move_if_rr

#include <boost/mpl/if.hpp>
#include <boost/mpl/not.hpp>
#include <boost/mpl/or.hpp>
#include <boost/type_traits/is_const.hpp>
#include <boost/type_traits/is_reference.hpp>
#include <boost/type_traits/remove_reference.hpp>

namespace Impl
{
    using namespace boost;

    //! Evaluates to true if T has move semantics inside forwarding function.
    template< class T >
    struct is_rr
        :   mpl::not_< mpl::or_< is_reference< T >, is_const< typename remove_reference< T >::type > > >
    {
    };

    template< class U, class T >
    struct move_if_rr_helper
        :   mpl::if_< is_rr< U >, typename remove_reference< T >::type &&, T & >
    {
    };
}

//! Moves rr if U && has move semantics inside forwarding function.
template< class U, class T >
inline typename Impl::move_if_rr_helper< U, T >::type move_if_rr( T &&rr )
{
    return static_cast< typename Impl::move_if_rr_helper< U, T >::type >( rr );
}