In C++, is this method call static binding or dynamic binding?

Question

Here is the class definition:

class Shape { public:
    virtual void draw() = 0; ...
};
class Circle : public Shape {
    public:
        void draw() { ... }
... };
class Rectangle : public Shape { public:
    void draw() { ... } ...
};
class Square : public Rectangle {
    public:
        void draw() { ... }
... };

And here is the client code:

Square* sq = new Square; 
Rectangle* rect = new Rectangle; 
Shape* ptr_shape;
ptr_shape = sq;
ptr_shape->draw();
rect->draw();

A book that I was reading said the last statement is static binding:

However, the statement still looks dynamic binding to me because rect->draw should be called by the pointer in the "vtable" of rect in run-time.

Does anyone have ideas about whether the rect->draw is static binding or dynamic binding?

Answer 1

Rect::draw() is not final and rect is a pointer, so it uses dynamic binding.

But the compiler may use de-virtualization as optimization if all variables are in local scope and all types are known.

Answer 2

You're overall understanding of the vtable is correct.

I think what the book is trying to say is that the compiler might, and generally will, optimise the rect->draw to be called without going to the vtable.

In this case, the compiler can see that the rect is pointing to a Rectangle object.

In most production code, this will rarely be the case.