chromium/third_party/libc++/src/include/__type_traits/is_equality_comparable.h

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___TYPE_TRAITS_IS_EQUALITY_COMPARABLE_H
#define _LIBCPP___TYPE_TRAITS_IS_EQUALITY_COMPARABLE_H

#include <__config>
#include <__type_traits/enable_if.h>
#include <__type_traits/integral_constant.h>
#include <__type_traits/is_integral.h>
#include <__type_traits/is_same.h>
#include <__type_traits/is_signed.h>
#include <__type_traits/is_void.h>
#include <__type_traits/remove_cv.h>
#include <__type_traits/void_t.h>
#include <__utility/declval.h>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp, class _Up, class = void>
struct __is_equality_comparable : false_type { … };

__is_equality_comparable<_Tp, _Up, __void_t<decltype(std::declval<_Tp>() == std::declval<_Up>())>>;

// A type is_trivially_equality_comparable if the expression `a == b` is equivalent to `std::memcmp(&a, &b, sizeof(T))`
// (with `a` and `b` being of type `T`). For the case where we compare two object of the same type, we can use
// __is_trivially_equality_comparable. We have special-casing for pointers which point to the same type ignoring
// cv-qualifications and comparing to void-pointers.
//
// The following types are not trivially equality comparable:
// floating-point types: different bit-patterns can compare equal. (e.g 0.0 and -0.0)
// enums: The user is allowed to specialize operator== for enums
// pointers that don't have the same type (ignoring cv-qualifiers): pointers to virtual bases are equality comparable,
//   but don't have the same bit-pattern. An exception to this is comparing to a void-pointer. There the bit-pattern is
//   always compared.
// objects with padding bytes: since objects with padding bytes may compare equal, even though their object
//   representation may not be equivalent.

template <class _Tp, class _Up, class = void>
struct __libcpp_is_trivially_equality_comparable_impl : false_type { … };

__libcpp_is_trivially_equality_comparable_impl<_Tp, _Tp>;
#else
    : is_integral<_Tp> {
};
#endif // __has_builtin(__is_trivially_equality_comparable)

__libcpp_is_trivially_equality_comparable_impl<_Tp, _Up, __enable_if_t<is_integral<_Tp>::value && is_integral<_Up>::value && !is_same<_Tp, _Up>::value && is_signed<_Tp>::value == is_signed<_Up>::value && sizeof(_Tp) == sizeof(_Up)>>;

__libcpp_is_trivially_equality_comparable_impl<_Tp *, _Tp *>;

// TODO: Use is_pointer_inverconvertible_base_of
__libcpp_is_trivially_equality_comparable_impl<_Tp *, _Up *>;

__libcpp_is_trivially_equality_comparable;

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___TYPE_TRAITS_IS_EQUALITY_COMPARABLE_H