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#ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED
#define BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED
//
// Copyright 2015 Peter Dimov
//
// Distributed under the Boost Software License, Version 1.0.
// See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt
//
#include <boost/config.hpp>
#include <boost/type_traits/decay.hpp>
#include <boost/type_traits/declval.hpp>
#include <boost/detail/workaround.hpp>
#if defined(BOOST_NO_CXX11_DECLTYPE)
#include <boost/type_traits/detail/common_type_impl.hpp>
#endif
#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
#include <boost/type_traits/detail/mp_defer.hpp>
#endif
namespace boost
{
// variadic common_type
#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
template<class... T> struct common_type
{
};
#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
template<class... T> using common_type_t = typename common_type<T...>::type;
namespace type_traits_detail
{
template<class T1, class T2, class... T> using common_type_fold = common_type_t<common_type_t<T1, T2>, T...>;
} // namespace type_traits_detail
template<class T1, class T2, class... T>
struct common_type<T1, T2, T...>: type_traits_detail::mp_defer<type_traits_detail::common_type_fold, T1, T2, T...>
{
};
#else
template<class T1, class T2, class... T>
struct common_type<T1, T2, T...>: common_type<typename common_type<T1, T2>::type, T...>
{
};
#endif // !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
#else
template<
class T1 = void, class T2 = void, class T3 = void,
class T4 = void, class T5 = void, class T6 = void,
class T7 = void, class T8 = void, class T9 = void
>
struct common_type: common_type<typename common_type<T1, T2>::type, T3, T4, T5, T6, T7, T8, T9>
{
};
#endif // !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
// one argument
template<class T> struct common_type<T>: boost::decay<T>
{
};
// two arguments
namespace type_traits_detail
{
// binary common_type
#if !defined(BOOST_NO_CXX11_DECLTYPE)
#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
#if !defined(BOOST_MSVC) || BOOST_MSVC > 1800
// internal compiler error on msvc-12.0
template<class T1, class T2> using builtin_common_type = typename boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )>::type;
template<class T1, class T2> struct common_type_impl: mp_defer<builtin_common_type, T1, T2>
{
};
#else
template<class T1, class T2> using builtin_common_type = decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() );
template<class T1, class T2> struct common_type_impl_2: mp_defer<builtin_common_type, T1, T2>
{
};
template<class T1, class T2> using decay_common_type = typename boost::decay<typename common_type_impl_2<T1, T2>::type>::type;
template<class T1, class T2> struct common_type_impl: mp_defer<decay_common_type, T1, T2>
{
};
#endif // !defined(BOOST_MSVC) || BOOST_MSVC > 1800
#else
template<class T1, class T2> struct common_type_impl: boost::decay<decltype( boost::declval<bool>()? boost::declval<T1>(): boost::declval<T2>() )>
{
};
#endif // #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES) && !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
#endif // #if !defined(BOOST_NO_CXX11_DECLTYPE)
// decay helper
template<class T1, class T2, class T1d = typename boost::decay<T1>::type, class T2d = typename boost::decay<T2>::type> struct common_type_decay_helper: boost::common_type<T1d, T2d>
{
};
template<class T1, class T2> struct common_type_decay_helper<T1, T2, T1, T2>: common_type_impl<T1, T2>
{
};
} // type_traits_detail
template<class T1, class T2> struct common_type<T1, T2>: type_traits_detail::common_type_decay_helper<T1, T2>
{
};
} // namespace boost
#endif // #ifndef BOOST_TYPE_TRAITS_COMMON_TYPE_HPP_INCLUDED
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