From: Jonathan Wakely Date: Fri, 23 Sep 2022 22:16:30 +0000 (+0100) Subject: libstdc++: Simplify detection idiom using concepts X-Git-Tag: basepoints/gcc-14~4377 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2b667beba693e876322af7c6682f9bc885c5ec28;p=thirdparty%2Fgcc.git libstdc++: Simplify detection idiom using concepts Add a simpler definition of std::__detected_or using concepts. This also replaces the __detector::value_t member which should have been using a reserved name. Use __detected_or in pointer_traits. libstdc++-v3/ChangeLog: * include/bits/alloc_traits.h (allocator_traits::is_always_equal): Only instantiate is_empty if needed. * include/bits/ptr_traits.h (__ptr_traits_impl::difference_type) (__ptr_traits_impl::rebind): Use __detected_or. * include/experimental/type_traits (is_same_v): Add a partial specialization instead of instantiating the std::is_same class template. (detected_t): Redefine in terms of detected_or_t. (is_detected, is_detected_v): Redefine in terms of detected_t. * include/std/type_traits [__cpp_concepts] (__detected_or): Add new definition using concepts. (__detector::value_t): Rename to __is_detected. * testsuite/17_intro/names.cc: Check value_t isn't used. --- diff --git a/libstdc++-v3/include/bits/alloc_traits.h b/libstdc++-v3/include/bits/alloc_traits.h index 507e8f1b6b2d..8479bfd612f6 100644 --- a/libstdc++-v3/include/bits/alloc_traits.h +++ b/libstdc++-v3/include/bits/alloc_traits.h @@ -74,7 +74,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template using __pocs = typename _Tp::propagate_on_container_swap; template - using __equal = typename _Tp::is_always_equal; + using __equal = __type_identity; }; template @@ -209,7 +209,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION * otherwise @c is_empty::type */ using is_always_equal - = __detected_or_t::type, __equal, _Alloc>; + = typename __detected_or_t, __equal, _Alloc>::type; template using rebind_alloc = __alloc_rebind<_Alloc, _Tp>; diff --git a/libstdc++-v3/include/bits/ptr_traits.h b/libstdc++-v3/include/bits/ptr_traits.h index 8360c3b6557d..ae8810706abf 100644 --- a/libstdc++-v3/include/bits/ptr_traits.h +++ b/libstdc++-v3/include/bits/ptr_traits.h @@ -144,29 +144,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION struct __ptr_traits_impl : __ptr_traits_ptr_to<_Ptr, _Elt> { private: - template - struct __difference { using type = ptrdiff_t; }; - template -#if __cpp_concepts - requires requires { typename _Tp::difference_type; } - struct __difference<_Tp> -#else - struct __difference<_Tp, __void_t> -#endif - { using type = typename _Tp::difference_type; }; - - template - struct __rebind : __replace_first_arg<_Tp, _Up> { }; + using __diff_t = typename _Tp::difference_type; template -#if __cpp_concepts - requires requires { typename _Tp::template rebind<_Up>; } - struct __rebind<_Tp, _Up> -#else - struct __rebind<_Tp, _Up, __void_t>> -#endif - { using type = typename _Tp::template rebind<_Up>; }; + using __rebind = __type_identity>; public: /// The pointer type. @@ -176,11 +158,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION using element_type = _Elt; /// The type used to represent the difference between two pointers. - using difference_type = typename __difference<_Ptr>::type; + using difference_type = __detected_or_t; /// A pointer to a different type. template - using rebind = typename __rebind<_Ptr, _Up>::type; + using rebind = typename __detected_or_t<__replace_first_arg<_Ptr, _Up>, + __rebind, _Ptr, _Up>::type; }; // _GLIBCXX_RESOLVE_LIB_DEFECTS diff --git a/libstdc++-v3/include/experimental/type_traits b/libstdc++-v3/include/experimental/type_traits index af5970e80d02..fa25a1c2be26 100644 --- a/libstdc++-v3/include/experimental/type_traits +++ b/libstdc++-v3/include/experimental/type_traits @@ -223,7 +223,9 @@ template // See C++14 20.10.6, type relations template - constexpr bool is_same_v = is_same<_Tp, _Up>::value; + constexpr bool is_same_v = false; +template + constexpr bool is_same_v<_Tp, _Tp> = true; template constexpr bool is_base_of_v = is_base_of<_Base, _Derived>::value; template @@ -266,23 +268,21 @@ struct nonesuch : private __nonesuchbase }; #pragma GCC diagnostic pop -template class _Op, typename... _Args> - using is_detected - = typename std::__detector::value_t; - -template class _Op, typename... _Args> - constexpr bool is_detected_v = is_detected<_Op, _Args...>::value; - -template class _Op, typename... _Args> - using detected_t - = typename std::__detector::type; - template class _Op, typename... _Args> using detected_or = std::__detected_or<_Default, _Op, _Args...>; template class _Op, typename... _Args> using detected_or_t = typename detected_or<_Default, _Op, _Args...>::type; +template class _Op, typename... _Args> + using detected_t = detected_or_t; + +template class _Op, typename... _Args> + using is_detected = typename detected_or::__is_detected; + +template class _Op, typename... _Args> + constexpr bool is_detected_v = is_detected<_Op, _Args...>::value; + template class _Op, typename... _Args> using is_detected_exact = is_same<_Expected, detected_t<_Op, _Args...>>; diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits index 7c635313a956..c5853fcad906 100644 --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -2551,13 +2551,34 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION /// @cond undocumented + // Detection idiom. + // Detect whether _Op<_Args...> is a valid type, use default _Def if not. + +#if __cpp_concepts + // Implementation of the detection idiom (negative case). + template class _Op, typename... _Args> + struct __detected_or + { + using type = _Def; + using __is_detected = false_type; + }; + + // Implementation of the detection idiom (positive case). + template class _Op, typename... _Args> + requires requires { typename _Op<_Args...>; } + struct __detected_or<_Def, _Op, _Args...> + { + using type = _Op<_Args...>; + using __is_detected = true_type; + }; +#else /// Implementation of the detection idiom (negative case). template class _Op, typename... _Args> struct __detector { - using value_t = false_type; using type = _Default; + using __is_detected = false_type; }; /// Implementation of the detection idiom (positive case). @@ -2565,14 +2586,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION typename... _Args> struct __detector<_Default, __void_t<_Op<_Args...>>, _Op, _Args...> { - using value_t = true_type; using type = _Op<_Args...>; + using __is_detected = true_type; }; - // Detect whether _Op<_Args...> is a valid type, use _Default if not. template class _Op, typename... _Args> using __detected_or = __detector<_Default, void, _Op, _Args...>; +#endif // __cpp_concepts // _Op<_Args...> if that is a valid type, otherwise _Default. template class _Op, diff --git a/libstdc++-v3/testsuite/17_intro/names.cc b/libstdc++-v3/testsuite/17_intro/names.cc index 82e201c71b0c..6490cd633071 100644 --- a/libstdc++-v3/testsuite/17_intro/names.cc +++ b/libstdc++-v3/testsuite/17_intro/names.cc @@ -112,6 +112,7 @@ #define tmp ( #define sz ( #define token ( +#define value_t ( #if __cplusplus < 201103L #define uses_allocator (