1 //===----------------------------------------------------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #ifndef _LIBCPP___TYPE_TRAITS_IS_EQUALITY_COMPARABLE_H 10 #define _LIBCPP___TYPE_TRAITS_IS_EQUALITY_COMPARABLE_H 11 12 #include <__config> 13 #include <__type_traits/integral_constant.h> 14 #include <__type_traits/is_integral.h> 15 #include <__type_traits/is_same.h> 16 #include <__type_traits/is_void.h> 17 #include <__type_traits/remove_cv.h> 18 #include <__type_traits/remove_cvref.h> 19 #include <__type_traits/void_t.h> 20 #include <__utility/declval.h> 21 22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 23 # pragma GCC system_header 24 #endif 25 26 _LIBCPP_BEGIN_NAMESPACE_STD 27 28 template <class _Tp, class _Up, class = void> 29 struct __is_equality_comparable : false_type {}; 30 31 template <class _Tp, class _Up> 32 struct __is_equality_comparable<_Tp, _Up, __void_t<decltype(std::declval<_Tp>() == std::declval<_Up>())> > : true_type { 33 }; 34 35 // A type is_trivially_equality_comparable if the expression `a == b` is equivalent to `std::memcmp(&a, &b, sizeof(T))` 36 // (with `a` and `b` being of type `T`). For the case where we compare two object of the same type, we can use 37 // __is_trivially_equality_comparable. We have special-casing for pointers which point to the same type ignoring 38 // cv-qualifications and comparing to void-pointers. 39 // 40 // The following types are not trivially equality comparable: 41 // floating-point types: different bit-patterns can compare equal. (e.g 0.0 and -0.0) 42 // enums: The user is allowed to specialize operator== for enums 43 // pointers that don't have the same type (ignoring cv-qualifiers): pointers to virtual bases are equality comparable, 44 // but don't have the same bit-pattern. An exception to this is comparing to a void-pointer. There the bit-pattern is 45 // always compared. 46 47 template <class _Tp, class _Up> 48 struct __libcpp_is_trivially_equality_comparable_impl : false_type {}; 49 50 template <class _Tp> 51 struct __libcpp_is_trivially_equality_comparable_impl<_Tp, _Tp> 52 #if __has_builtin(__is_trivially_equality_comparable) 53 : integral_constant<bool, __is_trivially_equality_comparable(_Tp) && __is_equality_comparable<_Tp, _Tp>::value> { 54 }; 55 #else 56 : is_integral<_Tp> { 57 }; 58 #endif // __has_builtin(__is_trivially_equality_comparable) 59 60 template <class _Tp> 61 struct __libcpp_is_trivially_equality_comparable_impl<_Tp*, _Tp*> : true_type {}; 62 63 // TODO: Use is_pointer_inverconvertible_base_of 64 template <class _Tp, class _Up> 65 struct __libcpp_is_trivially_equality_comparable_impl<_Tp*, _Up*> 66 : integral_constant< 67 bool, 68 __is_equality_comparable<_Tp*, _Up*>::value && 69 (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value || is_void<_Tp>::value || is_void<_Up>::value)> { 70 }; 71 72 template <class _Tp, class _Up> 73 using __libcpp_is_trivially_equality_comparable = 74 __libcpp_is_trivially_equality_comparable_impl<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >; 75 76 _LIBCPP_END_NAMESPACE_STD 77 78 #endif // _LIBCPP___TYPE_TRAITS_IS_EQUALITY_COMPARABLE_H 79