I want to make an interface in C++.
How can I get op2.radius value in operator overloading statement?
I'd like that Comparable Class can be used for others such as Rectangle, Line etc.

```
#include <iostream>
using namespace std;

class Comparable {
      public:
             virtual bool operator > (Comparable& op2)=0;
             //virtual bool operator < (Comparable& op2)=0;
             //virtual bool operator == (Comparable& op2)=0;
};

class Circle : public Comparable {
      int radius;
      public:
             Circle(int radius=1) { this->radius = radius; }
             int getRadius() { return radius; }
             bool operator > (Comparable& op2)
             {
                  if (radius > op2.radius) // <-- here!
                  return true;
                  else
                  return false;
             }

};

template <class T>
T bigger(T a, T b){
           if (a > b) return a;
           else
           return b;
}

void main()
{
    Circle waffle(10), pizza(20), y;
    y = bigger(waffle, pizza);
    cout << "the bigger one is " << y.getRadius() << endl;
}

```