[C++] Problem z funkcjami wirtualnymi, polimorfizmem

class Shape
{
public:
    virtual void shift( float x, float y ) = 0;
    virtual bool isColliding( Shape * shape );
};

class Circle
    : public Shape
{
public:
    bool isColliding( Circle * circle );
};

Shape * shape = new Circle( - 2, 0, 5 );
Circle * circle = new Circle( 5, 0, 5 );
shape->isColliding( circle ); //wywołuje z shape