boost/gil/detail/std_common_type.hpp
//
// 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_GIL_DETAIL_STD_COMMON_TYPE_HPP
#define BOOST_GIL_DETAIL_STD_COMMON_TYPE_HPP
#include <type_traits>
#include <utility>
namespace boost { namespace gil { namespace detail {
// Defines a SFINAE-friendly version of `std::common_type`.
//
// Based on boost/hana/detail/std_common_type.hpp
// 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 std::decay
<
decltype(true ? std::declval<T>() : std::declval<U>())
>::type;
};
}}} // namespace boost::gil::detail
#endif