// Copyright (c) 2019-2020 Antony Polukhin.
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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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#ifndef BOOST_PFR_DETAIL_UNSAFE_DECLVAL_HPP
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#define BOOST_PFR_DETAIL_UNSAFE_DECLVAL_HPP
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#include <boost/pfr/detail/config.hpp>
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#include <type_traits>
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namespace boost { namespace pfr { namespace detail {
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// This function serves as a link-time assert. If linker requires it, then
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// `unsafe_declval()` is used at runtime.
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void report_if_you_see_link_error_with_this_function() noexcept;
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// For returning non default constructible types. Do NOT use at runtime!
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//
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// GCCs std::declval may not be used in potentionally evaluated contexts,
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// so we reinvent it.
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template <class T>
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constexpr T unsafe_declval() noexcept {
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report_if_you_see_link_error_with_this_function();
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typename std::remove_reference<T>::type* ptr = 0;
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ptr += 42; // suppresses 'null pointer dereference' warnings
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return static_cast<T>(*ptr);
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}
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}}} // namespace boost::pfr::detail
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#endif // BOOST_PFR_DETAIL_UNSAFE_DECLVAL_HPP
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