libcxx/include/__optional/nullopt_t.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___OPTIONAL_NULLOPT_T_H
#define _LIBCPP___OPTIONAL_NULLOPT_T_H

#include <__compare/ordering.h>
#include <__config>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

#if _LIBCPP_STD_VER >= 17

_LIBCPP_BEGIN_NAMESPACE_STD

struct nullopt_t {
  struct __secret_tag {
    explicit __secret_tag() = default;
  };
  _LIBCPP_HIDE_FROM_ABI constexpr explicit nullopt_t(__secret_tag, __secret_tag) noexcept {}

#  if _LIBCPP_STD_VER >= 20

  _LIBCPP_HIDE_FROM_ABI constexpr friend strong_ordering operator<=>(nullopt_t, nullopt_t) = default;

#  else

  _LIBCPP_HIDE_FROM_ABI constexpr friend bool operator==(nullopt_t, nullopt_t) noexcept { return true; }
  _LIBCPP_HIDE_FROM_ABI constexpr friend bool operator!=(nullopt_t, nullopt_t) noexcept { return false; }
  _LIBCPP_HIDE_FROM_ABI constexpr friend bool operator>(nullopt_t, nullopt_t) noexcept { return false; }
  _LIBCPP_HIDE_FROM_ABI constexpr friend bool operator<(nullopt_t, nullopt_t) noexcept { return false; }
  _LIBCPP_HIDE_FROM_ABI constexpr friend bool operator>=(nullopt_t, nullopt_t) noexcept { return true; }
  _LIBCPP_HIDE_FROM_ABI constexpr friend bool operator<=(nullopt_t, nullopt_t) noexcept { return true; }

#  endif // _LIBCPP_STD_VER >= 20
};

inline constexpr nullopt_t nullopt{nullopt_t::__secret_tag{}, nullopt_t::__secret_tag{}};

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_STD_VER >= 17

_LIBCPP_POP_MACROS
#endif // _LIBCPP___OPTIONAL_NULLOPT_T_H