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From: dsr@luke.mitre.org (Douglas S. Rand)
Newsgroups: comp.lang.c++
Subject: Re: Copying objects
Keywords: Object copy constructor
Message-ID: <111895@linus.mitre.org>
Date: 27 Jun 90 13:40:05 GMT
References: <18753@well.sf.ca.us>
Sender: usenet@linus.mitre.org
Reply-To: dsr@luke.mitre.org (Douglas S. Rand)
Distribution: comp
Lines: 31

Copying objects is lots of fun.  You can consider a few problems/options.  

1)  Do subobject pointers get copied?  or do the subobjects get duplicated and
    the new pointer assigned?

2)  How do you handle method combination?  Is each class responsible for
the entire
    copy or does a child class ask its parent to copy the parent's data
(note that this
    involves the extra bookeeping of explicitly calling the parent
method (as AT&T won't
    admit that a symbol indicating 'super' is worth it).

3)  Do you really want an exact copy?  Maybe some instance vars need to
be individual 
    (like numerical identifiers).

etc. etc. etc.

In any case,  use a virtual function for each class in the hierarchy and
use a consistent
style.  You probably don't want to just duplicate the object.  This is, 
BTW,  why C++
doesn't provide a simple copy function (neither does CLOS in CommonLISP,
and I 
can't remember whether St80 does).

Douglas S. Rand 
Internet:   <dsrand@mitre.org>
Snail:	    MITRE, Burlington Road, Bedford, MA 
Disclaimer: MITRE might agree with me - then again...