Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!yale!slb-sdr!saito
From: saito@sdr.slb.com (Naoki Saito)
Newsgroups: comp.lang.c++
Subject: virtual assignment operator is possible?
Keywords: assignment operator, virtual function
Message-ID: <1989Dec30.174745.8174@sdr.slb.com>
Date: 30 Dec 89 17:47:45 GMT
Reply-To: saito@slb-sdr.UUCP ()
Organization: Schlumberger-Doll Research, Ridgefield CT
Lines: 36


	Suppose I have a base class B, and its derived class D.  In each class,
I defined assignment operator, i.e, X& operator=(X&).  Then,

B* pb0 = new B();
B* pb1 = new B();
D* pd0 = new D();
D* pd1 = new D();

*pb1 = *pb0 // B& operator=(B&) is invoked.
*pd1 = *pd0 // D& operator=(D&) is invoked.

This is perfectly fine.  However,

B* pdb0 = new D();
B* pdb1 = new D();

*pdb1 = *pdb0 // B& operator=(B&) is invoked.

I want to use D& operator=(D&) in the above case.  Of course, it is possible to
do this by explicit casting:

*((D*)pdb1) = *((D*)pdb0) // D& operator=(D&) is invoked.

Can we invoke D& operator=(D&) without explicit casting?  Even if I define
B& operator=(B&) as a virtual function, this cannot be done because of the
strong type checking, i.e., D& operator=(D&) cannot be binded to virtual B&
operator=(B&).   Am I asking too much?

Regards,



-- 
Naoki Saito (saito@sdr.slb.com)
Schlumberger-Doll Research