Re: Virtual constructor?

From:

Seungbeom Kim <musiphil@bawi.org>

Newsgroups:

comp.lang.c++.moderated

Date:

4 Jun 2006 09:17:03 -0400

Message-ID:

<e5tt7u$j7r$1@news.Stanford.EDU>

Rob wrote:

A constructor cannot be virtual.

As I said.

However, let's say we have;

class X
{
     public:
        virtual X *Clone() const = 0;
};

class Y : public X
{
     public:
        virtual Y *Clone() const {return new Y(*this);};
}

This technique/idiom is often referred to as the "virtual copy
constructor".

As I said, and even mentioned an FAQ item describing exactly that.

A better name needed to avoid confusion like yours,
but that's life: we humans have to cope with ambiguity.

I didn't have any confusion. I said:

"If 'virtual' is used in the strict sense defined by the language, there
can be no virtual constructors of any kind, whether default constructors
or copy constructors. Otherwise, if it's used to mean an idiom, you
*can* implement a virtual default constructor just as a virtual copy
constructor: something that depends on an existing object and creates a
new one of the same type."

If there's anything unclear in this explanation, let me know
(explicitly). Otherwise, did you actually read what you replied to?

--
Seungbeom Kim

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]