LWG2095 and LWG3003: allocator-extended constructors for std::promise

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ISO/IEC JTC1 SC22 WG21 paper scheduling and management

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LWG2095 and LWG3003: allocator-extended constructors for std::promise #1580

Open jwakely opened 1 year ago

jwakely commented 1 year ago

https://cplusplus.github.io/LWG/issue2095 https://cplusplus.github.io/LWG/issue3003

These two issues suggest two contradictory changes to std::promise. LWG would like LEWG to decide whether to add the missing constructors, or remove the existing allocator-extended constructors.

inbal2l commented 1 year ago

The issue was discussed in Library Evolution Telecon on 2023-07-25 Full Minutes.

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Next Steps

Jonathan will come back with a proposed resolution that aligns with Tim’s suggestion, LEWG will vote on the proposed resolution.

jwakely commented 3 weeks ago

Please see the updated proposed resolution for LWG3003, which would resolve both 3003 and 2095.

The new approach is:

Keep support for using an allocator for shared state of a promise.
Remove uses_allocator specialization for promise.
Restore support for using an allocator for the shared state of packaged_task.
Do not restore uses_allocator specialization for packaged_task.
Update packaged_task::reset() to deal with allocators.