Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!hp4nl!media03!pkr
From: pkr@media03.UUCP (Peter Kriens)
Newsgroups: comp.lang.smalltalk
Subject: Re: Access methods - New feature ?
Message-ID: <2273@media03.UUCP>
Date: 25 Apr 91 08:11:48 GMT
References: <1991Apr21.221149.8057@vuse.vanderbilt.edu> <VOSS.91Apr22113638@laslo.cs.uiuc.edu> <VOSS.91Apr22183834@laslo.cs.uiuc.edu> <1991Apr23.010026.25098@ccs.carleton.ca> <VOSS.91Apr23194435@laslo.cs.uiuc.edu>
Reply-To: pkr@media03.UUCP (Peter Kriens)
Organization: aQute, Netherlands
Lines: 30

voss@cs.uiuc.edu (Bill Voss) writes (after giving an example about point
not using x,y for calculating the distance between two points)

        Now is it ALWAYS wrong to use access methods?
        I do NOT contend that it is ALWAYS wrong.v:Soon
        I think it must be judged on a case by case basis.
        However, I do contend that it is USUALLY wrong.
 
1: I think a basic quality of object oriented design is defining a
"functionality" only in place. Calculation of the distance between 
points should therefore be placed in one location and that is the
Point class. Your example violates this first rule. I cannot in the
world see what this example has to do by accessing through a method
of the instance variable. 

2: Instance variables have a natural tendenncy to contain the most
relevant information regarding an object. So it seems quite natural
to me that they should be accessible outside the object. What I dont
want is that once I change the implementation (e.g. change a Point
from x,y to polar coordinates) that my clients break. As long as
the instance variables are accessed through methods (and i dont seen another
way to do it in Smalltalk) I can always keep the same interface. So
what is wrong in have the instance variable access methods?

3: I do not promote to make EACH instance variable automatically
accessible, but I think it would be very nice to allow variables
to be exported like in Eiffel.

Peter Kriens
pkr@media01.uucp