Thread: polymorphism and inheritance

Originally Posted by stewie griffin

At first I didn't use switch:

Code:

ostream& operator << (ostream& os, const Drawing& drw)
 {
     for(int i=0; i<drw.size_;i++)
          if (!(drw.drawing_[i].is_empty()))
 	os << drw.drawing_[i]<<endl;
     return os<<endl;
 }

I have operator << for each type of shape that prints what it needs
I thought that was enough

The problem with overloaded operators is that they are not virtual. So to solve that, I'd suggestion you do something like this:

Code:

class Shape
{
...
  public:
...
     virtual void Draw(ostream& os) = 0;
};

class Line : public Shape
{
... 
   public:
...
     virtual void Draw(ostream& os);
};

void Line::Draw(ostream &os)
{
    ... do your ACTUAL drawing for line, using basic << operator.
}

ostream& operator << (ostream& os, const Shape& sh)
 {
     sh.Draw(os);
     return os;
 }

That way, each drawing can do it's own thing, but you can still use a generic form with << .

--
Mats