58 lines
1.7 KiB
C++
58 lines
1.7 KiB
C++
// Copyright (c) 2023 Bela Schaum, X-Ryl669, Denis Mikhailov.
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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// Initial implementation by Bela Schaum, https://github.com/schaumb
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// The way to make it union and UB free by X-Ryl669, https://github.com/X-Ryl669
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//
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#ifndef BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
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#define BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
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#pragma once
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#include <boost/pfr/detail/config.hpp>
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#ifdef __clang__
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# pragma clang diagnostic push
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# pragma clang diagnostic ignored "-Wundefined-internal"
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# pragma clang diagnostic ignored "-Wundefined-var-template"
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#elif defined(__GNUC__)
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# pragma GCC diagnostic push
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# pragma GCC diagnostic ignored "-Wundefined-var-template"
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#endif
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namespace boost { namespace pfr { namespace detail {
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// This class has external linkage while T has not sure.
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template <class T>
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struct wrapper {
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const T value;
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};
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// This variable servers as a link-time assert.
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// If linker requires it, then `fake_object()` is used at runtime.
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template <class T>
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extern const wrapper<T> do_not_use_PFR_with_local_types;
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// For returning non default constructible types, it's exclusively used in member name retrieval.
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//
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// Neither std::declval nor boost::pfr::detail::unsafe_declval are usable there.
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// This takes advantage of C++20 features, while boost::pfr::detail::unsafe_declval works
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// with the former standards.
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template <class T>
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constexpr const T& fake_object() noexcept {
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return do_not_use_PFR_with_local_types<T>.value;
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}
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}}} // namespace boost::pfr::detail
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#ifdef __clang__
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# pragma clang diagnostic push
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#elif defined(__GNUC__)
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# pragma GCC diagnostic pop
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#endif
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#endif // BOOST_PFR_DETAIL_FAKE_OBJECT_HPP
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