C++ Comparing descendants of abstract class

Question

Yes, I know it's bad tone to compare different descendants of abstract class. But I really have to.

I have this simple abstract class:

class Figure {
    public:
    virtual double Square() = 0;
    virtual ~Figure() {};
}

What I want to add to it is something like:

bool operator<(const Figure& other) {};

Which would compare its descendants - geometric figures, namely Triangle, Rectangle, Octagon - using their area returned in method Square().

Is that possible in any way?

Answer 1

From your comment return (*this->Square() < other->Square()); your trouble simply seems to be basic syntax.

this is a simple pointer. So the typical correct syntax is just this->Square(). Of course since it's inside a member function then this can be omitted entirely as just Square().

other is a reference, so that uses the dot operator as other.Square()

Another useful thing, potentially relevant to your latest comment, is to make the operator< function const since it isn't modifying the the object it's being called on.

So the resulting code should be something more like:

bool operator<(const Figure& other) const
{
    return Square() < other.Square();
}