Document Number: | |
---|---|
Date: | |
Revises: | |
Editor: | Google DeepMind |
Note: this is an early draft. It’s known to be incomplet and incorrekt, and it has lots of bad formatting.
In this document, the phrase
Clauses and subclauses in this document are annotated with a so-called stable name, presented in square brackets next to the (sub)clause heading (such as "[introduction]" for this clause). Stable names aid in the discussion and evolution of this document by serving as stable references to subclauses across editions that are unaffected by changes of subclause numbering.
This document describes extensions to the C++
Standard Library (
Some of the library components in this document might be considered for standardization in a future version of C++, but they are not currently part of any C++ standard. Some of the components in this document might never be standardized, and others might be standardized in a substantially changed form.
The goal of this document is to build more widespread existing practice for an expanded C++ standard library. It gives advice on extensions to those vendors who wish to provide them.
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
For the purposes of this document, the terms and definitions given in ISO/IEC 14882:2020 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
Since the extensions described in this document
are experimental and not part of the C++ standard library, they
should not be declared directly within namespace
std
.
Unless otherwise specified, all components described in this document either:
::experimental::fundamentals_v3
to a namespace defined in the C++ Standard Library,
such as std
or std::chrono
, or
std
.
std::experimental::fundamentals_v3::pmr
because the C++ Standard Library defines std::pmr
.
— end example ]
Each header described in this document shall import the contents of
std::experimental::fundamentals_v3
into
std::experimental
as if by
namespace std::experimental::inline fundamentals_v3 {}
This document also describes some experimental modifications to existing interfaces in the C++ Standard Library.
Unless otherwise specified, references to other entities
described in this document are assumed to be
qualified with std::experimental::fundamentals_v3::
,
and references to entities described in the standard are assumed
to be qualified with std::
.
Extensions that are expected to eventually be added to an
existing header <meow>
are provided inside the
<experimental/meow>
header, which shall include
the standard contents of <meow>
as if by
#include <meow>
New headers are also provided in the
<experimental/>
directory, but without such an
#include
.
|
|
|
std::experimental::fundamentals_v4
,
std::experimental::fundamentals_v5
, etc., with the
most recent implemented version inlined into
std::experimental
.
— end note ]
For the sake of improved portability between partial implementations of various C++ standards,
implementers and programmers are recommended to follow the guidelines in this section concerning feature-test macros.
Implementers who provide a new standard feature should define a macro with the recommended name,
in the same circumstances under which the feature is available (for example, taking into account relevant command-line options),
to indicate the presence of support for that feature.
Implementers should define that macro with the value specified in
the most recent version of this document that they have implemented.
The recommended macro name is "__cpp_lib_experimental_
" followed by the string in the "Macro Name Suffix" column.
Programmers who wish to determine whether a feature is available in an implementation should base that determination on
the presence of the header (determined with __has_include(<header/name>)
) and
the state of the macro with the recommended name.
(The absence of a tested feature may result in a program with decreased functionality, or the relevant functionality may be provided in a different way.
A program that strictly depends on support for a feature can just try to use the feature unconditionally;
presumably, on an implementation lacking necessary support, translation will fail.)
Feature | Primary Section | Macro Name Suffix | Value | Header |
---|---|---|---|---|
Const-propagating wrapper | propagate_const
| 201505 | <experimental/propagate_const>
| |
Generic scope guard and RAII wrapper | scope
| 201902 | <experimental/scope>
| |
Invocation type traits | invocation_type |
201406 | <experimental/type_traits> |
|
Detection metaprograms | detect |
201505 | <experimental/type_traits> |
|
Polymorphic allocator for std::function |
function_polymorphic_allocator |
202211 | <experimental/functional> |
|
Polymorphic memory resources | memory_resources |
201803 | <experimental/memory_resouce> |
|
Non-owning pointer wrapper | observer_ptr
| 201411 | <experimental/memory>
| |
Delimited iterators | ostream_joiner |
201411 | <experimental/iterator> |
|
Random sampling | sample |
201402 | <experimental/algorithm> |
|
Replacement for std::rand |
randint |
201511 | <experimental/random> |
Implementations that conform to this document shall behave as if the modifications contained in this section are made to ISO/IEC 14882:2020.
References to clauses within ISO/IEC 14882:2020 are written as "C++20 §3.2".
Unless otherwise specified, the whole of
the Library introduction of ISO/IEC 14882:2020 (
The following modifications to the Library introduction (scope_success
(
The requirements of
The requirements of
<experimental/propagate_const>
synopsisnamespace std {
namespace experimental::inline fundamentals_v3 {
// 6.1.2.1, Overview
template <class T> class propagate_const;
// 6.1.2.9, Relational operators
template <class T>
constexpr bool operator==(const propagate_const<T>& pt, nullptr_t);
template <class T>
constexpr bool operator==(nullptr_t, const propagate_const<T>& pu);
template <class T>
constexpr bool operator!=(const propagate_const<T>& pt, nullptr_t);
template <class T>
constexpr bool operator!=(nullptr_t, const propagate_const<T>& pu);
template <class T, class U>
constexpr bool operator==(const propagate_const<T>& pt,
const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator!=(const propagate_const<T>& pt,
const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator<(const propagate_const<T>& pt,
const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator>(const propagate_const<T>& pt,
const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator<=(const propagate_const<T>& pt,
const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator>=(const propagate_const<T>& pt,
const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator==(const propagate_const<T>& pt, const U& u);
template <class T, class U>
constexpr bool operator!=(const propagate_const<T>& pt, const U& u);
template <class T, class U>
constexpr bool operator<(const propagate_const<T>& pt, const U& u);
template <class T, class U>
constexpr bool operator>(const propagate_const<T>& pt, const U& u);
template <class T, class U>
constexpr bool operator<=(const propagate_const<T>& pt, const U& u);
template <class T, class U>
constexpr bool operator>=(const propagate_const<T>& pt, const U& u);
template <class T, class U>
constexpr bool operator==(const T& t, const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator!=(const T& t, const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator<(const T& t, const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator>(const T& t, const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator<=(const T& t, const propagate_const<U>& pu);
template <class T, class U>
constexpr bool operator>=(const T& t, const propagate_const<U>& pu);
// 6.1.2.10, Specialized algorithms
template <class T>
constexpr void swap(propagate_const<T>& pt,
propagate_const<T>& pt2) noexcept(see below);
// 6.1.2.11, Underlying pointer access
template <class T>
constexpr const T& get_underlying(const propagate_const<T>& pt) noexcept;
template <class T>
constexpr T& get_underlying(propagate_const<T>& pt) noexcept;
} // namespace experimental::inline fundamentals_v3
// 6.1.2.12, Hash support
template <class T> struct hash;
template <class T>
struct hash<experimental::fundamentals_v3::propagate_const<T>>;
// 6.1.2.13, Comparison function objects
template <class T> struct equal_to;
template <class T>
struct equal_to<experimental::fundamentals_v3::propagate_const<T>>;
template <class T> struct not_equal_to;
template <class T>
struct not_equal_to<experimental::fundamentals_v3::propagate_const<T>>;
template <class T> struct less;
template <class T>
struct less<experimental::fundamentals_v3::propagate_const<T>>;
template <class T> struct greater;
template <class T>
struct greater<experimental::fundamentals_v3::propagate_const<T>>;
template <class T> struct less_equal;
template <class T>
struct less_equal<experimental::fundamentals_v3::propagate_const<T>>;
template <class T> struct greater_equal;
template <class T>
struct greater_equal<experimental::fundamentals_v3::propagate_const<T>>;
} // namespace std
propagate_const
namespace std::experimental::inline fundamentals_v3 {
template <class T> class propagate_const {
public:
using element_type = remove_reference_t<decltype(*declval<T&>())>;
// 6.1.2.4, Constructors
constexpr propagate_const() = default;
propagate_const(const propagate_const& p) = delete;
constexpr propagate_const(propagate_const&& p) = default;
template <class U>
explicit(!is_convertible_v<U, T>)
constexpr propagate_const(propagate_const<U>&& pu);
template <class U>
explicit(!is_convertible_v<U, T>)
constexpr propagate_const(U&& u);
// 6.1.2.5, Assignment
propagate_const& operator=(const propagate_const& p) = delete;
constexpr propagate_const& operator=(propagate_const&& p) = default;
template <class U>
constexpr propagate_const& operator=(propagate_const<U>&& pu);
template <class U>
constexpr propagate_const& operator=(U&& u);
// 6.1.2.6, Const observers
explicit constexpr operator bool() const;
constexpr const element_type* operator->() const;
constexpr operator const element_type*() const; // Not always defined
constexpr const element_type& operator*() const;
constexpr const element_type* get() const;
// 6.1.2.7, Non-const observers
constexpr element_type* operator->();
constexpr operator element_type*(); // Not always defined
constexpr element_type& operator*();
constexpr element_type* get();
// 6.1.2.8, Modifiers
constexpr void swap(propagate_const& pt) noexcept(is_nothrow_swappable<T>);
private:
T t_; //exposition only
};
} // namespace std::experimental::inline fundamentals_v3
propagate_const
is a wrapper around a pointer-like object type T
which treats the wrapped pointer as a pointer to const
when
the wrapper is accessed through a const
access path.
T
T
shall be a cv-unqualified pointer-to-object type or a cv-unqualified class type for which
decltype(*declval<T&>())
is an lvalue reference to object type; otherwise
the program is ill-formed.
propagate_const<const int*>
is well-formed but propagate_const<int* const> is not
.
— end note ]
T
If T
is class
type then it shall satisfy the following requirements. In this subclause
t
denotes an lvalue of type T
, ct
denotes as_const(t)
.
T
and const T
shall be contextually convertible to bool
.
If T
is implicitly convertible to element_type*
,
(element_type*)t == t.get()
shall be true
.
If const T
is implicitly convertible to const element_type*
,
(const element_type*)ct == ct.get()
shall be true
.
Expression | Return type | Pre-conditions | Operational semantics |
---|---|---|---|
t.get() |
element_type* |
||
ct.get() |
const element_type* or element_type* |
|
t.get() == ct.get() . |
*t |
element_type& |
t.get() != nullptr |
*t refers to the same object as *(t.get()) |
*ct |
const element_type& or element_type& |
ct.get() != nullptr |
*ct refers to the same object as *(ct.get()) |
t.operator->() |
element_type* |
t.get() != nullptr |
t.operator->() == t.get() |
ct.operator->() |
const element_type* or element_type* |
ct.get() != nullptr |
ct.operator->() == ct.get() |
(bool)t |
bool |
|
(bool)t is equivalent to t.get() != nullptr |
(bool)ct |
bool |
|
(bool)ct is equivalent to ct.get() != nullptr |
template <class U>
explicit(!is_convertible_v<U, T>)
constexpr propagate_const(propagate_const<U>&& pu);
is_constructible_v<T, U>
is true.
t_
as if
direct-non-list-initializing an object of type T
with the
expression std::move(pu.t_)
.
template <class U>
explicit(!is_convertible_v<U, T>) constexpr propagate_const(U&& u);
is_constructible_v<T, U>
is true
and decay_t<U>
is not a specialization of propagate_const
.
t_
as if
direct-non-list-initializing an object of type T
with
the expression std::forward<U>(u)
.
template <class U>
constexpr propagate_const& operator=(propagate_const<U>&& pu);
U
is implicitly convertible to T
.
t_ = std::move(pu.t_)
.*this
.template <class U>
constexpr propagate_const& operator=(U&& u);
U
is implicitly convertible to T
and
decay_t<U>
is not a specialization of propagate_const
.
t_ = std::forward<U>(u)
.*this
.explicit constexpr operator bool() const;
(bool)t_
.constexpr const element_type* operator->() const;
get() != nullptr
.get()
.constexpr operator const element_type*() const;
T
is an object pointer type or
has an implicit conversion to const element_type*
.
get()
.constexpr const element_type& operator*() const;
get() != nullptr
.*get()
.constexpr const element_type* get() const;
t_
if T
is an object pointer type,
otherwise t_.get()
.
constexpr element_type* operator->();
get() != nullptr
.get()
.constexpr operator element_type*();
T
is an object pointer type or
has an implicit conversion to element_type*
.
get()
.constexpr element_type& operator*();
get() != nullptr
.*get()
.constexpr element_type* get();
t_
if T
is an object pointer type,
otherwise t_.get()
.
constexpr void swap(propagate_const& pt) noexcept(is_nothrow_swappable<T>);
T
are swappable
(swap(t_, pt.t_)
.template <class T>
constexpr bool operator==(const propagate_const<T>& pt, nullptr_t);
pt.t_ == nullptr
.template <class T>
constexpr bool operator==(nullptr_t, const propagate_const<T>& pt);
nullptr == pt.t_
.template <class T>
constexpr bool operator!=(const propagate_const<T>& pt, nullptr_t);
pt.t_ != nullptr
.template <class T>
constexpr bool operator!=(nullptr_t, const propagate_const<T>& pt);
nullptr != pt.t_
.template <class T, class U>
constexpr bool operator==(const propagate_const<T>& pt,
const propagate_const<U>& pu);
pt.t_ == pu.t_
.template <class T, class U>
constexpr bool operator!=(const propagate_const<T>& pt,
const propagate_const<U>& pu);
pt.t_ != pu.t_
.template <class T, class U>
constexpr bool operator<(const propagate_const<T>& pt,
const propagate_const<U>& pu);
pt.t_ < pu.t_
.template <class T, class U>
constexpr bool operator>(const propagate_const<T>& pt,
const propagate_const<U>& pu);
pt.t_ > pu.t_
.template <class T, class U>
constexpr bool operator<=(const propagate_const<T>& pt,
const propagate_const<U>& pu);
pt.t_ <= pu.t_
.template <class T, class U>
constexpr bool operator>=(const propagate_const<T>& pt,
const propagate_const<U>& pu);
pt.t_ >= pu.t_
.template <class T, class U>
constexpr bool operator==(const propagate_const<T>& pt, const U& u);
pt.t_ == u
.template <class T, class U>
constexpr bool operator!=(const propagate_const<T>& pt, const U& u);
pt.t_ != u
.template <class T, class U>
constexpr bool operator<(const propagate_const<T>& pt, const U& u);
pt.t_ < u
.template <class T, class U>
constexpr bool operator>(const propagate_const<T>& pt, const U& u);
pt.t_ > u
.template <class T, class U>
constexpr bool operator<=(const propagate_const<T>& pt, const U& u);
pt.t_ <= u
.template <class T, class U>
constexpr bool operator>=(const propagate_const<T>& pt, const U& u);
pt.t_ >= u
.template <class T, class U>
constexpr bool operator==(const T& t, const propagate_const<U>& pu);
t == pu.t_
.template <class T, class U>
constexpr bool operator!=(const T& t, const propagate_const<U>& pu);
t != pu.t_
.template <class T, class U>
constexpr bool operator<(const T& t, const propagate_const<U>& pu);
t < pu.t_
.template <class T, class U>
constexpr bool operator>(const T& t, const propagate_const<U>& pu);
t > pu.t_
.template <class T, class U>
constexpr bool operator<=(const T& t, const propagate_const<U>& pu);
t <= pu.t_
.template <class T, class U>
constexpr bool operator>=(const T& t, const propagate_const<U>& pu);
t >= pu.t_
.template <class T>
constexpr void swap(propagate_const<T>& pt1,
propagate_const<T>& pt2) noexcept(see below);
is_swappable_v<T>
is true
.pt1.swap(pt2)
.noexcept
is equivalent to:
noexcept(pt1.swap(pt2))
Access to the underlying object pointer type is through free functions rather than member functions. These functions are intended to resemble cast operations to encourage caution when using them.
template <class T>
constexpr const T& get_underlying(const propagate_const<T>& pt) noexcept;
template <class T>
constexpr T& get_underlying(propagate_const<T>& pt) noexcept;
template <class T>
struct hash<experimental::fundamentals_v3::propagate_const<T>>;
The specialization hash<experimental::fundamentals_v3::propagate_const<T>>
is enabled (hash<T>
is enabled.
When enabled, for an object p
of type propagate_const<T>
,
hash<experimental::fundamentals_v3::propagate_const<T>>()(p)
evaluates to the same value as hash<T>()(p.t_)
.
template <class T>
struct equal_to<experimental::fundamentals_v3::propagate_const<T>>;
For objects p, q
of type propagate_const<T>
,
equal_to<experimental::fundamentals_v3::propagate_const<T>>()(p,
q)
shall evaluate to the same value as equal_to<T>()(p.t_,
q.t_)
.
equal_to<T>
is well-formed.
equal_to<T>
is well-defined.
template <class T>
struct not_equal_to<experimental::fundamentals_v3::propagate_const<T>>;
For objects p, q
of type propagate_const<T>
,
not_equal_to<experimental::fundamentals_v3::propagate_const<T>>()(p, q)
shall evaluate to the same value as not_equal_to<T>()(p.t_, q.t_)
.
not_equal_to<T>
is well-formed.
not_equal_to<T>
is well-defined.
template <class T>
struct less<experimental::fundamentals_v3::propagate_const<T>>;
For objects p, q
of type propagate_const<T>
,
less<experimental::fundamentals_v3::propagate_const<T>>()(p, q)
shall evaluate to the same value as less<T>()(p.t_, q.t_)
.
less<T>
is well-formed.
less<T>
is well-defined.
template <class T>
struct greater<experimental::fundamentals_v3::propagate_const<T>>;
For objects p, q
of type propagate_const<T>
,
greater<experimental::fundamentals_v3::propagate_const<T>>()(p, q)
shall evaluate to the same value as greater<T>()(p.t_, q.t_)
.
greater<T>
is well-formed.
greater<T>
is well-defined.
template <class T>
struct less_equal<experimental::fundamentals_v3::propagate_const<T>>;
For objects p, q
of type propagate_const<T>
,
less_equal<experimental::fundamentals_v3::propagate_const<T>>()(p, q)
shall evaluate to the same value as less_equal<T>()(p.t_, q.t_)
.
less_equal<T>
is well-formed.
less_equal<T>
is well-defined.
template <class T>
struct greater_equal<experimental::fundamentals_v3::propagate_const<T>>;
For objects p, q
of type propagate_const<T>
,
greater_equal<experimental::fundamentals_v3::propagate_const<T>>()(p, q)
shall evaluate to the same value as greater_equal<T>()(p.t_, q.t_)
.
greater_equal<T>
is well-formed.
greater_equal<T>
is well-defined.
<experimental/scope>
synopsisnamespace std::experimental::inline fundamentals_v3 {
// 6.2.2, Class templates scope_exit, scope_fail, and scope_success
template <class EF>
class scope_exit;
template <class EF>
class scope_fail;
template <class EF>
class scope_success;
// 6.2.3, Class template unique_resource
template <class R, class D>
class unique_resource;
// 6.2.3.6, unique_resource creation
template <class R, class D, class S=decay_t<R>>
unique_resource<decay_t<R>, decay_t<D>>
make_unique_resource_checked(
R&& r, const S& invalid, D&& d) noexcept(see below);
} // namespace std::experimental::inline fundamentals_v3
scope_exit
, scope_fail
, and scope_success
The class templates scope_exit
, scope_fail
,
and scope_success
define scope guards that wrap a
function object to be called on their destruction.
In this subclause, the placeholder scope-guard
denotes each of these class templates. In descriptions of the
class members, scope-guard
refers to the enclosing
class.
namespace std::experimental::inline fundamentals_v3 {
template <class EF> class scope-guard {
public:
template <class EFP>
explicit scope-guard(EFP&& f) noexcept(see below);
scope-guard(scope-guard&& rhs) noexcept(see below);
scope-guard(const scope-guard&) = delete;
scope-guard& operator=(const scope-guard&) = delete;
scope-guard& operator=(scope-guard&&) = delete;
~scope-guard () noexcept(see below);
void release() noexcept;
private:
EF exit_function; // exposition only
bool execute_on_destruction{true}; // exposition only
int uncaught_on_creation{uncaught_exceptions()}; // exposition only
};
template <class EF>
scope-guard(EF) -> scope-guard<EF>;
} // namespace std::experimental::inline fundamentals_v3
The class template scope_exit
is a general-purpose
scope guard that calls its exit function when a scope is exited. The
class templates scope_fail
and scope_success
share the scope_exit
interface, only the situation when the
exit function is called differs.
void grow(vector<int>& v) {
scope_success guard([]{ cout << "Good!" << endl; });
v.resize(1024);
}
— end example ]
scope_success
or scope_exit
object refers to a local variable
of the function where it is defined, e.g., as a lambda capturing
the variable by reference, and that variable is used as a return
operand in that function, it is possible for that variable to already have been
returned when the scope-guard
’s destructor
executes, calling the exit function. This can lead to surprising
behavior.
— end note ]
Template argument EF
shall be a function object type
(EF
is an object type, it shall meet the g
of type
remove_reference_t<EF>
, the expression
g()
shall be well-formed.
The constructor parameter f
in the following constructors
shall be a reference to a function or a reference to a function
object (
template <class EFP>
explicit scope-guard(EFP&& f) noexcept(
is_nothrow_constructible_v<EF, EFP> ||
is_nothrow_constructible_v<EF, EFP&>);
is_same_v<remove_cvref_t<EFP>,
scope-guard>
is false
and
is_constructible_v<EF, EFP>
is true
.
f()
is well-formed.
f()
has well-defined behavior.
For scope_exit
and scope_fail
,
calling f()
does not throw an exception.
EFP
is not an lvalue reference type and
is_nothrow_constructible_v<EF, EFP>
is true
, initialize exit_function
with std::forward<EFP>(f)
;
otherwise initialize exit_function
with f
.
For scope_exit
and scope_fail
,
if the initialization of exit_function
throws an exception,
calls f()
.
scope_success
, f()
will not be
called if the initialization fails.
— end note ]
exit_function
.
scope-guard(scope-guard&& rhs) noexcept(see below)
(is_nothrow_move_constructible_v<EF> || is_copy_constructible_v<EF>)
is true
.
EF
is an object type:
is_nothrow_move_constructible_v<EF>
is true
,
EF
meets the EF
meets the is_nothrow_move_constructible_v<EF>
is true
,
initializes exit_function
with std::forward<EF>(rhs.exit_function)
,
otherwise initializes exit_function
with rhs.exit_function
.
Initializes execute_on_destruction
from rhs.execute_on_destruction
and
uncaught_on_creation
from rhs.uncaught_on_creation
.
If construction succeeds, call rhs.release()
.
execute_on_destruction
yields the value rhs.execute_on_destruction
yielded before the construction. uncaught_on_creation
yields the value
rhs.uncaught_on_creation
yielded before the construction.
exit_function
.
noexcept
is equivalent to:
is_nothrow_move_constructible_v<EF> || is_nothrow_copy_constructible_v<EF>
~scope_exit() noexcept(true);
if (execute_on_destruction)
exit_function();
~scope_fail() noexcept(true);
if (execute_on_destruction && uncaught_exceptions() > uncaught_on_creation)
exit_function();
~scope_success() noexcept(noexcept(exit_function()));
if (execute_on_destruction && uncaught_exceptions() <= uncaught_on_creation)
exit_function();
noexcept(exit_function())
is false
,
exit_function()
may throw an exception,
notwithstanding the restrictions of exit_function()
.
void release() noexcept;
execute_on_destruction = false
.
unique_resource
namespace std::experimental::inline fundamentals_v3 {
template <class R, class D> class unique_resource {
public:
// 6.2.3.2, Constructors
unique_resource();
template <class RR, class DD>
unique_resource(RR&& r, DD&& d) noexcept(see below);
unique_resource(unique_resource&& rhs) noexcept(see below);
// 6.2.3.3, Destructor
~unique_resource();
// 6.2.3.4, Assignment
unique_resource& operator=(unique_resource&& rhs) noexcept(see below);
// 6.2.3.5, Other member functions
void reset() noexcept;
template <class RR>
void reset(RR&& r);
void release() noexcept;
const R& get() const noexcept;
see below operator*() const noexcept;
R operator->() const noexcept;
const D& get_deleter() const noexcept;
private:
using R1 = conditional_t<is_reference_v<
R>, reference_wrapper<remove_reference_t<R>>, R>; // exposition only
R1 resource; // exposition only
D deleter; // exposition only
bool execute_on_reset{true}; // exposition only
};
template<class R, class D>
unique_resource(R, D) -> unique_resource<R, D>;
} // namespace std::experimental::inline fundamentals_v3
unique_resource
is a universal RAII wrapper for resource handles.
Typically, such resource handles are of trivial type and come with a factory function
and a clean-up or deleter function that do not throw exceptions. The clean-up function
together with the result of the creation function is used to create a unique_resource
variable, that on destruction will call the clean-up function. Access to the underlying
resource handle is achieved through get()
and in case of a pointer type
resource through a set of convenience pointer operator functions.
— end note ]
The template argument D
shall meet the requirements of a
d
of type D
and a lvalue r
of
type R
, the expression d(r)
shall be well-formed.
D
shall either meet the D
shall meet the is_nothrow_move_constructible_v<D>
shall be true
.
For the purpose of this subclause, a resource type T
is an object type that meets the requirements of is_nothrow_move_constructible_v<T>
is true
,
or is an lvalue reference to a resource type. R
shall be a resource type.
For the scope of the adjacent subclauses,
let RESOURCE
be defined as follows:
resource.get()
if is_reference_v<R>
is true
,resource
otherwise.unique_resource()
is_default_constructible_v<R> &&
is_default_constructible_v<D>
is true
.
resource
and deleter
;
execute_on_reset
is initialized with false
.
template <class RR, class DD>
unique_resource(RR&& r, DD&& d) noexcept(see below)
is_constructible_v<R1, RR> &&
is_constructible_v<D , DD> &&
(is_nothrow_constructible_v<R1, RR> || is_constructible_v<R1,RR&>) &&
(is_nothrow_constructible_v<D , DD> || is_constructible_v<D ,DD&>)
is true
.
R1
or D
is a specialization of reference_wrapper
.
— end note ]
d(r)
, d(RESOURCE)
and deleter(RESOURCE)
are well-formed.
d(r)
, d(RESOURCE)
or deleter(RESOURCE)
has well-defined behavior and
does not throw an exception.
is_nothrow_constructible_v<R1, RR>
is true
,
initializes resource
with std::forward<RR>(r)
,
otherwise initializes resource
with r
.
Then, if is_nothrow_constructible_v<D, DD>
is true,
initializes deleter
with std::forward<DD>(d)
,
otherwise initializes deleter
with d
.
If initialization of resource
throws an exception,
calls d(r)
.
If initialization of deleter
throws an exception, calls d(RESOURCE)
.
resource
or deleter
.
noexcept
is equivalent to:
(is_nothrow_constructible_v<R1, RR> || is_nothrow_constructible_v<R1, RR&>) &&
(is_nothrow_constructible_v<D , DD> || is_nothrow_constructible_v<D , DD&>)
unique_resource(unique_resource&& rhs) noexcept(see below);
resource
as follows:
is_nothrow_move_constructible_v<R1>
is
true
, from std::move(rhs.resource)
;rhs.resource
.resource
throws an exception,
rhs
is left owning the resource and will free it in due time.
— end note ]
deleter
as follows:
is_nothrow_move_constructible_v<D>
is
true
, from std::move(rhs.deleter)
;rhs.deleter
.deleter
throws an exception and
is_nothrow_move_constructible_v<R1>
is true
and rhs.execute_on_reset
is true:
rhs.deleter(RESOURCE);
rhs.release();
Finally, execute_on_reset
is initialized with
exchange(rhs.execute_on_reset, false)
.
noexcept
is equivalent to:
is_nothrow_move_constructible_v<R1> && is_nothrow_move_constructible_v<D>
~unique_resource();
reset()
.unique_resource& operator=(unique_resource&& rhs) noexcept(see below);
is_nothrow_move_assignable_v<R1>
is true
,
R1
meets the R1
meets the is_nothrow_move_assignable_v<D>
is true
,
D
meets the D
meets the reset();
if constexpr (is_nothrow_move_assignable_v<R1>) {
if constexpr (is_nothrow_move_assignable_v<D>) {
resource = std::move(rhs.resource);
deleter = std::move(rhs.deleter);
} else {
deleter = rhs.deleter;
resource = std::move(rhs.resource);
}
} else {
if constexpr (is_nothrow_move_assignable_v<D>) {
resource = rhs.resource;
deleter = std::move(rhs.deleter);
} else {
resource = rhs.resource;
deleter = rhs.deleter;
}
}
execute_on_reset = exchange(rhs.execute_on_reset, false);
rhs
intact and *this
in the released state.
— end note ]
*this
.noexcept
is equivalent to:
is_nothrow_move_assignable_v<R1> && is_nothrow_move_assignable_v<D>
void reset() noexcept;
if (execute_on_reset) {
execute_on_reset = false;
deleter(RESOURCE);
}
template <class RR> void reset(RR&& r);
resource
is well-formed.
deleter(r)
is well-formed.
deleter(r)
has well-defined behavior
and does not throw an exception.
reset();
if constexpr (is_nothrow_assignable_v<R1&, RR>) {
resource = std::forward<RR>(r);
} else {
resource = as_const(r);
}
execute_on_reset = true;
If copy-assignment of resource
throws an exception,
calls deleter(r)
.
void release() noexcept;
execute_on_reset = false
.const R& get() const noexcept;
resource
.see below operator*() const noexcept;
is_pointer_v<R>
is true
and
is_void_v<remove_pointer_t<R>>
is false
.
return *get();
add_lvalue_reference_t<remove_pointer_t<R>>
.
R operator->() const noexcept;
is_pointer_v<R>
is true
.
get()
.const D& get_deleter() const noexcept;
deleter
.unique_resource
creationtemplate <class R, class D, class S=decay_t<R>>
unique_resource<decay_t<R>, decay_t<D>>
make_unique_resource_checked(R&& resource, const S& invalid, D&& d)
noexcept(is_nothrow_constructible_v<decay_t<R>, R> &&
is_nothrow_constructible_v<decay_t<D>, D>);
(resource == invalid ? true : false)
is well-formed.
(resource == invalid ? true : false)
has well-defined behavior and does not throw an exception.
std::forward<R>(resource), std::forward<D>(d)
,
and !bool(resource == invalid)
.
Any failure during construction of the return value will not call d(resource)
if bool(resource == invalid)
is true
.
fclose
when fopen
fails.
auto file = make_unique_resource_checked(
::fopen("potentially_nonexistent_file.txt", "r"),
nullptr,
[](auto fptr){ ::fclose(fptr); });
— end example ]
#include <type_traits>
namespace std::experimental::inline fundamentals_v3 {
// 6.3.2, Other type transformations
template <class> class invocation_type; // not defined
template <class F, class... ArgTypes> class invocation_type<F(ArgTypes...)>;
template <class> class raw_invocation_type; // not defined
template <class F, class... ArgTypes> class raw_invocation_type<F(ArgTypes...)>;
template <class T>
using invocation_type_t = typename invocation_type<T>::type;
template <class T>
using raw_invocation_type_t = typename raw_invocation_type<T>::type;
// 6.3.3, Detection idiom
struct nonesuch;
template <template<class...> class Op, class... Args>
using is_detected = see below;
template <template<class...> class Op, class... Args>
inline constexpr bool is_detected_v
= is_detected<Op, Args...>::value;
template <template<class...> class Op, class... Args>
using detected_t = see below;
template <class Default, template<class...> class Op, class... Args>
using detected_or = see below;
template <class Default, template<class...> class Op, class... Args>
using detected_or_t = typename detected_or<Default, Op, Args...>::type;
template <class Expected, template<class...> class Op, class... Args>
using is_detected_exact = is_same<Expected, detected_t<Op, Args...>>;
template <class Expected, template<class...> class Op, class... Args>
inline constexpr bool is_detected_exact_v
= is_detected_exact<Expected, Op, Args...>::value;
template <class To, template<class...> class Op, class... Args>
using is_detected_convertible = is_convertible<detected_t<Op, Args...>, To>;
template <class To, template<class...> class Op, class... Args>
inline constexpr bool is_detected_convertible_v
= is_detected_convertible<To, Op, Args...>::value;
} // namespace std::experimental::inline fundamentals_v3
This subclause contains templates that may be used to transform one type to another following some predefined rule.
Each of the templates in this subclause shall be a
Within this section, define the invocation parameters of INVOKE(f, t1, t2, ..., tN)
as follows,
in which T1
is the possibly cv-qualified type of t1
and U1
denotes T1&
if t1
is an lvalue
or T1&&
if t1
is an rvalue:
f
is a pointer to a member function of a class T
the U1
followed by
the parameters of f
matched by t2
, ..., tN
.
N == 1
and f
is a pointer to member data of a class T
the U1
.
f
is a class object,
the t1
, ..., tN
of the best viable function (t1
, ..., tN
among the function call operators and surrogate call functions of f
.
f
matching t1
, ... tN
.
In all of the above cases,
if an argument tI
matches the ellipsis in the function's tI
.
S
is defined as
struct S {
int f(double const &) const;
void operator()(int, int);
void operator()(char const *, int i = 2, int j = 3);
void operator()(...);
};
INVOKE(&S::f, S(), 3.5)
are (S &&, double const &)
.INVOKE(S(), 1, 2)
are (int, int)
.INVOKE(S(), "abc", 5)
are (const char *, int)
.
The defaulted parameter j
does not correspond to an argument.INVOKE(S(), locale(), 5)
are (locale, int)
.
Arguments corresponding to ellipsis maintain their types.Template | Condition | Comments |
---|---|---|
template <class Fn, class... ArgTypes>
|
Fn and all types in the parameter pack ArgTypes
shall be complete types, (possibly cv-qualified) void , or arrays of unknown bound.
|
see below |
template <class Fn, class... ArgTypes>
|
Fn and all types in the parameter pack ArgTypes
shall be complete types, (possibly cv-qualified) void ,
or arrays of unknown bound.
|
see below |
Access checking is performed as if in a context unrelated to Fn
and ArgTypes
.
Only the validity of the immediate context of the expression is considered.
The member raw_invocation_type<Fn(ArgTypes...)>::type
shall be defined as follows.
If the expression INVOKE(declval<Fn>(), declval<ArgTypes>()...)
is ill-formed when treated as an unevaluated operand (type
. Otherwise:
R
denote result_of_t<Fn(ArgTypes...)>
.Ti
be the INVOKE(declval<Fn>(), declval<ArgTypes>()...)
.type
shall name the function type R(T1, T2, ...)
.
The member invocation_type<Fn(ArgTypes...)>::type
shall be defined as follows.
If raw_invocation_type<Fn(ArgTypes...)>::type
does not exist, there shall be no member type
.
Otherwise:
A1, A2,
… denote ArgTypes...
R(T1, T2, …)
denote raw_invocation_type_t<Fn(ArgTypes...)>
type
shall name the function type R(U1, U2, …)
where Ui
is decay_t<Ai>
if declval<Ai>()
is an rvalue
otherwise Ti
.
struct nonesuch {
~nonesuch() = delete;
nonesuch(nonesuch const&) = delete;
void operator=(nonesuch const&) = delete;
};
nonesuch
has no default constructor
(
template <class Default, class AlwaysVoid,
template<class...> class Op, class... Args>
struct DETECTOR { // exposition only
using value_t = false_type;
using type = Default;
};
template <class Default, template<class...> class Op, class... Args>
struct DETECTOR<Default, void_t<Op<Args...>>, Op, Args...> { // exposition only
using value_t = true_type;
using type = Op<Args...>;
};
template <template<class...> class Op, class... Args>
using is_detected = typename DETECTOR<nonesuch, void, Op, Args...>::value_t;
template <template<class...> class Op, class... Args>
using detected_t = typename DETECTOR<nonesuch, void, Op, Args...>::type;
template <class Default, template<class...> class Op, class... Args>
using detected_or = DETECTOR<Default, void, Op, Args...>;
// archetypal helper alias for a copy assignment operation:
template <class T>
using copy_assign_t = decltype(declval<T&>() = declval<T const &>());
// plausible implementation for the is_assignable type trait:
template <class T>
using is_copy_assignable = is_detected<copy_assign_t, T>;
// plausible implementation for an augmented is_assignable type trait
// that also checks the return type:
template <class T>
using is_canonical_copy_assignable = is_detected_exact<T&, copy_assign_t, T>;
— end example ]
// archetypal helper alias for a particular type member:
template <class T>
using diff_t = typename T::difference_type;
// alias the type member, if it exists, otherwise alias ptrdiff_t:
template <class Ptr>
using difference_type = detected_or_t<ptrdiff_t, diff_t, Ptr>;
— end example ]
<experimental/functional>
synopsis#include <functional>
namespace std {
namespace experimental::inline fundamentals_v3 {
// 7.2, Class template function
template<class> class function; // not defined
template<class R, class... ArgTypes> class function<R(ArgTypes...)>;
template<class R, class... ArgTypes>
void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
template<class R, class... ArgTypes>
bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
} // namespace experimental::inline fundamentals_v3
} // namespace std
function
The specification of all declarations within subclause std::experimental::function
uses
std::bad_function_call
, there is no additional type std::experimental::bad_function_call
— end note ]
namespace std {
namespace experimental::inline fundamentals_v3 {
template<class> class function; // undefined
template<class R, class... ArgTypes>
class function<R(ArgTypes...)> {
public:
using result_type = R;
using allocator_type = std::pmr::polymorphic_allocator<>;
function() noexcept;
function(nullptr_t) noexcept;
function(const function&);
function(function&&);
template<class F> function(F);
function(allocator_arg_t, const allocator_type&) noexcept;
function(allocator_arg_t, const allocator_type&, nullptr_t) noexcept;
function(allocator_arg_t, const allocator_type&, const function&);
function(allocator_arg_t, const allocator_type&, function&&);
template<class F> function(allocator_arg_t, const allocator_type&, F);
function& operator=(const function&);
function& operator=(function&&);
function& operator=(nullptr_t) noexcept;
template<class F> function& operator=(F&&);
template<class F> function& operator=(reference_wrapper<F>);
~function();
void swap(function&);
explicit operator bool() const noexcept;
R operator()(ArgTypes...) const;
const type_info& target_type() const noexcept;
template<class T> T* target() noexcept;
template<class T> const T* target() const noexcept;
allocator_type get_allocator() const noexcept;
};
template <class R, class... ArgTypes>
function(R(*)(ArgTypes...)) -> function<R(ArgTypes...)>;
template<class F>
function(F) -> function<see below>;
} // namespace experimental::inline fundamentals_v3
} // namespace std
A function object stores an allocator object of type std::pmr::polymorphic_allocator<>
,
which it uses to allocate memory for its internal data structures.
In the function
constructors, the allocator is initialized
(before the target object, if any) as follows:
f.get_allocator()
, where f
is the
parameter of the constructor.
allocator_arg_t
,
the allocator is initialized from the second parameter.
In all cases, the allocator of a parameter having type function&&
is unchanged.
If the constructor creates a target object, that target object is initialized
by uses-allocator construction with the allocator and other target object constructor arguments.
experimental::function&&
has an allocator equal to that of the object being constructed,
the implementation can often transfer ownership of the target rather than constructing a new one.
— end note ]
The deduction guide template<class F> function(F) -> function<see below>;
is specified in
function& operator=(const function& f);
function(allocator_arg, get_allocator(), f).swap(*this);
*this
.function& operator=(function&& f);
function(allocator_arg, get_allocator(), std::move(f)).swap(*this);
*this
.function& operator=(nullptr_t) noexcept;
*this != nullptr
, destroys the target of this
.!(*this)
.
*this
.template<class F> function& operator=(F&& f);
declval<decay_t<F>&>()
is ArgTypes...
and return type R
.
function(allocator_arg, get_allocator(), std::forward<F>(f)).swap(*this);
*this
.template<class F> function& operator=(reference_wrapper<F> f) noexcept;
function(allocator_arg, get_allocator(), f).swap(*this);
*this
.void swap(function& other);
this->get_allocator() == other.get_allocator()
.*this
and other
.*this
and other
are not interchanged.allocator_type get_allocator() const noexcept;
#include <memory>
namespace std {
namespace experimental::inline fundamentals_v3 {
// 8.2, Non-owning (observer) pointers
template <class W> class observer_ptr;
// 8.2.6, observer_ptr specialized algorithms
template <class W>
void swap(observer_ptr<W>&, observer_ptr<W>&) noexcept;
template <class W>
observer_ptr<W> make_observer(W*) noexcept;
// (in)equality operators
template <class W1, class W2>
bool operator==(observer_ptr<W1>, observer_ptr<W2>);
template <class W1, class W2>
bool operator!=(observer_ptr<W1>, observer_ptr<W2>);
template <class W>
bool operator==(observer_ptr<W>, nullptr_t) noexcept;
template <class W>
bool operator!=(observer_ptr<W>, nullptr_t) noexcept;
template <class W>
bool operator==(nullptr_t, observer_ptr<W>) noexcept;
template <class W>
bool operator!=(nullptr_t, observer_ptr<W>) noexcept;
// ordering operators
template <class W1, class W2>
bool operator<(observer_ptr<W1>, observer_ptr<W2>);
template <class W1, class W2>
bool operator>(observer_ptr<W1>, observer_ptr<W2>);
template <class W1, class W2>
bool operator<=(observer_ptr<W1>, observer_ptr<W2>);
template <class W1, class W2>
bool operator>=(observer_ptr<W1>, observer_ptr<W2>);
} // namespace experimental::inline fundamentals_v3
// 8.2.7, observer_ptr hash support
template <class T> struct hash;
template <class T> struct hash<experimental::observer_ptr<T>>;
} // namespace std
observer_ptr
overviewnamespace std::experimental::inline fundamentals_v3 {
template <class W> class observer_ptr {
using pointer = add_pointer_t<W>; // exposition-only
using reference = add_lvalue_reference_t<W>; // exposition-only
public:
// publish our template parameter and variations thereof
using element_type = W;
// 8.2.2, observer_ptr constructors
// default constructor
constexpr observer_ptr() noexcept;
// pointer-accepting constructors
constexpr observer_ptr(nullptr_t) noexcept;
constexpr explicit observer_ptr(pointer) noexcept;
// copying constructors (in addition to the implicit copy constructor)
template <class W2> constexpr observer_ptr(observer_ptr<W2>) noexcept;
// 8.2.3, observer_ptr observers
constexpr pointer get() const noexcept;
constexpr reference operator*() const;
constexpr pointer operator->() const noexcept;
constexpr explicit operator bool() const noexcept;
// 8.2.4, observer_ptr conversions
constexpr explicit operator pointer() const noexcept;
// 8.2.5, observer_ptr modifiers
constexpr pointer release() noexcept;
constexpr void reset(pointer = nullptr) noexcept;
constexpr void swap(observer_ptr&) noexcept;
}; // observer_ptr<>
} // namespace std::experimental::inline fundamentals_v3
A non-owning pointer, known as an observer, is an object o
that stores a pointer to a second object, w
.
In this context, w
is known as a watched object.
nullptr
.
— end note ]
o
and w
.
Specializations of observer_ptr
shall meet the requirements
of a W
of an observer_ptr
shall not be a reference type, but may be an incomplete type.
observer_ptr
include clarity of interface specification in new code,
and interoperability with pointer-based legacy code.
— end note ]
observer_ptr
constructorsconstexpr observer_ptr() noexcept; constexpr observer_ptr(nullptr_t) noexcept;
get() == nullptr
.constexpr explicit observer_ptr(pointer other) noexcept;
get() == other
.template <class W2> constexpr observer_ptr(observer_ptr<W2> other) noexcept;
W2*
is convertible to W*
.get() == other.get()
.observer_ptr
observersconstexpr pointer get() const noexcept;
constexpr reference operator*() const;
get() != nullptr
is true
.*get()
.constexpr pointer operator->() const noexcept;
get()
.constexpr explicit operator bool() const noexcept;
get() != nullptr
.observer_ptr
conversionsconstexpr explicit operator pointer() const noexcept;
get()
.observer_ptr
modifiersconstexpr pointer release() noexcept;
get() == nullptr
.get()
had at the start of the call to release
.constexpr void reset(pointer p = nullptr) noexcept;
get() == p
.constexpr void swap(observer_ptr& other) noexcept;
swap
on the stored pointers of *this
and other
.observer_ptr
specialized algorithmstemplate <class W>
void swap(observer_ptr<W>& p1, observer_ptr<W>& p2) noexcept;
p1.swap(p2)
.template <class W> observer_ptr<W> make_observer(W* p) noexcept;
observer_ptr<W>{p}
.template <class W1, class W2>
bool operator==(observer_ptr<W1> p1, observer_ptr<W2> p2);
p1.get() == p2.get()
.template <class W1, class W2>
bool operator!=(observer_ptr<W1> p1, observer_ptr<W2> p2);
not (p1 == p2)
.template <class W>
bool operator==(observer_ptr<W> p, nullptr_t) noexcept; template <class W>
bool operator==(nullptr_t, observer_ptr<W> p) noexcept;
not p
.template <class W>
bool operator!=(observer_ptr<W> p, nullptr_t) noexcept; template <class W>
bool operator!=(nullptr_t, observer_ptr<W> p) noexcept;
(bool)p
.template <class W1, class W2>
bool operator<(observer_ptr<W1> p1, observer_ptr<W2> p2);
less<W3>()(p1.get(), p2.get())
,
where W3
is the composite pointer type (W1*
and W2*
.
template <class W1, class W2>
bool operator>(observer_ptr<W1> p1, observer_ptr<W2> p2);
p2 < p1
.template <class W1, class W2>
bool operator<=(observer_ptr<W1> p1, observer_ptr<W2> p2);
not (p2 < p1)
.template <class W1, class W2>
bool operator>=(observer_ptr<W1> p1, observer_ptr<W2> p2);
not (p1 < p2)
.observer_ptr
hash supporttemplate <class T> struct hash<experimental::observer_ptr<T>>;
The specialization is enabled (p
of type observer_ptr<T>
,
hash<observer_ptr<T>>()(p)
evaluates to the same value as hash<T*>()(p.get())
.
<experimental/memory_resource>
synopsisnamespace std::pmr::experimental::inline fundamentals_v3 {
// The name resource_adaptor_imp is for exposition only.
template <class Allocator> class resource_adaptor_imp;
template <class Allocator>
using resource_adaptor = resource_adaptor_imp<
typename allocator_traits<Allocator>::template rebind_alloc<char>>;
} // namespace std::pmr::experimental::inline fundamentals_v3
resource_adaptor
resource_adaptor
An instance of resource_adaptor<Allocator>
is an adaptor that wraps a memory_resource
interface around Allocator
.
In order that resource_adaptor<X<T>>
and resource_adaptor<X<U>>
are the same type for any allocator template X
and types T
and U
,
resource_adaptor<Allocator>
is rendered as an alias to a class template such that Allocator
is rebound to a char
value type in every specialization of the class template.
The requirements on this class template are defined below.
The name resource_adaptor_imp
is for exposition only and is not normative,
but the definitions of the members of that class, whatever its name, are normative.
In addition to the resource_adaptor
shall meet the following additional requirements:
typename allocator_traits<Allocator>::pointer
shall be identical to typename allocator_traits<Allocator>::value_type*
.typename allocator_traits<Allocator>::const_pointer
shall be identical to typename allocator_traits<Allocator>::value_type const*
.typename allocator_traits<Allocator>::void_pointer
shall be identical to void*
.typename allocator_traits<Allocator>::const_void_pointer
shall be identical to void const*
.
// The name resource_adaptor_imp is for exposition only.
template <class Allocator>
class resource_adaptor_imp : public memory_resource {
// for exposition only
Allocator m_alloc;
public:
using allocator_type = Allocator;
resource_adaptor_imp() = default;
resource_adaptor_imp(const resource_adaptor_imp&) = default;
resource_adaptor_imp(resource_adaptor_imp&&) = default;
explicit resource_adaptor_imp(const Allocator& a2);
explicit resource_adaptor_imp(Allocator&& a2);
resource_adaptor_imp& operator=(const resource_adaptor_imp&) = default;
allocator_type get_allocator() const { return m_alloc; }
protected:
virtual void* do_allocate(size_t bytes, size_t alignment);
virtual void do_deallocate(void* p, size_t bytes, size_t alignment);
virtual bool do_is_equal(const memory_resource& other) const noexcept;
};
template <class Allocator>
using resource_adaptor = typename resource_adaptor_imp<
typename allocator_traits<Allocator>::template rebind_alloc<char>>;
resource_adaptor_imp
constructorsexplicit resource_adaptor_imp(const Allocator& a2);
m_alloc
with a2
.explicit resource_adaptor_imp(Allocator&& a2);
m_alloc
with std::move(a2)
.resource_adaptor_imp
member functionsvoid* do_allocate(size_t bytes, size_t alignment);
m_alloc.allocate
.
The size and alignment of the allocated memory shall meet the requirements
for a class derived from memory_resource
(void do_deallocate(void* p, size_t bytes, size_t alignment);
p
was previously allocated using A.allocate
, where A == m_alloc
, and not subsequently deallocated.m_alloc.deallocate()
.bool do_is_equal(const memory_resource& other) const noexcept;
Let p
be dynamic_cast<const resource_adaptor_imp*>(&other)
.
false
if p
is null, otherwise the value of m_alloc == p->m_alloc
.<experimental/iterator>
synopsis#include <iterator>
namespace std::experimental::inline fundamentals_v3 {
// 9.2, Class template ostream_joiner
template <class DelimT, class charT = char, class traits = char_traits<charT>>
class ostream_joiner;
template <class charT, class traits, class DelimT>
ostream_joiner<decay_t<DelimT>, charT, traits>
make_ostream_joiner(basic_ostream<charT, traits>& os, DelimT&& delimiter);
} // namespace std::experimental::inline fundamentals_v3
ostream_joiner
ostream_joiner
writes (using operator<<
) successive elements onto the output stream from which it was constructed.
The delimiter that it was constructed with is written to the stream between every two T
s that are written.
It is not possible to get a value out of the output iterator.
Its only use is as an output iterator in situations like
while (first != last)
*result++ = *first++;
ostream_joiner
is defined as
namespace std::experimental::inline fundamentals_v3 {
template <class DelimT, class charT = char, class traits = char_traits<charT>>
class ostream_joiner {
public:
using char_type = charT;
using traits_type = traits;
using ostream_type = basic_ostream<charT, traits>;
using iterator_category = output_iterator_tag;
using value_type = void;
using difference_type = void;
using pointer = void;
using reference = void;
ostream_joiner(ostream_type& s, const DelimT& delimiter);
ostream_joiner(ostream_type& s, DelimT&& delimiter);
template<typename T>
ostream_joiner& operator=(const T& value);
ostream_joiner& operator*() noexcept;
ostream_joiner& operator++() noexcept;
ostream_joiner& operator++(int) noexcept;
private:
ostream_type* out_stream; // exposition only
DelimT delim; // exposition only
bool first_element; // exposition only
};
} // namespace std::experimental::inline fundamentals_v3
ostream_joiner(ostream_type& s, const DelimT& delimiter);
out_stream
with std::addressof(s)
,
delim
with delimiter
,
and first_element
with true
.
ostream_joiner(ostream_type& s, DelimT&& delimiter);
out_stream
with std::addressof(s)
,
delim
with move(delimiter)
,
and first_element
with true
.
template<typename T>
ostream_joiner& operator=(const T& value);
if (!first_element)
*out_stream << delim;
first_element = false;
*out_stream << value;
return *this;
ostream_joiner& operator*() noexcept;
*this
.ostream_joiner& operator++() noexcept; ostream_joiner& operator++(int) noexcept;
*this
.template <class charT, class traits, class DelimT>
ostream_joiner<decay_t<DelimT>, charT, traits>
make_ostream_joiner(basic_ostream<charT, traits>& os, DelimT&& delimiter);
ostream_joiner<decay_t<DelimT>, charT, traits>(os, forward<DelimT>(delimiter));
<experimental/algorithm>
synopsis#include <algorithm>
namespace std::experimental::inline fundamentals_v3 {
// 10.2, Sampling
template<class PopulationIterator, class SampleIterator, class Distance>
SampleIterator sample(PopulationIterator first, PopulationIterator last,
SampleIterator out, Distance n);
// 10.3, Shuffle
template<class RandomAccessIterator>
void shuffle(RandomAccessIterator first, RandomAccessIterator last);
} // namespace std::experimental::inline fundamentals_v3
template<class PopulationIterator, class SampleIterator, class Distance>
SampleIterator sample(PopulationIterator first, PopulationIterator last,
SampleIterator out, Distance n);
return ::std::sample(first, last, out, n, g);
where g
denotes
the per-thread engine (g
serves as the
implementation’s source of randomness.
template<class RandomAccessIterator>
void shuffle(RandomAccessIterator first, RandomAccessIterator last);
RandomAccessIterator
meets the
[first,last)
such that each possible permutation of those elements has equal
probability of appearance.(last - first) - 1
swaps.<experimental/random>
synopsis#include <random>
namespace std::experimental::inline fundamentals_v3 {
// 11.1.2, Function template randint
template <class IntType>
IntType randint(IntType a, IntType b);
void reseed();
void reseed(default_random_engine::result_type value);
} // namespace std::experimental::inline fundamentals_v3
randint
A separate per-thread engine of type default_random_engine
(
template<class IntType>
IntType randint(IntType a, IntType b);
IntType
in a
≤ b
.a
≤ i ≤ b
,
produced from a thread-local instance of uniform_int_distribution<IntType>
(void reseed(); void reseed(default_random_engine::result_type value);
g
be the per-thread engine. The first
form sets g
to an unpredictable state. The second form
invokes g.seed(value)
.randint
do not
depend on values produced by g
before calling reseed
.
reseed
also resets any instances of uniform_int_distribution
used by randint
.
— end note ]