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2110.remove can't swap but note says it might

Section: 26.7.8[alg.remove]Status:C++14Submitter: Howard HinnantOpened: 2011-12-07Last modified: 2016-01-28

Priority:Not Prioritized

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Discussion:

26.7.8[alg.remove]/p1 says:

1Requires: The type of*first shall satisfy theMoveAssignable requirements (Table 22).

This means thatremove/remove_if can only use move assignment to permute the sequence. But then 26.7.8[alg.remove]/p6 (non-normatively) contradicts p1:

6Note: each element in the range[ret,last), whereret is the returned value, has a valid but unspecified state, because the algorithms can eliminate elements by swapping with or moving from elements that were originally in that range.

[2012, Kona]

Move to Ready.

Alisdair notes we could extend permission to useswap if it is available, but thereis no interest. Accept the proposed resolution as written.

[2012, Portland: applied to WP]

Proposed resolution:

This wording is relative to the FDIS.

Change 26.7.8[alg.remove] as indicated:

template<class ForwardIterator, class T>  ForwardIterator remove(ForwardIterator first, ForwardIterator last,                         const T& value);template<class ForwardIterator, class Predicate>  ForwardIterator remove_if(ForwardIterator first, ForwardIterator last,                            Predicate pred);

[…]

-6-Note: each element in the range[ret,last), whereret is the returned value, has a valid but unspecified state, because the algorithms can eliminate elements byswapping with or moving from elements that were originally in that range.