template<typename OutSignature> 
struct default_signal_args {
  // types
  typedef boost::last_value< typename boost::function_traits< OutSignature >::result_type > combiner_type;     
  typedef int                                                                               group_type;        
  typedef std::less< group_type >                                                           group_compare_type;
  typedef signal_args< combiner_type, group_type, group_compare_type >                      type;              
};