Re: constructors as virtual

Rolf Magnus <>
Wed, 02 Jan 2008 19:32:22 +0100
Rahul wrote:

Hi Everyone,

  I understand that the constructors can't be virtual

Good. Do you also understand why?

  and parashift has the following example, to have an workaround for the
  constructors to be virtual,

IMHO, that is not really a good description for what that example does.

 class Shape {
   virtual ~Shape() { } // A virtual destructor
   virtual void draw() = 0; // A pure virtual function
   virtual void move() = 0;
   virtual Shape* clone() const = 0; // Uses the copy constructor
   virtual Shape* create() const = 0; // Uses the default

 class Circle : public Shape {
   Circle* clone() const; // Covariant Return Types; see below
   Circle* create() const; // Covariant Return Types; see below

 Circle* Circle::clone() const { return new Circle(*this); }
 Circle* Circle::create() const { return new Circle(); }

Now, new Circle() would create a Circle object, and the constructor of
bsae class Shape would be called first before Circle right? So how
does it offer to be a workaround for the constructors being virtual?

For that, you would first have to explain what you would expect from
a "virtual constructor", since such a concept wouldn't make any sense in

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