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Section: 18.104.22.168 [list.ops] Status: C++11 Submitter: Pablo Halpern Opened: 2009-09-24 Last modified: 2019-01-01
Priority: Not Prioritized
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In Bellevue (I think), we passed N2525, which, among other things, specifies that the behavior of list::splice is undefined if the allocators of the two lists being spliced do not compare equal. The same rationale should apply to list::merge. The intent of list::merge (AFAIK) is to move nodes from one sorted list into another sorted list without copying the elements. This is possible only if the allocators compare equal.
Relative to the August 2009 WP, N2857, change 22.214.171.124 [list.ops], paragraphs 22-25 as follows:
void merge(list&& x); template <class Compare> void merge(list&& x, Compare comp);
Requires: both the list and the argument list shall be sorted according to operator< or comp.
Effects: If (&x == this) does nothing; otherwise, merges the two sorted ranges [begin(), end()) and [x.begin(), x.end()). The result is a range in which the elements will be sorted in non-decreasing order according to the ordering defined by comp; that is, for every iterator i, in the range other than the first, the condition comp(*i, *(i - 1) will be false.
Remarks: Stable. If (&x != this) the range [x.begin(), x.end()) is empty after the merge.
Complexity: At most size() + x.size() - 1 applications of comp if (&x != this); otherwise, no applications of comp are performed. If an exception is thrown other than by a comparison there are no effects.