boost/type_traits/detail/common_type_impl.hpp

#ifndef BOOST_TYPE_TRAITS_DETAIL_COMMON_TYPE_IMPL_HPP_INCLUDED
#define BOOST_TYPE_TRAITS_DETAIL_COMMON_TYPE_IMPL_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/type_traits/detail/common_arithmetic_type.hpp>
#include <boost/type_traits/detail/composite_pointer_type.hpp>
#include <boost/type_traits/detail/composite_member_pointer_type.hpp>
#include <boost/type_traits/type_identity.hpp>
#include <boost/type_traits/is_class.hpp>
#include <boost/type_traits/is_union.hpp>
#include <boost/type_traits/is_convertible.hpp>
#include <boost/type_traits/is_pointer.hpp>
#include <boost/type_traits/is_member_pointer.hpp>
#include <boost/type_traits/conditional.hpp>
namespace boost
{
namespace type_traits_detail
{
// the arguments to common_type_impl have already been passed through decay<>
template<class T, class U> struct common_type_impl;
// same type
template<class T> struct common_type_impl<T, T>
{
    typedef T type;
};
// one of the operands is a class type, try conversions in both directions
template<class T, class U> struct ct_class
{
    BOOST_STATIC_CONSTANT( bool, ct = boost::is_class<T>::value || boost::is_union<T>::value );
    BOOST_STATIC_CONSTANT( bool, cu = boost::is_class<U>::value || boost::is_union<U>::value );
    BOOST_STATIC_CONSTANT( bool, value = ct || cu );
};
template<class T, class U> struct common_type_impl3;
template<class T, class U> struct common_type_class: public boost::conditional<
    boost::is_convertible<T, U>::value && !boost::is_convertible<U, T>::value,
    boost::type_identity<U>,
    typename boost::conditional<
        boost::is_convertible<U, T>::value && !boost::is_convertible<T, U>::value,
        boost::type_identity<T>,
        common_type_impl3<T, U>
    >::type
>::type
{
};
template<class T, class U> struct common_type_impl: public boost::conditional<
    ct_class<T, U>::value,
    common_type_class<T, U>,
    common_type_impl3<T, U> >::type
{
};
// pointers
template<class T, class U> struct common_type_impl4;
template<class T, class U> struct common_type_impl3: public boost::conditional<
    boost::is_pointer<T>::value || boost::is_pointer<U>::value,
    composite_pointer_type<T, U>,
    common_type_impl4<T, U> >::type
{
};
// pointers to members
template<class T, class U> struct common_type_impl5;
template<class T, class U> struct common_type_impl4: public boost::conditional<
    boost::is_member_pointer<T>::value || boost::is_member_pointer<U>::value,
    composite_member_pointer_type<T, U>,
    common_type_impl5<T, U> >::type
{
};
// arithmetic types (including class types w/ conversions to arithmetic and enums)
template<class T, class U> struct common_type_impl5: public common_arithmetic_type<T, U>
{
};
} // namespace type_traits_detail
} // namespace boost
#endif // #ifndef BOOST_TYPE_TRAITS_DETAIL_COMMON_TYPE_IMPL_HPP_INCLUDED