Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!rutgers!mcnc!thorin!unc!barkley
From: barkley@unc.cs.unc.edu (Matthew Barkley)
Newsgroups: comp.lang.smalltalk
Subject: Re: Duplication of instance variables in subclasses
Summary: Static versus dynamic
Message-ID: <5818@thorin.cs.unc.edu>
Date: 10 Dec 88 22:19:12 GMT
References: <1397@aucs.UUCP>
Sender: news@thorin.cs.unc.edu
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In article <1397@aucs.UUCP>, 831059l@aucs.UUCP (Steven Langlois) writes:
> 
> 	Is it possible to define a subclass that just adds some new methods
> (and possibly some new instance variable of its own) to its superClass but 
> does not duplicate the instance variables of the superClass so that the new
> methods access the superClass variables and not the subClass's inheritance of 
> the variable?

I have had similar problems with Smalltalk.  They seem to come from the mis-
conception that an instance of a class has anything at all to do with an in-
stance of its superclass.  In your example, one may have dozens of Entity
instances (the class) and NO Simulation instances (the superclass).  If I
understand correctly, inheritance is static.  That is, a class inherits all
the function of the hierarchy above it, including variable names, but none
of the *values* of the variables.

I have posted this reply instead of e-mailing it because it may be wrong;
if so, someone please post or mail a correction.

Matt Barkley                               barkley@unc.cs.unc.edu
Any opinions expressed are not necessarily shared by anyone else, and may 
not even be my own. How an organization can have an opinion is beyond me.