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### 300. list::merge() specification incomplete

Section: 24.3.10.5 [list.ops] Status: CD1 Submitter: John Pedretti Opened: 2001-01-23 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

The "Effects" clause for list::merge() (24.3.10.5 [list.ops], p23) appears to be incomplete: it doesn't cover the case where the argument list is identical to *this (i.e., this == &x). The requirement in the note in p24 (below) is that x be empty after the merge which is surely unintended in this case.

Proposed resolution:

In 24.3.10.5 [list.ops], replace paragraps 23-25 with:

> 23 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.

> 24 Notes: Stable: if (&x != this), then for equivalent elements in the two original ranges, the elements from the original range [begin(), end()) always precede the elements from the original range [x.begin(), x.end()). If (&x != this) the range [x.begin(), x.end()) is empty after the merge.

> 25 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.

[Copenhagen: The original proposed resolution did not fix all of the problems in 24.3.10.5 [list.ops], p22-25. Three different paragraphs (23, 24, 25) describe the effects of `merge`. Changing p23, without changing the other two, appears to introduce contradictions. Additionally, "merges the argument list into the list" is excessively vague.]

[Post-Curaçao: Robert Klarer provided new wording.]