Pointer to class data member “::*”

Question

I came across this strange code snippet which compiles fine:

class Car
{
    public:
    int speed;
};

int main()
{
    int Car::*pSpeed = &Car::speed;
         


        

Answer 1

You can later access this member, on any instance:

int main()
{    
  int Car::*pSpeed = &Car::speed;    
  Car myCar;
  Car yourCar;

  int mySpeed = myCar.*pSpeed;
  int yourSpeed = yourCar.*pSpeed;

  assert(mySpeed > yourSpeed); // ;-)

  return 0;
}

Note that you do need an instance to call it on, so it does not work like a delegate.
It is used rarely, I've needed it maybe once or twice in all my years.

Normally using an interface (i.e. a pure base class in C++) is the better design choice.