c++ - Override number of parameters of pure virtual functions

Question

I have implemented the following interface:

template <typename T>
class Variable
{
public:
  Variable (T v) : m_value (v) {}
  virtual void Callback () = 0;
private:
  T m_value;
};

A proper derived class would be defined like this:

class Derived : public Variable<int>
{
public:
  Derived (int v) : Variable<int> (v) {}
  void Callback () {}
};

However, I would like to derive classes where Callback accepts different parameters (eg: void Callback (int a, int b)). Is there a way to do it?

Answer 1

This is a problem I ran in a number of times.

This is impossible, and for good reasons, but there are ways to achieve essentially the same thing. Personally, I now use:

struct Base
{
  virtual void execute() = 0;
  virtual ~Base {}
};

class Derived: public Base
{
public:
  Derived(int a, int b): mA(a), mB(b), mR(0) {}

  int getResult() const { return mR; }

  virtual void execute() { mR = mA + mB; }

private:
  int mA, mB, mR;
};

In action:

int main(int argc, char* argv[])
{
  std::unique_ptr<Base> derived(new Derived(1,2));
  derived->execute();
  return 0;
} // main