From ecbc1efa09936f4ef5af529e770a95a29a4290d3 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Fri, 12 Jul 2024 06:25:56 +0800
Subject: [PATCH] Use `requires`-clauses for `pair` and `tuple` since C++20 
 (#4819)

---
 stl/inc/expected | 12 ++----------
 stl/inc/tuple    | 38 ++++++++++++++++++--------------------
 stl/inc/utility  | 41 ++++++++++++++++++-----------------------
 3 files changed, 38 insertions(+), 53 deletions(-)

diff --git a/stl/inc/expected b/stl/inc/expected
index 28e74e7118..aad81b7007 100644
--- a/stl/inc/expected
+++ b/stl/inc/expected
@@ -87,11 +87,7 @@ public:
     }
 
     friend constexpr void swap(unexpected& _Left, unexpected& _Right) noexcept(is_nothrow_swappable_v<_Err>)
-#if defined(__clang__) || defined(__EDG__) // TRANSITION, /permissive
-        requires is_swappable_v<_Err>
-#else // ^^^ no workaround / workaround vvv
-        requires is_swappable<_Err>::value
-#endif // ^^^ workaround ^^^
+        requires is_swappable<_Err>::value // TRANSITION, /permissive needs ::value
     {
         _Left.swap(_Right);
     }
@@ -612,11 +608,7 @@ public:
     friend constexpr void swap(expected& _Lhs, expected& _Rhs) noexcept(
         is_nothrow_move_constructible_v<_Ty> && is_nothrow_swappable_v<_Ty> && is_nothrow_move_constructible_v<_Err>
         && is_nothrow_swappable_v<_Err>)
-#if defined(__clang__) || defined(__EDG__) // TRANSITION, /permissive
-        requires is_swappable_v<_Ty> && is_swappable_v<_Err>
-#else // ^^^ no workaround / workaround vvv
-        requires is_swappable<_Ty>::value && is_swappable<_Err>::value
-#endif // ^^^ workaround ^^^
+        requires is_swappable<_Ty>::value && is_swappable<_Err>::value // TRANSITION, /permissive needs ::value
               && is_move_constructible_v<_Ty> && is_move_constructible_v<_Err>
               && (is_nothrow_move_constructible_v<_Ty> || is_nothrow_move_constructible_v<_Err>)
     {
diff --git a/stl/inc/tuple b/stl/inc/tuple
index 79315abf56..0f79be7872 100644
--- a/stl/inc/tuple
+++ b/stl/inc/tuple
@@ -553,12 +553,11 @@ public:
     }
 
 #if _HAS_CXX23
-    template <class _Myself = tuple, class _This2 = _This,
-        enable_if_t<conjunction_v<_STD _Is_copy_assignable_no_precondition_check<const _This2>,
-                        _STD _Is_copy_assignable_no_precondition_check<const _Rest>...>,
-            int> = 0>
+    template <class _Myself = tuple>
+        requires conjunction_v<_STD _Is_copy_assignable_no_precondition_check<const _This>,
+            _STD _Is_copy_assignable_no_precondition_check<const _Rest>...>
     constexpr const tuple& operator=(_Identity_t<const _Myself&> _Right) const
-        noexcept(conjunction_v<is_nothrow_copy_assignable<const _This2>,
+        noexcept(conjunction_v<is_nothrow_copy_assignable<const _This>,
             is_nothrow_copy_assignable<const _Rest>...>) /* strengthened */ {
         _Myfirst._Val = _Right._Myfirst._Val;
         _Get_rest()   = _Right._Get_rest();
@@ -578,12 +577,11 @@ public:
     }
 
 #if _HAS_CXX23
-    template <class _Myself = tuple, class _This2 = _This,
-        enable_if_t<conjunction_v<_STD _Is_assignable_no_precondition_check<const _This2&, _This2>,
-                        _STD _Is_assignable_no_precondition_check<const _Rest&, _Rest>...>,
-            int> = 0>
+    template <class _Myself = tuple>
+        requires conjunction_v<_STD _Is_assignable_no_precondition_check<const _This&, _This>,
+            _STD _Is_assignable_no_precondition_check<const _Rest&, _Rest>...>
     constexpr const tuple& operator=(_Identity_t<_Myself&&> _Right) const
-        noexcept(conjunction_v<is_nothrow_assignable<const _This2&, _This2>,
+        noexcept(conjunction_v<is_nothrow_assignable<const _This&, _This>,
             is_nothrow_assignable<const _Rest&, _Rest>...>) /* strengthened */ {
         _Myfirst._Val = _STD forward<_This>(_Right._Myfirst._Val);
         _Get_rest()   = _STD forward<_Mybase>(_Right._Get_rest());
@@ -602,9 +600,8 @@ public:
     }
 
 #if _HAS_CXX23
-    template <class... _Other, enable_if_t<conjunction_v<_STD negation<_STD is_same<tuple, _STD tuple<_Other...>>>,
-                                               _STD _Tuple_assignable_val<const tuple, const _Other&...>>,
-                                   int> = 0>
+    template <class... _Other>
+        requires (!is_same_v<tuple, _STD tuple<_Other...>>) && _Tuple_assignable_v<const tuple, const _Other&...>
     constexpr const tuple& operator=(const tuple<_Other...>& _Right) const
         noexcept(_Tuple_nothrow_assignable_v<const tuple, const _Other&...>) /* strengthened */ {
         _Myfirst._Val = _Right._Myfirst._Val;
@@ -624,9 +621,8 @@ public:
     }
 
 #if _HAS_CXX23
-    template <class... _Other, enable_if_t<conjunction_v<_STD negation<_STD is_same<tuple, _STD tuple<_Other...>>>,
-                                               _STD _Tuple_assignable_val<const tuple, _Other...>>,
-                                   int> = 0>
+    template <class... _Other>
+        requires (!is_same_v<tuple, _STD tuple<_Other...>>) && _Tuple_assignable_v<const tuple, _Other...>
     constexpr const tuple& operator=(tuple<_Other...>&& _Right) const
         noexcept(_Tuple_nothrow_assignable_v<const tuple, _Other...>) /* strengthened */ {
         _Myfirst._Val = _STD forward<typename tuple<_Other...>::_This_type>(_Right._Myfirst._Val);
@@ -645,8 +641,8 @@ public:
     }
 
 #if _HAS_CXX23
-    template <class _First, class _Second,
-        enable_if_t<_Tuple_assignable_v<const tuple, const _First&, const _Second&>, int> = 0>
+    template <class _First, class _Second>
+        requires _Tuple_assignable_v<const tuple, const _First&, const _Second&>
     constexpr const tuple& operator=(const pair<_First, _Second>& _Right) const
         noexcept(_Tuple_nothrow_assignable_v<const tuple, const _First&, const _Second&>) /* strengthened */ {
         _Myfirst._Val             = _Right.first;
@@ -664,7 +660,8 @@ public:
     }
 
 #if _HAS_CXX23
-    template <class _First, class _Second, enable_if_t<_Tuple_assignable_v<const tuple, _First, _Second>, int> = 0>
+    template <class _First, class _Second>
+        requires _Tuple_assignable_v<const tuple, _First, _Second>
     constexpr const tuple& operator=(pair<_First, _Second>&& _Right) const
         noexcept(_Tuple_nothrow_assignable_v<const tuple, _First, _Second>) /* strengthened */ {
         _Myfirst._Val             = _STD forward<_First>(_Right.first);
@@ -896,7 +893,8 @@ _CONSTEXPR20 void swap(tuple<_Types...>& _Left, tuple<_Types...>& _Right) noexce
 }
 
 #if _HAS_CXX23
-_EXPORT_STD template <class... _Types, enable_if_t<conjunction_v<is_swappable<const _Types>...>, int> = 0>
+_EXPORT_STD template <class... _Types>
+    requires conjunction_v<is_swappable<const _Types>...>
 constexpr void swap(const tuple<_Types...>& _Left, const tuple<_Types...>& _Right) noexcept(
     noexcept(_Left.swap(_Right))) {
     _Left.swap(_Right);
diff --git a/stl/inc/utility b/stl/inc/utility
index 0a5ea0e810..df825320fd 100644
--- a/stl/inc/utility
+++ b/stl/inc/utility
@@ -261,8 +261,8 @@ struct pair { // store a pair of values
     pair(pair&&)      = default;
 
 #if _HAS_CXX23
-    template <class _Other1, class _Other2,
-        enable_if_t<conjunction_v<is_constructible<_Ty1, _Other1&>, is_constructible<_Ty2, _Other2&>>, int> = 0>
+    template <class _Other1, class _Other2>
+        requires is_constructible_v<_Ty1, _Other1&> && is_constructible_v<_Ty2, _Other2&>
     constexpr explicit(!conjunction_v<is_convertible<_Other1&, _Ty1>, is_convertible<_Other2&, _Ty2>>)
         pair(pair<_Other1, _Other2>& _Right) noexcept(
             is_nothrow_constructible_v<_Ty1, _Other1&> && is_nothrow_constructible_v<_Ty2, _Other2&>) // strengthened
@@ -286,9 +286,8 @@ struct pair { // store a pair of values
         : first(_STD forward<_Other1>(_Right.first)), second(_STD forward<_Other2>(_Right.second)) {}
 
 #if _HAS_CXX23
-    template <class _Other1, class _Other2,
-        enable_if_t<conjunction_v<is_constructible<_Ty1, const _Other1>, is_constructible<_Ty2, const _Other2>>, int> =
-            0>
+    template <class _Other1, class _Other2>
+        requires is_constructible_v<_Ty1, const _Other1> && is_constructible_v<_Ty2, const _Other2>
     constexpr explicit(!conjunction_v<is_convertible<const _Other1, _Ty1>, is_convertible<const _Other2, _Ty2>>)
         pair(const pair<_Other1, _Other2>&& _Right) noexcept(
             is_nothrow_constructible_v<_Ty1, const _Other1>
@@ -335,10 +334,9 @@ struct pair { // store a pair of values
     }
 
 #if _HAS_CXX23
-    template <class _Myself = pair,
-        enable_if_t<conjunction_v<_Is_copy_assignable_no_precondition_check<const typename _Myself::first_type>,
-                        _Is_copy_assignable_no_precondition_check<const typename _Myself::second_type>>,
-            int>            = 0>
+    template <class _Myself = pair>
+        requires _Is_copy_assignable_unchecked_v<const typename _Myself::first_type>
+              && _Is_copy_assignable_unchecked_v<const typename _Myself::second_type>
     constexpr const pair& operator=(_Identity_t<const _Myself&> _Right) const
         noexcept(conjunction_v<is_nothrow_copy_assignable<const _Ty1>,
             is_nothrow_copy_assignable<const _Ty2>>) /* strengthened */ {
@@ -360,10 +358,9 @@ struct pair { // store a pair of values
     }
 
 #if _HAS_CXX23
-    template <class _Myself = pair,
-        enable_if_t<conjunction_v<_Is_assignable_no_precondition_check<const typename _Myself::first_type&, _Ty1>,
-                        _Is_assignable_no_precondition_check<const typename _Myself::second_type&, _Ty2>>,
-            int>            = 0>
+    template <class _Myself = pair>
+        requires _Is_assignable_no_precondition_check<const typename _Myself::first_type&, _Ty1>::value
+              && _Is_assignable_no_precondition_check<const typename _Myself::second_type&, _Ty2>::value
     constexpr const pair& operator=(_Identity_t<_Myself&&> _Right) const
         noexcept(conjunction_v<is_nothrow_assignable<const _Ty1&, _Ty1>,
             is_nothrow_assignable<const _Ty2&, _Ty2>>) /* strengthened */ {
@@ -386,10 +383,9 @@ struct pair { // store a pair of values
     }
 
 #if _HAS_CXX23
-    template <class _Other1, class _Other2,
-        enable_if_t<conjunction_v<negation<is_same<pair, pair<_Other1, _Other2>>>,
-                        is_assignable<const _Ty1&, const _Other1&>, is_assignable<const _Ty2&, const _Other2&>>,
-            int> = 0>
+    template <class _Other1, class _Other2>
+        requires (!is_same_v<pair, pair<_Other1, _Other2>>)
+              && is_assignable_v<const _Ty1&, const _Other1&> && is_assignable_v<const _Ty2&, const _Other2&>
     constexpr const pair& operator=(const pair<_Other1, _Other2>& _Right) const
         noexcept(is_nothrow_assignable_v<const _Ty1&, const _Other1&>
                  && is_nothrow_assignable_v<const _Ty2&, const _Other2&>) /* strengthened */ {
@@ -411,10 +407,9 @@ struct pair { // store a pair of values
     }
 
 #if _HAS_CXX23
-    template <class _Other1, class _Other2,
-        enable_if_t<conjunction_v<negation<is_same<pair, pair<_Other1, _Other2>>>, is_assignable<const _Ty1&, _Other1>,
-                        is_assignable<const _Ty2&, _Other2>>,
-            int> = 0>
+    template <class _Other1, class _Other2>
+        requires (!is_same_v<pair, pair<_Other1, _Other2>>)
+              && is_assignable_v<const _Ty1&, _Other1> && is_assignable_v<const _Ty2&, _Other2>
     constexpr const pair& operator=(pair<_Other1, _Other2>&& _Right) const
         noexcept(is_nothrow_assignable_v<const _Ty1&, _Other1>
                  && is_nothrow_assignable_v<const _Ty2&, _Other2>) /* strengthened */ {
@@ -481,8 +476,8 @@ _CONSTEXPR20 void swap(pair<_Ty1, _Ty2>& _Left, pair<_Ty1, _Ty2>& _Right) noexce
 }
 
 #if _HAS_CXX23
-_EXPORT_STD template <class _Ty1, class _Ty2,
-    enable_if_t<is_swappable_v<const _Ty1> && is_swappable_v<const _Ty2>, int> = 0>
+_EXPORT_STD template <class _Ty1, class _Ty2>
+    requires is_swappable<const _Ty1>::value && is_swappable<const _Ty2>::value // TRANSITION, /permissive needs ::value
 constexpr void swap(const pair<_Ty1, _Ty2>& _Left, const pair<_Ty1, _Ty2>& _Right) noexcept(
     noexcept(_Left.swap(_Right))) {
     _Left.swap(_Right);