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From: johnson@p.cs.uiuc.edu
Newsgroups: comp.object
Subject: Re: "Messaging" (Re: Reentrant code)
Message-ID: <135300010@p.cs.uiuc.edu>
Date: 17 Oct 89 16:40:36 GMT
References: <8636@goofy.megatest.UUCP>
Lines: 29
Nf-ID: #R:goofy.megatest.UUCP:8636:p.cs.uiuc.edu:135300010:000:1277
Nf-From: p.cs.uiuc.edu!johnson    Oct 16 17:51:00 1989



I said
>> There is no essential difference between Smalltalk messages and C++
>> virtual functions.

psrc@pegasus.ATT.COM said
>Well, not really.  
and mentioned perform:.

I've used Smalltalk heavily for the last four years, and C++ off
and on for the last three years.  I still say that there is no
practical difference between messages and virtual functions.  One
exotic application for perform: is in a distributed Smalltalk that 
we built, where a message to a proxy object on one machine would
cause a string to be sent to another machine.  The string was parsed
and turned into a symbol, which was used to "perform:" the operation
on the remote object.  However, RPC systems do something similar using
numbers instead of symbols, so there is no real loss of power.

The big advantage of Smalltalk untyped messaging is that it is much
better suited to experimental programming.  Virtual functions are
closely tied to C++'s type system, which forces the programmer to
decide interfaces early.  When the interfaces turn out to be wrong,
as usually happens, the programmer has to make lots of revisions.
However, from a high-level design point of view, I don't think that
there is much difference between them.

Ralph Johnson -- University of Illinois at Urbana-Champaign