How to use stateless class derived from a virtual base class in a templated class. A strategy I use in many code

stateless_derivation_and_template.cpp

#include <iostream>

class master_virtual
{
public: 
    virtual void msg() {return;}
};

class derived_hi : public master_virtual
{
public:
    void msg() {std::cout << "Hi from derived\n";}
};


class derived_hey : public master_virtual
{
public:
    void msg() {std::cout << "Hey from derived\n";}
};


template <class TYPE_A> 
class greeter
{
protected:
  TYPE_A msg_class; 
public:
  void greet()
  {
    msg_class.msg();
  }
};


int main(int argc, char const *argv[])
{
    greeter<derived_hi> hi;
    hi.greet(); // Hi from derived
    greeter<derived_hey> hey;
    hey.greet();  // Hey from derived
    return 0;
}

A nice perk is that the greeter class can live in another header file, unaware of derived classes.