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 > 14 25 26struct _LIBCPP_TEMPLATE_VIS monostate {}; 27 28_LIBCPP_HIDE_FROM_ABI constexpr bool operator==(monostate, monostate) noexcept { return true; } 29 30# if _LIBCPP_STD_VER > 17 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 > 17 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 > 17 49 50template <> 51struct _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 > 14 61 62_LIBCPP_END_NAMESPACE_STD 63 64#endif // _LIBCPP___VARIANT_MONOSTATE_H 65