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### 2151. `basic_string<>::swap` semantics ignore allocators

Section: 21.3.3.2 [string.require] Status: Resolved Submitter: Robert Shearer Opened: 2012-04-13 Last 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 22.2 [container.requirements]; as a result, and requirements or contracts for the `basic_string` interface must be documented in Clause 21 [strings].

Sub-clause 21.3.3.7.8 [string.swap] defines the `swap` member function with no requirements, and with 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, 22.2.1 [container.requirements.general] p7 declares the behavior of member `swap` for containers with unequal non-propagating allocators to be undefined.

Resolution proposal:

Additional language from Clause 22 [containers] should probably be copied to Clause 21 [strings]. I will refrain from an exactly recommendation, however, as I am raising further issues related to the language in Clause 22 [containers].

[2013-03-15 Issues Teleconference]

Moved to Open.

Alisdair has offered to provide wording.

Telecon notes that 22.2.1 [container.requirements.general]p13 says that `string` is an allocator-aware container.

Resolved by the adoption of P1148 in San Diego.

Proposed resolution: