From 4d6c0e864425d119df02edce8cb9749cca080a75 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Yehuda=20Bern=C3=A1th?= <yehudamber@gmail.com>
Date: Mon, 31 Mar 2025 19:29:55 +0300
Subject: [PATCH 1/3] Implement P0472R3 - Move monostate to <utility>

---
 stl/inc/utility  | 30 ++++++++++++++++++++++++++++++
 stl/inc/variant  | 26 --------------------------
 stl/inc/xutility |  4 ----
 3 files changed, 30 insertions(+), 30 deletions(-)

diff --git a/stl/inc/utility b/stl/inc/utility
index 999de93c950..01260e6d905 100644
--- a/stl/inc/utility
+++ b/stl/inc/utility
@@ -973,6 +973,36 @@ _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 ^^^
+#endif // _HAS_CXX17
+
 #if _HAS_TR1_NAMESPACE
 namespace _DEPRECATE_TR1_NAMESPACE tr1 {
     using _STD get;
diff --git a/stl/inc/variant b/stl/inc/variant
index e2a2e7581c6..5006458bbc2 100644
--- a/stl/inc/variant
+++ b/stl/inc/variant
@@ -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))) {
diff --git a/stl/inc/xutility b/stl/inc/xutility
index fbce0c9df7c..d93f3b606d5 100644
--- a/stl/inc/xutility
+++ b/stl/inc/xutility
@@ -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) {

From 0463c5b61b874cd164399d8bc7ff4bbdeb26e66d Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Mon, 31 Mar 2025 14:15:39 -0700
Subject: [PATCH 2/3] Add P0472R3 to the C++17 section of yvals_core.h.

---
 stl/inc/yvals_core.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/stl/inc/yvals_core.h b/stl/inc/yvals_core.h
index 2e1f7472d11..fcbb50a4692 100644
--- a/stl/inc/yvals_core.h
+++ b/stl/inc/yvals_core.h
@@ -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

From c68bd230125160ad65db0e93b709e64ed2483733 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Yehuda=20Bern=C3=A1th?= <yehudamber@gmail.com>
Date: Tue, 1 Apr 2025 14:29:11 +0300
Subject: [PATCH 3/3] Move hash<monostate> to <utility>

---
 stl/inc/utility | 10 ++++++++++
 stl/inc/variant | 10 ----------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/stl/inc/utility b/stl/inc/utility
index 01260e6d905..4570a7bb790 100644
--- a/stl/inc/utility
+++ b/stl/inc/utility
@@ -1001,6 +1001,16 @@ _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
diff --git a/stl/inc/variant b/stl/inc/variant
index 5006458bbc2..c17d88fe17e 100644
--- a/stl/inc/variant
+++ b/stl/inc/variant
@@ -1676,16 +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