pfr/detail/fake_object.hpp

0001 // Copyright (c) 2023 Bela Schaum, X-Ryl669, Denis Mikhailov.
0002 //
0003 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0004 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0005
0006
0007 // Initial implementation by Bela Schaum, https://github.com/schaumb
0008 // The way to make it union and UB free by X-Ryl669, https://github.com/X-Ryl669
0009 //
0010
0011 #ifndef BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
0012 #define BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
0013 #pragma once
0014
0015 #include <boost/pfr/detail/config.hpp>
0016
0017 namespace boost { namespace pfr { namespace detail {
0018
0019 // This variable serves as a compile-time assert. If you see any error here, then
0020 // you're probably using `boost::pfr::get_name()` or `boost::pfr::names_as_array()` with a non-external linkage type.
0021 template <class T>
0022 extern const T passed_type_has_no_external_linkage;
0023
0024 // For returning non default constructible types, it's exclusively used in member name retrieval.
0025 //
0026 // Neither std::declval nor boost::pfr::detail::unsafe_declval are usable there.
0027 // Limitation - T should have external linkage.
0028 template <class T>
0029 constexpr const T& fake_object() noexcept {
0030     return passed_type_has_no_external_linkage<T>;
0031 }
0032
0033 }}} // namespace boost::pfr::detail
0034
0035 #endif // BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
0036