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_SYNTH_THREE_WAY_H
10 #define _LIBCPP___COMPARE_SYNTH_THREE_WAY_H
11 
12 #include <__compare/ordering.h>
13 #include <__compare/three_way_comparable.h>
14 #include <__concepts/boolean_testable.h>
15 #include <__config>
16 #include <__utility/declval.h>
17 
18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19 #  pragma GCC system_header
20 #endif
21 
22 _LIBCPP_BEGIN_NAMESPACE_STD
23 
24 #if _LIBCPP_STD_VER >= 20
25 
26 // [expos.only.func]
27 
28 // TODO MODULES restore the lamba to match the Standard.
29 // See https://github.com/llvm/llvm-project/issues/57222
30 //_LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way =
31 //  []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
32 template <class _Tp, class _Up>
33 _LIBCPP_HIDE_FROM_ABI constexpr auto __synth_three_way(const _Tp& __t, const _Up& __u)
34   requires requires {
35     { __t < __u } -> __boolean_testable;
36     { __u < __t } -> __boolean_testable;
37   }
38 {
39   if constexpr (three_way_comparable_with<_Tp, _Up>) {
40     return __t <=> __u;
41   } else {
42     if (__t < __u)
43       return weak_ordering::less;
44     if (__u < __t)
45       return weak_ordering::greater;
46     return weak_ordering::equivalent;
47   }
48 }
49 
50 template <class _Tp, class _Up = _Tp>
51 using __synth_three_way_result = decltype(std::__synth_three_way(std::declval<_Tp&>(), std::declval<_Up&>()));
52 
53 #endif // _LIBCPP_STD_VER >= 20
54 
55 _LIBCPP_END_NAMESPACE_STD
56 
57 #endif // _LIBCPP___COMPARE_SYNTH_THREE_WAY_H
58