Overload distinct function pointers, function references, and monomorphic function objects into a single function object.

namespace boost {
  template<typename F1, typename F2, ... > class overloaded_function;
  template<typename F1, typename F2, ... > 
    overloaded_function< __function_type__< F1 >, __function_type__< F2 >,...> 
    make_overloaded_function(F1, F2, ...);
}