Hi again, With BOOST_TYPEOF in place, the mpl operators (boost::mpl::plus etc) could be augmented by actual operators( + etc) As below:---> Whats the point of this? Well first its fun and more legible and second brings mpl further into runtime programming. Maybe also fits in with Alexey Gurtovoys round lambda: http://thread.gmane.org/gmane.comp.lib.boost.devel/77267 /* Example */ #include <boost/utility/enable_if.hpp> #include <boost/typeof/typeof.hpp> #include <boost/mpl/plus.hpp> #include <boost/mpl/int.hpp> #include <boost/mpl/or.hpp> // a useful addition to BOOST_TYPEOF ? #define BOOST_AUTO_TYPEDEF(name, expr) typedef BOOST_TYPEOF(expr) name #define BOOST_AUTO_TYPEDEF_TPL(name, expr) typedef BOOST_TYPEOF_TPL(expr) name namespace boost{namespace mpl { // naive implementation of is_integral for demo only template <typename T> struct is_integral_c :false_{}; template <int N> struct is_integral_c<int_<N> > : true_{}; template <int N> struct is_integral_c<integral_c<int,N> > : true_{}; template <typename Lhs, typename Rhs> typename boost::enable_if< boost::mpl::or_< is_integral_c<Lhs>, is_integral_c<Rhs> >, typename plus<Lhs,Rhs>::type >::type operator + (Lhs lhs, Rhs rhs) { BOOST_AUTO_TYPEDEF_TPL(result, Lhs() + Rhs()); return result() ; }; }}//boost::mpl #include <iostream> int main() { typedef boost::mpl::int_<1> one; typedef boost::mpl::int_<2> two; typedef boost::mpl::int_<3> three; typedef boost::mpl::int_<4> four; BOOST_AUTO_TYPEDEF(result , one() + two() + three() + four() ) ; std::cout << typeid(result).name() <<'\n'; std::cout << one() + two() + three() + four() <<'\n'; } reagrds Andy Little