Re: Copy of derived object from pointer to base

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From: Larry Brasfield (donotspam_larry_brasfield_at_hotmail.com)
Date: 10/12/04 

Date: Tue, 12 Oct 2004 09:13:13 -0700

[minor improvement suggested below]

"Sigurd Stenersen" <sigurds@utvikling.com> wrote in message
 news:OXrYI$GsEHA.2776@TK2MSFTNGP14.phx.gbl...

[regarding how a virtual copy method would appear]

[I take a little liberty with quotes here, applying Sigurd's
 correction to his earlier (quoted) post for clarity.]

> class Base
> {
> public:
> virtual Base *Clone() { return new Base(*this); }
> };
>
> class Derived : public Base
> {
#if 0
> virtual Base *Clone() { return new Derived(*this); }
#endif

      virtual Derived *Clone() { return new Derived(*this); }
> };

The reason to return a pointer whose type is pointer to the
derived class is to make the Clone() method usable, without
casting, when the result is known to be a subclass of Base.
For example:

void Fiddle(Derived & d)
{
   Derived * pAnother = d.Clone();
}

Proper support of this long time C++ feature came late
to MSVC++, arriving with v7. 

-- 
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

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