/*!
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@file
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Defines a SFINAE-friendly version of `std::common_type`.
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@copyright Louis Dionne 2013-2017
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_DETAIL_STD_COMMON_TYPE_HPP
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#define BOOST_HANA_DETAIL_STD_COMMON_TYPE_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/detail/decay.hpp>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN namespace detail {
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//! @ingroup group-details
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//! Equivalent to `std::common_type`, except it is SFINAE-friendly and
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//! does not support custom specializations.
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template <typename T, typename U, typename = void>
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struct std_common_type { };
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template <typename T, typename U>
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struct std_common_type<T, U, decltype((void)(
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true ? std::declval<T>() : std::declval<U>()
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))> {
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using type = typename detail::decay<
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decltype(true ? std::declval<T>() : std::declval<U>())
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>::type;
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};
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} BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_DETAIL_STD_COMMON_TYPE_HPP
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