The difficulty of implementing the result_of protocol has always bothered me. I've often found myself writing a primary result<...> template and several specializations to handle different cv-qualifications, and I've still not felt that I was doing it quite right. It's lucky that operator() has to be a member function, or I'd be worried about capturing the r/lvalue-ness of the function object itself. Now I just ran into another issue, from the other side of the result_of interface. If I have a function template taking a function object argument by reference, and I want to use result_of with it, I need to do something special to account for the case where I've been passed a function reference. To wit: template <class F> typename result_of<F()>::type call(F const& f) { return f(); } int f() { return 0; } int x = call(f); The problem is that in the above case, F is deduced as int(), and we form an illegal function type (one that itself returns a function type) in result_of<F()>::type. To deal with this I need something more like template <class F> typename result_of< typename mpl::if_< is_class<F> , F , typename add_pointer<F>::type >::type() >::type call(F const& f) { return f(); } Is there an easier way? -- Dave Abrahams Boost Consulting http://boost-consulting.com