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2894. The function templatestd::apply() is required to beconstexpr, butstd::invoke() isn't

Section: 22.10.5[func.invoke]Status:ResolvedSubmitter: Great BritainOpened: 2017-02-03Last modified: 2020-09-06

Priority:3

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Discussion:

The function templatestd::apply() in 22.4.6[tuple.apply] is required to beconstexpr, butstd::invoke() in 22.10.5[func.invoke] isn't. The most sensible implementation ofapply_impl() is exactly equivalent tostd::invoke(), so this requires implementations to have aconstexpr version ofinvoke() for internal use, and the public APIstd::invoke, which must not beconstexpr even though it is probably implemented in terms of the internal version.

Proposed change: Addconstexpr tostd::invoke.

[2017-02-20, Marshall adds wording]

[Kona 2017-03-01]

We think this needsCWG 1581 to work; accepted as Immediate to resolve NB comment.

Friday: CWG 1581 was not moved in Kona. Status back to Open.

[2017-07 Toronto Tuesday PM issue prioritization]

Priority 3

[2020-01 Resolved by the adoption ofP1065 in Cologne.]

Proposed resolution:

This wording is relative toN4640.

1. Modify 22.10.5[func.invoke] as indicated:

   template <class F, class... Args>constexpr result_of_t<F&&(Args&&...)> invoke(F&& f, Args&&... args);