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