requires for chrono::parse and comparison category detection (#5044)

frederick-vs-ja · CaseyCarter · web-flow · commit 30c9391b9132 · 2024-10-30T07:50:12.000-07:00
Co-authored-by: Casey Carter &lt;cartec69@gmail.com&gt;
diff --git a/stl/inc/__msvc_string_view.hpp b/stl/inc/__msvc_string_view.hpp
@@ -1756,13 +1756,14 @@ _NODISCARD constexpr bool operator==(const basic_string_view<_Elem, _Traits> _Lh
     return _Lhs._Equal(_Rhs);
 }
 
-template <class _Traits, class = void>
+template <class _Traits>
 struct _Get_comparison_category {
     using type = weak_ordering;
 };
 
 template <class _Traits>
-struct _Get_comparison_category<_Traits, void_t<typename _Traits::comparison_category>> {
+    requires requires { typename _Traits::comparison_category; }
+struct _Get_comparison_category<_Traits> {
     using type = _Traits::comparison_category;
 
     static_assert(_Is_any_of_v<type, partial_ordering, weak_ordering, strong_ordering>,
diff --git a/stl/inc/chrono b/stl/inc/chrono
@@ -4612,57 +4612,56 @@ namespace chrono {
         minutes* _Offset;
     };
 
-    template <class _CharT, class _Traits, class _Parsable, class... _Rest>
-    using _Has_from_stream =
-        decltype(static_cast<void>(from_stream(_STD declval<basic_istream<_CharT, _Traits>&>(),
-                     _STD declval<const _CharT*>(), _STD declval<_Parsable&>(), _STD declval<_Rest>()...)),
-            0); // intentional ADL
+    template <class _Parsable, class _CharT, class _Traits, class... _Rest>
+    concept _Can_from_stream = requires(
+        basic_istream<_CharT, _Traits>& __istr, const _CharT* __s, _Parsable& __parsed, _Rest&&... __rest_args) {
+        from_stream(__istr, +__s, __parsed, _STD forward<_Rest>(__rest_args)...); // intentional ADL
+    };
 
-    _EXPORT_STD template <class _CharT, class _Parsable, _Has_from_stream<_CharT, char_traits<_CharT>, _Parsable> = 0>
+    _EXPORT_STD template <class _CharT, _Can_from_stream<_CharT, char_traits<_CharT>> _Parsable>
     _NODISCARD auto parse(const _CharT* _Fmt, _Parsable& _Tp) {
         return _Time_parse_iomanip_c_str<_CharT, char_traits<_CharT>, allocator<_CharT>, _Parsable>{_Fmt, _Tp};
     }
 
-    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc, class _Parsable,
-        _Has_from_stream<_CharT, _Traits, _Parsable> = 0>
+    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc, _Can_from_stream<_CharT, _Traits> _Parsable>
     _NODISCARD auto parse(const basic_string<_CharT, _Traits, _Alloc>& _Fmt, _Parsable& _Tp) {
         return _Time_parse_iomanip{_Fmt, _Tp};
     }
 
-    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc, class _Parsable,
-        _Has_from_stream<_CharT, _Traits, _Parsable, basic_string<_CharT, _Traits, _Alloc>*> = 0>
+    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc,
+        _Can_from_stream<_CharT, _Traits, basic_string<_CharT, _Traits, _Alloc>*> _Parsable>
     _NODISCARD auto parse(const _CharT* _Fmt, _Parsable& _Tp, basic_string<_CharT, _Traits, _Alloc>& _Abbrev) {
         return _Time_parse_iomanip_c_str{_Fmt, _Tp, _STD addressof(_Abbrev)};
     }
 
-    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc, class _Parsable,
-        _Has_from_stream<_CharT, _Traits, _Parsable, basic_string<_CharT, _Traits, _Alloc>*> = 0>
+    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc,
+        _Can_from_stream<_CharT, _Traits, basic_string<_CharT, _Traits, _Alloc>*> _Parsable>
     _NODISCARD auto parse(const basic_string<_CharT, _Traits, _Alloc>& _Fmt, _Parsable& _Tp,
         basic_string<_CharT, _Traits, _Alloc>& _Abbrev) {
         return _Time_parse_iomanip{_Fmt, _Tp, _STD addressof(_Abbrev)};
     }
 
-    _EXPORT_STD template <class _CharT, class _Parsable,
-        _Has_from_stream<_CharT, char_traits<_CharT>, _Parsable, basic_string<_CharT>*, minutes*> = 0>
+    _EXPORT_STD template <class _CharT,
+        _Can_from_stream<_CharT, char_traits<_CharT>, basic_string<_CharT>*, minutes*> _Parsable>
     _NODISCARD auto parse(const _CharT* _Fmt, _Parsable& _Tp, minutes& _Offset) {
         return _Time_parse_iomanip_c_str{_Fmt, _Tp, static_cast<basic_string<_CharT>*>(nullptr), &_Offset};
     }
 
-    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc, class _Parsable,
-        _Has_from_stream<_CharT, _Traits, _Parsable, basic_string<_CharT, _Traits, _Alloc>*, minutes*> = 0>
+    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc,
+        _Can_from_stream<_CharT, _Traits, basic_string<_CharT, _Traits, _Alloc>*, minutes*> _Parsable>
     _NODISCARD auto parse(const basic_string<_CharT, _Traits, _Alloc>& _Fmt, _Parsable& _Tp, minutes& _Offset) {
         return _Time_parse_iomanip{_Fmt, _Tp, static_cast<basic_string<_CharT, _Traits, _Alloc>*>(nullptr), &_Offset};
     }
 
-    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc, class _Parsable,
-        _Has_from_stream<_CharT, _Traits, _Parsable, basic_string<_CharT, _Traits, _Alloc>*, minutes*> = 0>
+    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc,
+        _Can_from_stream<_CharT, _Traits, basic_string<_CharT, _Traits, _Alloc>*, minutes*> _Parsable>
     _NODISCARD auto parse(
         const _CharT* _Fmt, _Parsable& _Tp, basic_string<_CharT, _Traits, _Alloc>& _Abbrev, minutes& _Offset) {
         return _Time_parse_iomanip_c_str{_Fmt, _Tp, _STD addressof(_Abbrev), &_Offset};
     }
 
-    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc, class _Parsable,
-        _Has_from_stream<_CharT, _Traits, _Parsable, basic_string<_CharT, _Traits, _Alloc>*, minutes*> = 0>
+    _EXPORT_STD template <class _CharT, class _Traits, class _Alloc,
+        _Can_from_stream<_CharT, _Traits, basic_string<_CharT, _Traits, _Alloc>*, minutes*> _Parsable>
     _NODISCARD auto parse(const basic_string<_CharT, _Traits, _Alloc>& _Fmt, _Parsable& _Tp,
         basic_string<_CharT, _Traits, _Alloc>& _Abbrev, minutes& _Offset) {
         return _Time_parse_iomanip{_Fmt, _Tp, _STD addressof(_Abbrev), &_Offset};
diff --git a/stl/inc/regex b/stl/inc/regex
@@ -605,18 +605,6 @@ bool _Is_word(_Elem _Ch) {
     return _UCh <= static_cast<_UElem>('z') && _Is_word(static_cast<unsigned char>(_UCh));
 }
 
-#if _HAS_CXX20
-template <class _Ty, class = void>
-struct _Get_member_comparison_category {
-    using type = weak_ordering;
-};
-
-template <class _Ty>
-struct _Get_member_comparison_category<_Ty, void_t<typename _Ty::comparison_category>> {
-    using type = _Ty::comparison_category;
-};
-#endif // _HAS_CXX20
-
 _EXPORT_STD template <class _BidIt>
 class sub_match : public pair<_BidIt, _BidIt> { // class to hold contents of a capture group
 public:
@@ -630,10 +618,6 @@ public:
     // Note that _Size_type should always be std::size_t
     using _Size_type = typename string_type::size_type;
 
-#if _HAS_CXX20
-    using _Comparison_category = _Get_member_comparison_category<_Traits>::type;
-#endif // _HAS_CXX20
-
     constexpr sub_match() : _Mybase(), matched(false) {}
 
     bool matched;
@@ -744,7 +728,8 @@ _NODISCARD bool operator==(const sub_match<_BidIt>& _Left, const sub_match<_BidI
 #if _HAS_CXX20
 _EXPORT_STD template <class _BidIt>
 _NODISCARD auto operator<=>(const sub_match<_BidIt>& _Left, const sub_match<_BidIt>& _Right) {
-    return static_cast<sub_match<_BidIt>::_Comparison_category>(_Left.compare(_Right) <=> 0);
+    using _Comparison_category = _Get_comparison_category_t<char_traits<_Iter_value_t<_BidIt>>>;
+    return static_cast<_Comparison_category>(_Left.compare(_Right) <=> 0);
 }
 #else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
 template <class _BidIt>
@@ -781,7 +766,8 @@ _NODISCARD bool operator==(const sub_match<_BidIt>& _Left, const _Iter_value_t<_
 #if _HAS_CXX20
 _EXPORT_STD template <class _BidIt>
 _NODISCARD auto operator<=>(const sub_match<_BidIt>& _Left, const _Iter_value_t<_BidIt>* _Right) {
-    return static_cast<sub_match<_BidIt>::_Comparison_category>(_Left.compare(_Right) <=> 0);
+    using _Comparison_category = _Get_comparison_category_t<char_traits<_Iter_value_t<_BidIt>>>;
+    return static_cast<_Comparison_category>(_Left.compare(_Right) <=> 0);
 }
 #else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
 template <class _BidIt>
@@ -848,7 +834,8 @@ _NODISCARD bool operator==(const sub_match<_BidIt>& _Left, const _Iter_value_t<_
 #if _HAS_CXX20
 _EXPORT_STD template <class _BidIt>
 _NODISCARD auto operator<=>(const sub_match<_BidIt>& _Left, const _Iter_value_t<_BidIt>& _Right) {
-    return static_cast<sub_match<_BidIt>::_Comparison_category>(_Left._Compare(_STD addressof(_Right), 1) <=> 0);
+    using _Comparison_category = _Get_comparison_category_t<char_traits<_Iter_value_t<_BidIt>>>;
+    return static_cast<_Comparison_category>(_Left._Compare(_STD addressof(_Right), 1) <=> 0);
 }
 #else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
 template <class _BidIt>
@@ -917,7 +904,8 @@ _NODISCARD bool operator==(
 _EXPORT_STD template <class _BidIt, class _Traits, class _Alloc>
 _NODISCARD auto operator<=>(
     const sub_match<_BidIt>& _Left, const basic_string<_Iter_value_t<_BidIt>, _Traits, _Alloc>& _Right) {
-    return static_cast<sub_match<_BidIt>::_Comparison_category>(_Left._Compare(_Right.data(), _Right.size()) <=> 0);
+    using _Comparison_category = _Get_comparison_category_t<char_traits<_Iter_value_t<_BidIt>>>;
+    return static_cast<_Comparison_category>(_Left._Compare(_Right.data(), _Right.size()) <=> 0);
 }
 #else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
 template <class _BidIt, class _Traits, class _Alloc>
