P0472R3 Put `monostate` In `<utility>`

[StephanTLavavej]

WG21-P0472R3 Put monostate In <utility>

No feature-test macro is mentioned.

We can accept PRs to implement this backward-compatible change unconditionally.

[yehudamber]

Hi, I would like to work on this.
Just a question: monostate is currently defined in xutility, and its relational operators and std::hash specialization are defined in variant itself. All of those still have to be available when including <variant>. How make them available in both variant and utility (move them to a new header/move them to xutility and include it from utility/other)?

[frederick-vs-ja]

Hi, I would like to work on this.
Just a question: monostate is currently defined in xutility, and its relational operators and std::hash specialization are defined in variant itself. All of those still have to be available when including <variant>. How make them available in both variant and utility (move them to a new header/move them to xutility and include it from utility/other)?

Thanks! In MSVC STL <variant> transitively includes <utility>, so this shouldn't be a problem.

STL/stl/inc/variant

Line 20 in f2a2933

#include <utility>

[yehudamber]

One more question: is it OK to put monostate in <utility> in all language modes, or do I have to limit it to C++26?

[frederick-vs-ja]

One more question: is it OK to put monostate in <utility> in all language modes, or do I have to limit it to C++26?

I think maintainers tend to accept the changes in "all modes" (of course, since C++17).