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Section: 20.4 [pairs] Status: C++11 Submitter: Martin Sebor Opened: 2001-01-14 Last modified: 2016-02-10
Priority: Not Prioritized
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The synopsis of the header <utility> in 20.2 [utility] lists the complete set of equality and relational operators for pair but the section describing the template and the operators only describes operator==() and operator<(), and it fails to mention any requirements on the template arguments. The remaining operators are not mentioned at all.
[ 2009-09-27 Alisdair reopens. ]
The issue is a lack of wording specifying the semantics of std::pair relational operators. The rationale is that this is covered by catch-all wording in the relops component, and that as relops directly precedes pair in the document this is an easy connection to make.
Reading the current working paper I make two observations:
- relops no longer immediately precedes pair in the order of specification. However, even if it did, there is a lot of pair specification itself between the (apparently) unrelated relops and the relational operators for pair. (The catch-all still requires operator== and operator< to be specified explicitly)
- No other library component relies on the catch-all clause. The following all explicitly document all six relational operators, usually in a manner that could have deferred to the relops clause.tuple unique_ptr duration time_point basic_string queue stack move_iterator reverse_iterator regex submatch thread::id
The container components provide their own (equivalent) definition in 22.2.1 [container.requirements.general] Table 90 -- Container requirements and do so do not defer to relops.
Shared_ptr explicitly documents operator!= and does not supply the other 3 missing operators (>,>=,<=) so does not meet the reqirements of the relops clause.
Weak_ptr only supports operator< so would not be covered by relops.
At the very least I would request a note pointing to the relops clause we rely on to provide this definition. If this route is taken, I would recommend reducing many of the above listed clauses to a similar note rather than providing redundant specification.
My preference would be to supply the 4 missing specifications consistent with the rest of the library.
[ 2009-10-11 Daniel opens 1233 which deals with the same issue as it pertains to unique_ptr. ]
[ 2009-10 Santa Cruz: ]
Move to Ready
After p20 20.4 [pairs] add:
template <class T1, class T2> bool operator!=(const pair<T1,T2>& x, const pair<T1,T2>& y);
Returns: !(x==y)template <class T1, class T2> bool operator> (const pair<T1,T2>& x, const pair<T1,T2>& y);
Returns: y < xtemplate <class T1, class T2> bool operator>=(const pair<T1,T2>& x, const pair<T1,T2>& y);
Returns: !(x < y)template <class T1, class T2> bool operator<=(const pair<T1,T2>& x, const pair<T1,T2>& y);
Returns: !(y < x)
188.8.131.52 [operators] paragraph 10 already specifies the semantics. That paragraph says that, if declarations of operator!=, operator>, operator<=, and operator>= appear without definitions, they are defined as specified in 184.108.40.206 [operators]. There should be no user confusion, since that paragraph happens to immediately precede the specification of pair.