P2968R2 Make `std::ignore` A First-Class Object

[frederick-vs-ja]

WG21-P2968R2 Make std::ignore A First-Class Object

No feature-test macro is mentioned.

We're already conforming to the improved specification (except for the location of std::ignore).

STL/stl/inc/tuple

Lines 122 to 130 in 165fc94

	struct _Ignore { // struct that ignores assignments
	template <class _Ty>
	constexpr const _Ignore& operator=(const _Ty&) const noexcept /* strengthened */ {
	// do nothing
	return *this;
	}
	};
	_EXPORT_STD _INLINE_VAR constexpr _Ignore ignore{};

So the only things need to be done are

• moving _Ignore and ignore to <utility>,
• removing the /* strengthened */ comment from the operator=, and
• adding the // P2968R2 Make std::ignore A First-Class Object comment to <yvals_core.h> immediately after this line
  

  STL/stl/inc/yvals_core.h

  Line 81 in 165fc94

  // P2937R0 Freestanding Library: Remove strtok

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[cpplearner]

WG21-P2968R2 requires std::ignore to be available when <utility> is included, which isn't currently the case with MSVC STL.

To implement this, we should move the definition of std::ignore to <utility>.

(Aside: this movement is safe because <tuple> unconditionally includes <__msvc_iter_core.hpp>, which unconditionally includes <utility>.)