This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of C++11 status.
Section: 16.3.2.4 [structure.specifications] Status: C++11 Submitter: Thomas Plum Opened: 2009-03-03 Last modified: 2016-01-28
Priority: Not Prioritized
View other active issues in [structure.specifications].
View all other issues in [structure.specifications].
View all issues with C++11 status.
Discussion:
Addresses UK-163 [CD1]
Many functions are defined as "Effects: Equivalent to a...", which seems to also define the preconditions, effects, etc. But this is not made clear.
After studying the occurrences of "Effects: Equivalent to", I agree with the diagnosis but disagree with the solution. In 23.4.3.3 [string.cons] we find
14 Effects: If InputIterator is an integral type, equivalent to basic_string(static_cast<size_type>(begin), static_cast<value_type>(end), a)
15 Otherwise constructs a string from the values in the range [begin, end), as indicated in the Sequence Requirements table (see 23.1.3).
This would be devishly difficult to re-write with an explicit "Equivalent to:" clause. Instead, I propose the following, which will result in much less editorial re-work.
[ 2009-05-09 Alisdair adds: ]
This issue is related to 492.
[ Batavia (2009-05): ]
We agree with the proposed resolution. Move to Tentatively Ready.
Proposed resolution:
Add a new paragraph after 16.3.2.4 [structure.specifications], p3:
-3- Descriptions of function semantics contain the following elements (as appropriate):154
- Requires: the preconditions for calling the function
- Effects: the actions performed by the function
- Postconditions: the observable results established by the function
- Returns: a description of the value(s) returned by the function
- Throws: any exceptions thrown by the function, and the conditions that would cause the exception
- Complexity: the time and/or space complexity of the function
- Remarks: additional semantic constraints on the function
- Error conditions: the error conditions for error codes reported by the function.
- Notes: non-normative comments about the function
Whenever the Effects element specifies that the semantics of some function F are Equivalent to some code-sequence, then the various elements are interpreted as follows. If F's semantics specifies a Requires element, then that requirement is logically imposed prior to the equivalent-to semantics. Then, the semantics of the code-sequence are determined by the Requires, Effects, Postconditions, Returns, Throws, Complexity, Remarks, Error Conditions and Notes specified for the (one or more) function invocations contained in the code-sequence. The value returned from F is specified by F's Returns element, or if F has no Returns element, a non-void return from F is specified by the Returns elements in code-sequence. If F's semantics contains a Throws (or Postconditions, or Complexity) element, then that supersedes any occurrences of that element in the code-sequence.