完美轉發僅僅發生於當呼叫該函式時會發生型別推倒
如

template<typename T>
void test(T&&a){

} 

如下情況CallService並不會發生完美轉發

template<typename R,typename ...Paras>
class ServiceClient
{
    ReturnType<R> _returnVal;
    ParameterType<Paras...>_parameters;
  std::string _serviceName;
public:


   //this not a universival reference because this Paras is not dedeced in this function
  //but deduced in the class
    R CallService(const Paras&... p){

        Serializer Is;

        _parameters.serialize(&Is, p...);

        std::string s(Is.data(),Is.size());
        std::tuple<Paras...> items;
        int a;



        using args_type = std::tuple<typename std::decay<Paras>::type...>;

        Serializer ds(StreamBuffer(s.c_str(), s.size()));
        constexpr auto N = std::tuple_size<typename std::decay<args_type>::type>::value;
        args_type args = ds.get_tuple < args_type > (std::make_index_sequence<N>{});


         ++a;
         //get the serize parameters use _parameters
        //send to server
        //get the replay string
        //use _returnval  to un serlize the parameters from replay string
        //then get the ret val


    }




    R ServiceFunc(Paras&& ...p){

    }

    ServiceClient(std::string name){
        _serviceName = name;
        //get the service signature 
    }
};

 

原因是CallService的函式引數型別在定義 ServiceClient時就已經確定，此時在呼叫CallService不會發生型別推導。