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3653.<coroutine> is freestanding, but usesstd::hash which is not

Section: 17.13.2[coroutine.syn]Status:NewSubmitter: Jonathan WakelyOpened: 2021-12-17Last modified: 2025-11-11

Priority:3

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Discussion:

The<coroutine> header is required for freestanding implementations, but it defines a specialization ofstd::hash, which is not required for freestanding implementations.

Presumably we should make thestd::hash specialization conditionally present.

[2022-01-30; Reflector poll]

Set priority to 3 after reflector poll.Would be resolved byP1642 for C++23,but it's still a defect in C++20.

[2025-11-11; Jonathan adds wording for C++20.]

This wording would resolve the defect for C++20,but the issue should be closed as Resolved in C++23.

Proposed resolution:

This wording is relative to ISO/IEC 14882:2020(E).

1. Modify 17.13.4.9[coroutine.handle.hash] as indicated:

   template<class P> struct hash<coroutine_handle<P>>;

   -1-The specialization is enabled (22.10.19[unord.hash])in a hosted implementation.