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2151.basic_string<>::swap semantics ignore allocators

Section: 27.4.3.2[string.require]Status:ResolvedSubmitter: Robert ShearerOpened: 2012-04-13Last modified: 2018-11-25

Priority:3

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Discussion:

In C++11,basic_string is not described as a "container", and is not governed by the allocator-aware container semantics described in sub-clause 23.2[container.requirements]; as a result, and requirements or contracts for thebasic_string interface must be documented in Clause 27[strings].

Sub-clause 27.4.3.7.8[string.swap] defines theswap member function with no requirements, andwith guarantees to execute in constant time without throwing. Fulfilling such a contract is not reasonable in the presence of unequal non-propagating allocators.

In contrast, 23.2.2[container.requirements.general] p7 declares the behavior of memberswap for containers with unequal non-propagating allocators to be undefined.

Resolution proposal:

Additional language from Clause 23[containers] should probably be copied to Clause 27[strings]. I will refrain from an exactly recommendation, however, as I am raising furtherissues related to the language in Clause 23[containers].

[2013-03-15 Issues Teleconference]

Moved to Open.

Alisdair has offered to provide wording.

Telecon notes that 23.2.2[container.requirements.general]p13 says thatstring is anallocator-aware container.

Resolved by the adoption ofP1148 in San Diego.

Proposed resolution: