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1231.weak_ptr comparisons incompletely resolved

Section: 20.3.2.3.6[util.smartptr.weak.obs]Status:C++11Submitter: Daniel KrüglerOpened: 2009-10-10Last modified: 2016-01-28

Priority:Not Prioritized

View all otherissues in [util.smartptr.weak.obs].

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Discussion:

Then2637paper suggested several updates of the ordering semantics ofshared_ptrandweak_ptr, among those the explicit comparison operators ofweak_ptr wereremoved/deleted, instead a corresponding functorowner_less was added.The problem is thatn2637did not clearly enough specify, how the previous wording parts describingthe comparison semantics ofweak_ptr should be removed.

[2009-11-06 Howard adds:]

Moved to Tentatively Ready after 5 positive votes on c++std-lib.

Proposed resolution:

1. Change 20.3.2.3[util.smartptr.weak]/2 as described, the intention is to fixthe now no longer valid requirement thatweak_ptr isLessComparable [Note the deleted comma]:

   Specializations ofweak_ptr shall beCopyConstructible,andCopyAssignable,andLessThanComparable, allowing their use in standard containers.

2. In 20.3.2.3.6[util.smartptr.weak.obs] remove the paragraphs 9-11 including prototype:

   template<class T, class U> bool operator<(const weak_ptr<T>& a, const weak_ptr<U>& b);

   Returns: an unspecified value such that

   • operator< is a strict weak ordering as described in 25.4;
   • under the equivalence relation defined byoperator<,!(a< b) && !(b < a), twoweak_ptr instances areequivalent if and only if they share ownership or are both empty.

   Throws: nothing.

   [Note: Allowsweak_ptr objects to be used as keys in associativecontainers. —end note]