Subject: Re: Deep copy in lisp: how?
From: (Rob Warnock)
Date: 2000/04/15
Newsgroups: comp.lang.lisp
Message-ID: <8d8e2b$17i6$>
Joerg-Cyril Hoehle <> wrote:
| Kent M. Pitman article
| about why there can't be an all general copy...
| I sincerely hope that by now, you read both this and Tim Bradshaw's
| article at

One of the examples in Tim's paper was very telling -- a "queue" object
which contains pointers to *shared* sub-structure. If one had *any*
lingering doubts about the impossibility of a "universal" or "generic"
copy doing the right thing, that example would surely blow them away.

Objects may have *application*-defined internal consistency invariants
which are destroyed by copying, and a general copy operator *can't* know
(in general) how to preserve (or at least, restore) those invariants
through the copying process.


Rob Warnock, 41L-955
Applied Networking
Silicon Graphics, Inc.		Phone: 650-933-1673
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