// In header: <boost/proto/transform/arg.hpp>


struct _void :  proto::transform< _void > {
  // member classes/structs/unions
  template<typename Expr, typename State, typename Data> 
  struct impl :  proto::transform_impl< Expr, State, Data > {
    // types
    typedef void result_type;

    // public member functions
    void operator()(typename impl::expr_param, typename impl::state_param, 
                    typename impl::data_param) const;
  };
};