How to add a template to an non templated C++ class? [closed]

Below snippet 1 worked as desired. However when I tried to to covert Sender to a templated one (snippet 2), I keep getting compiler errors. The goal is to get this working with minimal changes, so preferable keep the <double> and <int> specific implementations, but keep DUMMY generic. Is this possible?

Snippet 1: Untemplated Sender -> Works

#include <iostream>

class Sender {
   public:
     void send(double d) const {
        std::cout <<"Send double "<<d<<std::endl;
     }
     void send(int i) const {
        std::cout << "Send int "<<i<<std::endl;
     }
};

template<typename T>
class DataObject {
   T data;
  public:
   DataObject(T ldata) : data(ldata) {}
   void send(const Sender& s);
};

template<>
void DataObject<double>::send(const Sender& sender) {
   sender.send(data);
}

template<>
void DataObject<int>::send(const Sender& sender) {
   sender.send(data);
}

int main() {
  Sender sender;
  DataObject<double> obj(1.0);
  DataObject<int> obj2(2);
  obj.send(sender);
  obj2.send(sender);
  return 0;
}

Snippet 2: Templated Sender -> Compiler Errors

#include <iostream>

template<typename DUMMY>
class Sender {
   DUMMY dummy;
   public:
     Sender(const DUMMY& ldummy) : dummy(ldummy) {}
     void send(double d) const {
        std::cout << dummy <<" - Send double "<<d<<std::endl;
     }
     void send(int i) const {
        std::cout << dummy << " - Send int "<<i<<std::endl;
     }
};

template<typename T,typename DUMMY>
class DataObject {
   T data;
  public:
   DataObject(T ldata) : data(ldata) {}
   void send(const Sender<DUMMY>& s);
};

template<typename DUMMY>
void DataObject<double>::send(const Sender<DUMMY>& sender) {
   sender.send(data);
}

template<typename DUMMY>
void DataObject<int>::send(const Sender<DUMMY>& sender) {
   sender.send(data);
}

int main() {
  Sender<std::string> sender("Dummy");
  DataObject<double> obj(1.0);
  DataObject<int> obj2(2);
  obj.send(sender);
  obj2.send(sender);
  return 0;
}