Question

I am implementing polymorphic protocol handlers and in my base class I want to have a pure virtual function where the template function parameter is unspecified. But my compiler is complaining. I guess this cannot be done. Anyone any suggestions on how to achieve this? If at all possible? Otherwise I will have to scrap the polymorphic idea.

Here is my code which gives me error C2976 ‘ProtoWrapper’ : too few template arguments. compiler=MSVC++2008.

#include "smartptrs.hpp"
#include <iostream>

class realproto {
public:
   const char* getName() const { return "realproto"; }
}; 

class real2ndproto {
public:
   const char* get2Name() const { return "real2ndproto"; }
}; 


template<typename T>
class ProtoWrapper : public ref_type {
public:
   ProtoWrapper(T* real) : m_msg(real) {}
   ~ProtoWrapper() { delete m_msg; }  //cannot have smart ptr on real_proto - so do this way

   T* getMsg() { return m_msg; }

private:
   T* m_msg;
};


class ProtocolDecoder 
{
public:
  virtual void Parse(ProtoWrapper<>* decoded_msg) = 0;  //problem line - compile error
};

class CSTA2Decoder  : public ProtocolDecoder
{
public:
   virtual void Parse(ProtoWrapper<realproto>* decoded_msg) {
      realproto* pr = decoded_msg->getMsg();
      std::cout << pr->getName() << std::endl;
   }
};


int main(int argc, char* argv[])
{
   {
      ref_ptr<ProtoWrapper <realproto> > msg2 = new ProtoWrapper<realproto>(new realproto);

      realproto* pr1 = msg2->getMsg();

      std::cout << "created new realproto\n";
   } 

    return 0;
}

Answer 1

To pull this off, you need to turn ProtocolDecoder into a class template:

template <typename T>
class ProtocolDecoder 
{
public:
  virtual void Parse(ProtoWrapper<T>* decoded_msg) = 0;  //problem line - compile error
};

class CSTA2Decoder  : public ProtocolDecoder<realproto>
{
  //...
};