Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!petunia!news
From: mjohnson@cosmos.acs.calpoly.edu (Mark S. Johnson)
Newsgroups: comp.lang.smalltalk
Subject: To Subclass or Encapsulate? (WAS: Access Methods)
Message-ID: <2815b936.c65@petunia.CalPoly.EDU>
Date: 24 Apr 91 16:58:30 GMT
Distribution: usa
Organization: Mechanical Engrg. Dept., California Poly. State U., SLO
Lines: 43




I've read the access method discussion here with great interest and as
a novice Smalltalker I have learned a lot. I'd like to thank Bill Voss
for his extended answer to my "eyeColor" question. I think in some
vague way that I already knew the answer but was having difficulty
putting it into words. The bottom line for me: any objects that I
build should be much more powerful and much more "active" than mere
"records;" avoiding access methods will help remind me of this.

I have a related style question. (The reason I have these "style"
questions is that I believe that I will be slowly "growing" a series
of applications in my meager spare time; therefore, "style" as it
relates to the ease of maintaining and extending programs is important
to me.)

THE QUESTION:

Say I would like to add a Vector class for mathematical calculations.
I could:

   (1)   create Vector as a subclass of Array and modify/add methods
         (e.g., methods to insure that the elements of a Vector were
         only Numbers, vector multiplication methods, etc)
-OR-
         
   (2)   create Vector as a subclass of Object and "encapsulate" an
         Array inside Vector as an instance variable. That way I could
         more easily protect the underlying Array from messages that I
         don't want it to receive.
-OR-

   (3)   ???

If these questions are too naive for this group please let me know and
I'll just shut up and listen/read.

Thanks to all,
Mark

-- 
Mark S. Johnson        mjohnson@stn9.me.calpoly.edu      (129.65.19.9)