Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!odi!dlw
From: dlw@odi.com (Dan Weinreb)
Newsgroups: comp.lang.lisp
Subject: Re: CLOS: is it OOP?
Message-ID: <1989Sep15.221310.21012@odi.com>
Date: 15 Sep 89 22:13:10 GMT
References: <19582@mimsy.UUCP>
Reply-To: dlw@odi.com
Distribution: usa
Organization: Object Design, Inc.
Lines: 29
In-reply-to: folta@tove.umd.edu's message of 14 Sep 89 00:21:12 GMT

In article <19582@mimsy.UUCP> folta@tove.umd.edu (Wayne Folta) writes:

   "Because CLOS makes no effort at protection or encapsulation, some might
   find that it lacks the most essential thing for an object-oriented system."

This overstates the case.  CLOS, following Lisp philosophy, relies on
programmers to follow conventions, rather than actually imposing
access control; this is particularly helpful in interactive debugging.
In CLOS you can still say whether you want accessor functions or not
for each slot.

   "generic functions are a step away from the concept of active data and back
   toward the conventional division between passive data and active process."

This is nonsense.  The author of your book cannot distinguish syntax
from semantics, or at least worries too much about syntax.  CLOS
supports "active data" every bit as much as Smalltalk-80 does.  Even
though the character string "send" isn't used, exactly the same thing
is going on (except that CLOS is more general, having multimethods).
CLOS uses the syntax of function calling in order to fit into Lisp
better.

(Historical note: The first implementation of Flavors, 1981-1986 or
so, did use "send".  After many years of heavy experience, we found
that it would make a lot of things easier, clearer, and more elegant
to drop the "send" and use the syntax of function calls to perform
"message sending"/ "generic functions"/"virtual functions".  New
Flavors did this.  CommonLoops did the same thing, and it was retained
in CLOS.)