P2116R0 Removing tuple-Like Protocol Support From Fixed-Extent span (#587)

Fixes #556.

stl/inc/span

@@ -710,39 +710,6 @@ _NODISCARD auto as_writable_bytes(span<_Ty, _Extent> _Sp) noexcept {
 }
 #endif // __cpp_lib_byte
 
-// [span.tuple] Tuple interface
-#ifdef __cpp_lib_concepts
-
-// clang-format off
-template <class _Ty, size_t _Extent>
-    requires (_Extent != dynamic_extent)
-struct tuple_size<span<_Ty, _Extent>> : integral_constant<size_t, _Extent> {};
-// clang-format on
-
-#else // ^^^ __cpp_lib_concepts / !__cpp_lib_concepts vvv
-
-template <class _Ty, size_t _Extent>
-struct tuple_size<span<_Ty, _Extent>> : integral_constant<size_t, _Extent> {};
-
-template <class _Ty>
-struct tuple_size<span<_Ty, dynamic_extent>>;
-
-#endif // !__cpp_lib_concepts
-
-template <size_t _Index, class _Ty, size_t _Extent>
-struct _MSVC_KNOWN_SEMANTICS tuple_element<_Index, span<_Ty, _Extent>> {
-    static_assert(dynamic_extent != _Extent, "std::span<T, dynamic_extent> is not tuple-like");
-    static_assert(_Index < _Extent, "Index out of bounds for a std::span of this extent");
-    using type = _Ty;
-};
-
-template <size_t _Index, class _Ty, size_t _Extent>
-_NODISCARD constexpr _Ty& get(span<_Ty, _Extent> _Span) noexcept {
-    static_assert(dynamic_extent != _Extent, "std::get<> not supported for std::span<T, dynamic_extent>");
-    static_assert(_Index < _Extent, "Index out of bounds for a std::span of this extent");
-    return _Span[_Index];
-}
-
 _STD_END
 
 #pragma pop_macro("new")

stl/inc/yvals_core.h

@@ -199,6 +199,7 @@
 // P1976R2 Explicit Constructors For Fixed-Extent span From Dynamic-Extent Ranges
 // P2091R0 Fixing Issues With Range Access CPOs
 // P2102R0 Making "Implicit Expression Variations" More Explicit
+// P2116R0 Removing tuple-Like Protocol Support From Fixed-Extent span
 // P????R? directory_entry::clear_cache()
 
 // _HAS_CXX20 indirectly controls:

tests/libcxx/skipped_tests.txt

@@ -692,6 +692,14 @@ language.support\support.limits\support.limits.general\string.version.pass.cpp
 # Test needs to be updated for LWG-3320 removing span::const_iterator.
 containers\views\types.pass.cpp
 
+# Test needs to be updated for P2116R0 removing the tuple interface of span
+containers\views\span.tuple\get.fail.cpp
+containers\views\span.tuple\get.pass.cpp
+containers\views\span.tuple\tuple_element.fail.cpp
+containers\views\span.tuple\tuple_element.pass.cpp
+containers\views\span.tuple\tuple_size.fail.cpp
+containers\views\span.tuple\tuple_size.pass.cpp
+
 # Test bug. See LWG-3099 "is_assignable<Incomplete&, Incomplete&>"
 utilities\utility\pairs\pairs.pair\assign_pair.pass.cpp
 

tests/std/tests/P0122R7_span/test.cpp

@@ -79,15 +79,6 @@ static_assert(ranges::enable_borrowed_range<span<int>>);
 static_assert(ranges::enable_borrowed_range<span<int, 3>>);
 #endif // __cpp_lib_concepts
 
-static_assert(is_base_of_v<integral_constant<size_t, 3>, tuple_size<span<int, 3>>>);
-static_assert(is_base_of_v<integral_constant<size_t, 3>, tuple_size<const span<int, 3>>>);
-
-// LWG-3378: <span> isn't guaranteed to provide tuple_element_t; our implementation does.
-static_assert(is_same_v<tuple_element_t<2, span<int, 3>>, int>);
-static_assert(is_same_v<tuple_element_t<2, const span<int, 3>>, const int>);
-static_assert(is_same_v<tuple_element_t<2, span<const int, 3>>, const int>);
-static_assert(is_same_v<tuple_element_t<2, const span<const int, 3>>, const int>);
-
 // For performance, our implementation provides an additional guarantee beyond the Standard
 // that span and its iterator types are trivially copyable.
 static_assert(is_trivially_copyable_v<span<int>>);
@@ -1019,20 +1010,6 @@ constexpr bool test() {
         static_assert(is_same_v<decltype(sp_nine.rbegin()), span<int, 9>::reverse_iterator>);
         static_assert(is_same_v<decltype(sp_dyn.rend()), span<int>::reverse_iterator>);
         static_assert(is_same_v<decltype(sp_nine.rend()), span<int, 9>::reverse_iterator>);
-
-        static_assert(noexcept(get<5>(sp_nine)));
-        assert(get<5>(sp_nine) == 60);
-        assert(&get<5>(sp_nine) == begin(sequence) + 5);
-    }
-
-    {
-        span<int, 3> sp_three(arr);
-
-        auto& [x, y, z] = sp_three;
-
-        assert(&x == begin(arr));
-        assert(&y == begin(arr) + 1);
-        assert(&z == begin(arr) + 2);
     }
 
     return true;