template<typename user_type, 
         template< typename, typename... > class PT = detail::no_policy, 
         typename... more_types> 
  struct impl_ptr;namespace boost {
  template<typename , typename  = void> struct is_impl_ptr;

  template<typename T> 
    struct is_impl_ptr<T, void_type< typename T::impl_ptr_type >>;

  typedef void void_type;
  typedef ::impl_ptr< U, P, M... > impl_ptr;
}