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From: pallas@Neon.Stanford.EDU (Joe Pallas)
Newsgroups: comp.lang.lisp
Subject: Re: CLOS: is it OOP?
Message-ID: <11815@polya.Stanford.EDU>
Date: 15 Sep 89 23:47:47 GMT
References: <19582@mimsy.UUCP> <29564@news.Think.COM>
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In article <29564@news.Think.COM> barmar@think.COM (Barry Margolin) writes:

>I'm also a fan of encapsulation and protection, but I don't think that
>they are absolutely required for an object system.  CLOS probably
>lacks them mostly because Flavors lacks them, and Flavors probably was
>copying DEFSTRUCT-style inheritance.

and

>The distinction between generic functions and active data is mostly
>syntactic.  Can you really see any semantic difference between

>	(send object 'foo ...)
>and
>	(foo object ...)

I'm inclined to agree that protection is not absolutely required for
an object-oriented language (although I wouldn't want to use one
without it).  But I would argue that it is precisely because of
generic functions that CLOS CANNOT have protection.  To have
protection, you must have a clearly defined protection boundary.
Method invocations establish such a boundary, but generic functions do
not.

>The major benefit of generic functions is that it is like the rest of
>Lisp.  You can pass them around wherever ordinary functions are
>permitted.  For instance, they can be passed to mapping functions.  In
>a message-sending system, programs that accept messages generally
>don't accept functions and vice-versa; you end up writing
>	#'(lambda (x) (send x 'foo))
>alot.

I can't say for sure, but I don't think this is true unless you spend
a lot of time writing named helper functions in CommonLisp.  I just
scanned through my Smalltalk sources and couldn't find any such
trivial lambda expressions (blocks, in Smalltalk parlance).  You
almost always want to do more than just send a simple message in such
a case.  So you either have to write a special purpose method/generic
function, or you use a lambda expression anyway.

joe