#include <boost/mpl/tag.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>
+#include <boost/type_traits/is_const.hpp>
#include <boost/type_traits/add_const.hpp>
+#include <boost/type_traits/add_reference.hpp>
#include <boost/typeof/typeof.hpp>