Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!wuarchive!emory!att!pacbell.com!pacbell!osc!jgk
From: jgk@osc.COM (Joe Keane)
Newsgroups: comp.lang.lisp
Subject: Re: Problems Copying Structures
Summary: Object-oriented doesn't solve deep copying.
Keywords: defstruct structures copying
Message-ID: <4083@osc.COM>
Date: 13 Dec 90 20:36:50 GMT
References: <1990Dec8.071142.5318@cec1.wustl.edu> <1990Dec8.180825.21702@Think.COM> <93985@aerospace.AERO.ORG>
Reply-To: jgk@osc.COM (Joe Keane)
Organization: Versant Object Technology, Menlo Park, CA
Lines: 21

In article <1990Dec8.180825.21702@Think.COM> barmar@think.com (Barry Margolin)
writes:
>Structure copiers are only supposed to copy the structure itself, not the
>objects referenced by the structure.  They are like COPY-LIST rather than
>COPY-TREE.  If you want more, you have to write your own copier function
>that does precisely what you want.  There's no standard function that's
>able to read the programmer's mind and determine which parts of a structure
>should be copied and which should just be referenced.

>Note that this [structure copier] still only copies one level more
>than the automatically-generated copier.  If you also want to copy
>the objects referenced in the arrays you'll have to do more.

In article <93985@aerospace.AERO.ORG> srt@aerospace.aero.org (Scott "TCB"
Turner) writes:
>One of the better arguments for object-oriented programming.

I don't see what object-oriented programming has to do with this.  The same
problems with deep vs. shallow copying come up, and there's no magic solution
which always does what you want.  One thing i do know is that it's a hell of a
lot easier to automatically generate functions you want in Lisp than in C++.