankfurt ]
NAD, by virtue of the changed rvalue rules and swap signatures from Summit.
Proposed resolution:
Section: 20.3.3 [pairs] Status: NAD Concepts Submitter: Dave Abrahams Opened: 2009-07-01 Last modified: 2009-07-16
View other active issues in [pairs].
View all other issues in [pairs].
View all issues with NAD Concepts status.
Discussion:
LessThanComparable requires (and provides default implementations for) <=,>, and >=. However, the defaults don't take effect in unconstrained code.
Still, it's a problem to have types acting one way in constrained code and another in unconstrained code, except in cases of syntax adaptation. It's also inconsistent with the containers, which supply all those operators.
Totally Unbiased Suggested Resolution:
accept the exported concept maps proposal and change the way this stuff is handled to use an explicit exported concept map rather than nested function templates
e.g., remove from the body of std::list
template <LessThanComparable T, class Allocator> bool operator< (const list<T,Allocator>& x, const list<T,Allocator>& y); template <LessThanComparable T, class Allocator> bool operator> (const list<T,Allocator>& x, const list<T,Allocator>& y); template <LessThanComparable T, class Allocator> bool operator>=(const list<T,Allocator>& x, const list<T,Allocator>& y); template <LessThanComparable T, class Allocator> bool operator<=(const list<T,Allocator>& x, const list<T,Allocator>& y);
and add this concept_map afterwards:
template <LessThanComparable T, class Allocator>
export concept_map LessThanComparable<list<T,Allocator> >
{
bool operator<(const list<T,Allocator>& x, const list<T,Allocator>& y);
}
do similarly for std::pair. While you're at it, do the same for operator== and != everywhere, and seek out other such opportunities.
Alternative Resolution: keep the ugly, complex specification and add the missing operators to std::pair.
Proposed resolution:
Section: 20.3.7.2 [bitset.members] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2009-07-02 Last modified: 2009-07-27
View all other issues in [bitset.members].
View all issues with NAD Editorial status.
Discussion:
The following wording seems a little unusual to me:
p42/43 20.3.7.2 [bitset.members]
bool operator==(const bitset<N>& rhs) const;-42- Returns: A nonzero value if the value of each bit in *this equals the value of the corresponding bit in rhs.bool operator!=(const bitset<N>& rhs) const;-43- Returns: A nonzero value if !(*this == rhs).
"A nonzero value" may be well defined as equivalent to the literal 'true' for Booleans, but the wording is clumsy. I suggest replacing "A nonzero value" with the literal 'true' (in appropriate font) in each case.
[ 2009-07-24 Alisdair recommends NAD Editorial. ]
[ 2009-07-27 Pete adds: ]
It's obviously editorial. There's no need for further discussion.
[ 2009-07-27 Howard sets to NAD Editorial. ]
Proposed resolution:
Change 20.3.7.2 [bitset.members] p42-43:
bool operator==(const bitset<N>& rhs) const;-42- Returns:A nonzero valuetrue if the value of each bit in *this equals the value of the corresponding bit in rhs.bool operator!=(const bitset<N>& rhs) const;-43- Returns:A nonzero valuetrue if !(*this == rhs).