C / C++ / MFC

class adder
{
    public:
        int add( int i, int j ) const { return i + j; }
};

int main()
{
    std::cout << adder().add( 12, 34 ) << std::endl;
}

class adder
{
     public:
        virtual int add( int i, int j ) = 0;
};

class minimal_adder
{
    public:
        virtual int add( int, int ) { return 0; }
};

class CMyBaseFormView : public CFormView
{
public:
  virtual void ViewMethod() = 0; // to be overwritten only :)
};

class CMyFormView1 : public CMyBaseFormView
{
public:
  virtual void ViewMethod() { /* I have to control my own IDs :) */ };
};

class CMyFormView2 : public CMyBaseFormView
{
public:
  virtual void ViewMethod() { /* I have to control my own IDs :) */ };
};

//
void CMyGenericClass::MyMethod(... , CMyBaseFormView* pcView)
{
  if (pcView->GetSafeHwnd()) {
    pcView->ViewMethod(); // one call for all forms :)
  }
}