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Implement P0472R3 - Put monostate in <utility> #5382

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Merged
merged 3 commits into from
Apr 10, 2025
Merged

Implement P0472R3 - Put monostate in <utility> #5382

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4d6c0e8
Implement P0472R3 - Move monostate to <utility>
yehudamber Mar 31, 2025
0463c5b
Add P0472R3 to the C++17 section of yvals_core.h.
StephanTLavavej Mar 31, 2025
c68bd23
Move hash<monostate> to <utility>
yehudamber Apr 1, 2025
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40 changes: 40 additions & 0 deletions stl/inc/utility
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Original file line number Diff line number Diff line change
Expand Up @@ -973,6 +973,46 @@ _NODISCARD _MSVC_INTRINSIC constexpr _Forward_like_t<_Ty, _Uty> forward_like(_Ut
}
#endif // _HAS_CXX23

#if _HAS_CXX17
_EXPORT_STD struct monostate {};

_EXPORT_STD _NODISCARD constexpr bool operator==(monostate, monostate) noexcept {
return true;
}

#if _HAS_CXX20
_EXPORT_STD _NODISCARD constexpr strong_ordering operator<=>(monostate, monostate) noexcept {
return strong_ordering::equal;
}
#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
_NODISCARD constexpr bool operator!=(monostate, monostate) noexcept {
return false;
}
_NODISCARD constexpr bool operator<(monostate, monostate) noexcept {
return false;
}
_NODISCARD constexpr bool operator>(monostate, monostate) noexcept {
return false;
}
_NODISCARD constexpr bool operator<=(monostate, monostate) noexcept {
return true;
}
_NODISCARD constexpr bool operator>=(monostate, monostate) noexcept {
return true;
}
#endif // ^^^ !_HAS_CXX20 ^^^

template <>
struct hash<monostate> {
using _ARGUMENT_TYPE_NAME _CXX17_DEPRECATE_ADAPTOR_TYPEDEFS = monostate;
using _RESULT_TYPE_NAME _CXX17_DEPRECATE_ADAPTOR_TYPEDEFS = size_t;

_NODISCARD _STATIC_CALL_OPERATOR size_t operator()(monostate) _CONST_CALL_OPERATOR noexcept {
return 1729; // Arbitrary value
}
};
#endif // _HAS_CXX17

#if _HAS_TR1_NAMESPACE
namespace _DEPRECATE_TR1_NAMESPACE tr1 {
using _STD get;
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36 changes: 0 additions & 36 deletions stl/inc/variant
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Expand Up @@ -1647,32 +1647,6 @@ constexpr _Ret visit(_Callable&& _Obj, _Variants&&... _Args) {
}
#endif // _HAS_CXX20

_EXPORT_STD _NODISCARD constexpr bool operator==(monostate, monostate) noexcept {
return true;
}

#if _HAS_CXX20
_EXPORT_STD _NODISCARD constexpr strong_ordering operator<=>(monostate, monostate) noexcept {
return strong_ordering::equal;
}
#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
_NODISCARD constexpr bool operator!=(monostate, monostate) noexcept {
return false;
}
_NODISCARD constexpr bool operator<(monostate, monostate) noexcept {
return false;
}
_NODISCARD constexpr bool operator>(monostate, monostate) noexcept {
return false;
}
_NODISCARD constexpr bool operator<=(monostate, monostate) noexcept {
return true;
}
_NODISCARD constexpr bool operator>=(monostate, monostate) noexcept {
return true;
}
#endif // ^^^ !_HAS_CXX20 ^^^

_EXPORT_STD template <class... _Types,
enable_if_t<conjunction_v<is_move_constructible<_Types>..., is_swappable<_Types>...>, int> = 0>
_CONSTEXPR20 void swap(variant<_Types...>& _Left, variant<_Types...>& _Right) noexcept(noexcept(_Left.swap(_Right))) {
Expand Down Expand Up @@ -1702,16 +1676,6 @@ struct hash<variant<_Types...>> : _Conditionally_enabled_hash<variant<_Types...>
}
};

template <>
struct hash<monostate> {
using _ARGUMENT_TYPE_NAME _CXX17_DEPRECATE_ADAPTOR_TYPEDEFS = monostate;
using _RESULT_TYPE_NAME _CXX17_DEPRECATE_ADAPTOR_TYPEDEFS = size_t;

_NODISCARD _STATIC_CALL_OPERATOR size_t operator()(monostate) _CONST_CALL_OPERATOR noexcept {
return 1729; // Arbitrary value
}
};

_STD_END

#undef _STL_STAMP
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4 changes: 0 additions & 4 deletions stl/inc/xutility
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Expand Up @@ -7568,10 +7568,6 @@ struct _CXX17_DEPRECATE_ITERATOR_BASE_CLASS iterator { // base type for iterator
using reference = _Reference;
};

#if _HAS_CXX17
_EXPORT_STD struct monostate {};
#endif // _HAS_CXX17

#if _HAS_CXX23
template <_Integer_like _Int>
_NODISCARD constexpr bool _Add_overflow(const _Int _Left, const _Int _Right, _Int& _Out) {
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1 change: 1 addition & 0 deletions stl/inc/yvals_core.h
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Expand Up @@ -120,6 +120,7 @@
// P0426R1 constexpr For char_traits
// P0433R2 Deduction Guides For The STL
// P0452R1 Unifying <numeric> Parallel Algorithms
// P0472R3 Put monostate In <utility>
// P0504R0 Revisiting in_place_t/in_place_type_t<T>/in_place_index_t<I>
// P0505R0 constexpr For <chrono> (Again)
// P0508R0 Clarifying insert_return_type
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