boost/none_t.hpp
// Copyright (C) 2003, Fernando Luis Cacciola Carballal. // Copyright (C) 2014, 2024 Andrzej Krzemienski. // // Use, modification, and distribution is subject to the Boost Software // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) // // See http://www.boost.org/libs/optional for documentation. // // You are welcome to contact the author at: // fernando_cacciola@hotmail.com // #ifndef BOOST_NONE_T_17SEP2003_HPP #define BOOST_NONE_T_17SEP2003_HPP #include <boost/config.hpp> #include <boost/config/pragma_message.hpp> #if defined (BOOST_NO_CXX11_RVALUE_REFERENCES) || defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) \ || defined(BOOST_NO_CXX11_LAMBDAS) || defined(BOOST_NO_CXX11_DECLTYPE_N3276) \ || defined(BOOST_NO_CXX11_DELETED_FUNCTIONS) || defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) \ || defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS) || defined(BOOST_NO_CXX11_STATIC_ASSERT) #error "Boost.Optional requires some C++11 features since version 1.87. If you have an older C++ version use Boost.Optional version 1.86 or earlier." #elif defined(BOOST_NO_CXX11_REF_QUALIFIERS) || defined(BOOST_NO_CXX11_NOEXCEPT) || defined(BOOST_NO_CXX11_DEFAULTED_MOVES) BOOST_PRAGMA_MESSAGE("C++03 support is deprecated in Boost.Optional 1.83 and will be removed in Boost.Optional 1.88.") #endif namespace boost { #ifdef BOOST_OPTIONAL_USE_OLD_DEFINITION_OF_NONE namespace detail { struct none_helper{}; } typedef int detail::none_helper::*none_t ; #elif defined BOOST_OPTIONAL_USE_SINGLETON_DEFINITION_OF_NONE class none_t {}; #else struct none_t { struct init_tag{}; explicit BOOST_CONSTEXPR none_t(init_tag){} // to disable default constructor }; #endif // old implementation workarounds } // namespace boost #endif // header guard