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2698. Effect ofassign() on iterators/pointers/references

Section: 23.2.4[sequence.reqmts]Status:C++17Submitter: Tim SongOpened: 2016-04-25Last modified: 2017-07-30

Priority:0

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Discussion:

The sequence container requirements table says nothing about the effect ofassign() on iterators, pointers or references into the container. Before LWG2209⁽ⁱ⁾ (and LWG320⁽ⁱ⁾ forstd::list),assign() was specified as "erase everything theninsert", which implies wholesale invalidation from the "erase everything" part. With that gone, the blanket "no invalidation" wording in 23.2.2[container.requirements.general]/12 would seem to apply, which makes absolutely no sense.

The proposed wording below simply spells out the invalidation rule implied by the previous "erase everything" wording.

[2016-05 Issues Telecon]

This is related to2256⁽ⁱ⁾

Proposed resolution:

This wording is relative to N4582.

1. In 23.2.4[sequence.reqmts], edit Table 107 (Sequence container requirements) as indicated:

   Table 107 — Sequence container requirements (in addition to container)

   Expression	Return type	Assertion/note pre-/post-condition
   […]
   a.assign(i, j)	void	Requires:T shall beEmplaceConstructible intoX from*i and assignable from*i. Forvector, if the iterator does not meet the forward iterator requirements (24.2.5), T shall also beMoveInsertable intoX. Each iterator in the range[i, j) shall be dereferenced exactly once. pre:i,j are not iterators intoa. Replaces elements ina with a copy of[i, j). Invalidates all references, pointers and iterators referring to the elements ofa. Forvector anddeque, also invalidates the past-the-end iterator.
   […]
   a.assign(n, t)	void	Requires:T shall beCopyInsertable intoX andCopyAssignable. pre:t is not a reference intoa. Replaces elements ina withn copies oft. Invalidates all references, pointers and iterators referring to the elements ofa. Forvector anddeque, also invalidates the past-the-end iterator.