[libc++] P2255R2: Changes to Standard library components - `INVOKE`

[Zingam]

• INVOKE
  • 20.14.4 [func.require]

[frederick-vs-ja]

I've roughly checked necessary changes and possibly resolutions.

• is_(nothrow_)invocable_r(_v)
  • perhaps we want to update __invokable_r together
• invoke_r
  • in libc++, it will be automatically updated by changes of is_invocable_r_v, but it might be wanted to update __invoke_r together
• operator() of result types of bind<R>
  • update constraints of __bind_r::operator(), perhaps
• operator() of result types of and visit<R>
  • add static_assert to __value_visitor_return_type::operator() or use __invoke_r?
• constraints on constructors of function, move_only_function, and copyable_function
  • seems better to reuse __invokable_r for function
• packaged_task::operator() and packaged_task::make_ready_at_thread_exit
  • add static_assert to __packaged_task_func::operator() of use __invoke_r?

[H-G-Hristov]

@frederick-vs-ja Thank you for the research. I wonder if it makes sense to split this into further items/sub-issues?
BTW. Are you interested in working on any items in P2255?

[H-G-Hristov]

WIP Notes:

• INVOKE<R> https://eel.is/c++draft/func.require#2
  • invoke_r()
    • https://eel.is/c++draft/func.invoke
  • operator()
    • https://eel.is/c++draft/function.objects#func.wrap.func.inv-1
    • https://eel.is/c++draft/function.objects#func.wrap.move.inv-3