[PATCH] D11329: [libcxx] Add __invoke_constexpr functions. Try 2.

[Eric Fiselier]

EricWF created this revision.
EricWF added a reviewer: mclow.lists.
EricWF added a subscriber: cfe-commits.

This patch is an alternate approach to D9730

std::experimental::apply requires a constexpr implementation of INVOKE(...). Simply marking the current implementation of __invoke as constexpr will break existing code due to CWG issue #1581. For this reason we should add a separate function called __invoke_constexpr to be used where constexpr is required.

This patch adds a `__invoke_constexpr` function that mirrors `__invoke`.

I chose not to generate invoke functions using macros because of the amount of code that would have to be within a macro block. It also is likely to yield bad error messages.

This patch also re-enables constexpr support for std::experimental::apply.

Also See:
https://llvm.org/bugs/show_bug.cgi?id=23141
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1581

http://reviews.llvm.org/D11329

Files:
  include/experimental/tuple
  include/type_traits
  test/std/experimental/utilities/tuple/tuple.apply/constexpr_types.pass.cpp

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