Changing signature while Overriding in C++

Question

I have a base class

class Shape{
    public:
        virtual int getArea()=0;
}

I want to change the signature while overriding like this:

class Rectangle : class Shape{
    public:
        int getArea(int someParameter = 0){
            return 0;
        }
}

Is it possible somehow to achieve this, as I am using default value for newly added parameter?

If you change signature you are no longer overriding, you are overloading. And no, it's no longer possible to use polymorphism as `Shape::getArea` and `Rectangle::getArea` are two different functions. — Some programmer dude, Jun 11 '15 at 06:26
@JoachimPileborg: I understand that, but is there any way out? — Kumar, Jun 11 '15 at 06:27
@Abhinav : This is not possible. you can get some come information here http://stackoverflow.com/questions/411103/function-with-same-name-but-different-signature-in-derived-class — Spanky, Jun 11 '15 at 06:29
You could probably get away by defining a separate hierarchy of "AreaParameter", declaring the virtual taking a pointer or a reference to such parameter (`virtual int getArea(const AreaParameter &p = AreaParameter())`), doing a real override in the subclass and in there downcast the parameter type. (Or in general by employing any double dispatch technique...) — peppe, Jun 11 '15 at 06:31

score 4 · Accepted Answer · answered Jun 11 '15 at 06:30

4

The only solution I can see is that you implement both int getArea() and int getArea(int), where one function can call the other (for example int getArea() { return getArea(0); }). You can not have the overload taking an argument have a default argument then.

answered Jun 11 '15 at 06:30

Some programmer dude

400,186
35
402
621

score 0 · Answer 2 · answered Jun 27 '20 at 08:23

You need to overload your virtual function. But if you overloaded virtual function, you will get a warning "hides overloaded virtual function"

Solution is override function with native signature and overload it with virtual prefix.

Example:

class A {
   virtual void foo(int) {...}
};

class B: public A {
   void foo(int i) override {
       A::foo(i);
   }
   
   virtual void foo(const std::string& str) {
       ...
   }
};

Changing signature while Overriding in C++

2 Answers2