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 <__config> 14 #include <__functional/hash.h> 15 #include <cstddef> 16 17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 18 #pragma GCC system_header 19 #endif 20 21 _LIBCPP_PUSH_MACROS 22 #include <__undef_macros> 23 24 _LIBCPP_BEGIN_NAMESPACE_STD 25 26 #if _LIBCPP_STD_VER > 14 27 28 struct _LIBCPP_TEMPLATE_VIS monostate {}; 29 30 inline _LIBCPP_INLINE_VISIBILITY 31 constexpr bool operator<(monostate, monostate) noexcept { return false; } 32 33 inline _LIBCPP_INLINE_VISIBILITY 34 constexpr bool operator>(monostate, monostate) noexcept { return false; } 35 36 inline _LIBCPP_INLINE_VISIBILITY 37 constexpr bool operator<=(monostate, monostate) noexcept { return true; } 38 39 inline _LIBCPP_INLINE_VISIBILITY 40 constexpr bool operator>=(monostate, monostate) noexcept { return true; } 41 42 inline _LIBCPP_INLINE_VISIBILITY 43 constexpr bool operator==(monostate, monostate) noexcept { return true; } 44 45 inline _LIBCPP_INLINE_VISIBILITY 46 constexpr bool operator!=(monostate, monostate) noexcept { return false; } 47 48 template <> 49 struct _LIBCPP_TEMPLATE_VIS hash<monostate> { 50 using argument_type = monostate; 51 using result_type = size_t; 52 53 inline _LIBCPP_INLINE_VISIBILITY 54 result_type operator()(const argument_type&) const _NOEXCEPT { 55 return 66740831; // return a fundamentally attractive random value. 56 } 57 }; 58 59 #endif // _LIBCPP_STD_VER > 14 60 61 _LIBCPP_END_NAMESPACE_STD 62 63 _LIBCPP_POP_MACROS 64 65 #endif // _LIBCPP___VARIANT_MONOSTATE_H 66