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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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