Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ames!pacbell!att!dptg!pegasus!psrc
From: psrc@pegasus.ATT.COM (Paul S. R. Chisholm)
Newsgroups: comp.object
Subject: Re: "Messaging" (Re: Reentrant code)
Summary: Smalltalk messages vs. C++ virtual messages
Message-ID: <4171@pegasus.ATT.COM>
Date: 16 Oct 89 00:35:06 GMT
References: <8636@goofy.megatest.UUCP> <135300001@p.cs.uiuc.edu>
Organization: AT&T Bell Laboratories
Lines: 25

In article <135300001@p.cs.uiuc.edu>, johnson@p.cs.uiuc.edu writes:
> There is no essential difference between Smalltalk messages and C++
> virtual functions.

Well, not really.  If you know (at run time) the name of a Smalltalk
message (at compile time), you can arrange to send that message to an
object.  For example, I can say:
	obj perform: ( 'new' asSymbol )
More to the point, instead of using a String constant, I could have
prompted the user for the name of a message to send.  If the message
doesn't exist, or takes the wrong number of arguments, you'll get a
walkback and/or a debugger.

That information is completely lost by run time in C++ programs.  (On
the other hand, C++ programs don't usually run in an environment where
they can ask the user for help.)

This is neither a general strength nor limitation of either language.
The abilities reflect the intended use of the languages.

> Ralph Johnson

Paul S. R. Chisholm, AT&T Bell Laboratories
att!pegasus!psrc, psrc@pegasus.att.com, AT&T Mail !psrchisholm
I'm not speaking for the company, I'm just speaking my mind.