1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___VARIANT_MONOSTATE_H 11 #define _LIBCPP___VARIANT_MONOSTATE_H 12 13 #include <__compare/ordering.h> 14 #include <__config> 15 #include <__functional/hash.h> 16 #include <cstddef> 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 >= 17 25 26 struct _LIBCPP_TEMPLATE_VIS monostate {}; 27 28 _LIBCPP_HIDE_FROM_ABI constexpr bool operator==(monostate, monostate) noexcept { return true; } 29 30 # if _LIBCPP_STD_VER >= 20 31 32 _LIBCPP_HIDE_FROM_ABI constexpr strong_ordering operator<=>(monostate, monostate) noexcept { 33 return strong_ordering::equal; 34 } 35 36 # else // _LIBCPP_STD_VER >= 20 37 38 _LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(monostate, monostate) noexcept { return false; } 39 40 _LIBCPP_HIDE_FROM_ABI constexpr bool operator<(monostate, monostate) noexcept { return false; } 41 42 _LIBCPP_HIDE_FROM_ABI constexpr bool operator>(monostate, monostate) noexcept { return false; } 43 44 _LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(monostate, monostate) noexcept { return true; } 45 46 _LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(monostate, monostate) noexcept { return true; } 47 48 # endif // _LIBCPP_STD_VER >= 20 49 50 template <> 51 struct _LIBCPP_TEMPLATE_VIS hash<monostate> { 52 using argument_type = monostate; 53 using result_type = size_t; 54 55 inline _LIBCPP_HIDE_FROM_ABI result_type operator()(const argument_type&) const _NOEXCEPT { 56 return 66740831; // return a fundamentally attractive random value. 57 } 58 }; 59 60 #endif // _LIBCPP_STD_VER >= 17 61 62 _LIBCPP_END_NAMESPACE_STD 63 64 #endif // _LIBCPP___VARIANT_MONOSTATE_H 65