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___COMPARE_COMPARE_THREE_WAY_RESULT_H
10 #define _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H
11 
12 #include <__config>
13 #include <__type_traits/make_const_lvalue_ref.h>
14 #include <__utility/declval.h>
15 
16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17 #  pragma GCC system_header
18 #endif
19 
20 _LIBCPP_BEGIN_NAMESPACE_STD
21 
22 #if _LIBCPP_STD_VER > 17
23 
24 template<class, class, class>
25 struct _LIBCPP_HIDE_FROM_ABI __compare_three_way_result { };
26 
27 template<class _Tp, class _Up>
28 struct _LIBCPP_HIDE_FROM_ABI __compare_three_way_result<_Tp, _Up, decltype(
29   std::declval<__make_const_lvalue_ref<_Tp>>() <=> std::declval<__make_const_lvalue_ref<_Up>>(), void()
30 )> {
31     using type = decltype(std::declval<__make_const_lvalue_ref<_Tp>>() <=> std::declval<__make_const_lvalue_ref<_Up>>());
32 };
33 
34 template<class _Tp, class _Up = _Tp>
35 struct _LIBCPP_TEMPLATE_VIS compare_three_way_result : __compare_three_way_result<_Tp, _Up, void> { };
36 
37 template<class _Tp, class _Up = _Tp>
38 using compare_three_way_result_t = typename compare_three_way_result<_Tp, _Up>::type;
39 
40 #endif // _LIBCPP_STD_VER > 17
41 
42 _LIBCPP_END_NAMESPACE_STD
43 
44 #endif // _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H
45