namespace boost {
  namespace signals {
    template<typename Input, typename Output> 
      struct connect_impl<Input, Output>;
    template<typename Signature, typename Combiner, typename Group, 
             typename GroupCompare> 
      struct is_component<boost::signal< Signature, Combiner, Group, GroupCompare >>;
    template<typename Signature, typename Combiner, typename Group, 
             typename GroupCompare> 
      struct get_signal<boost::signal< Signature, Combiner, Group, GroupCompare >>;
    template<typename Signature, typename Combiner, typename Group, 
             typename GroupCompare> 
      struct get_signal_type<boost::signal< Signature, Combiner, Group, GroupCompare >>;
    template<typename Signature, typename T> 
      struct get_slot<Signature, T, typename boost::enable_if< detail::result_of_defined< typename detail::replace_return_type< Signature, T >::type > >::type>;
  }
}