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From: dawg6844@uxa.cso.uiuc.edu (Dan Walkowski)
Newsgroups: comp.lang.smalltalk
Subject: Re: To Subclass or Encapsulate? (WAS: Access Methods)
Message-ID: <1991Apr24.213502.18364@ux1.cso.uiuc.edu>
Date: 24 Apr 91 21:35:02 GMT
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mjohnson@cosmos.acs.calpoly.edu (Mark S. Johnson) writes:
>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-


These questions are most definitely not too naive for this group.  These are
important questions, which unfortunately do not have easy answers.  Once again,
it depends on the exact situation.  In other words, what are you going to DO
with your vectors once you have them?  Depending on the answer to that question,
I could make arguments for either answer (1), (2), or (3).  
For example, if you are going to do lots of 'array-like' stuff with your 
vectors, like moving, sorting, and otherwise diddling with individual elements,
then I would probably argue for case number (1).  If, however, you want to
think of your vectors more like 'whole' objects, instead of a collection of
elements, (or if a vector 'contains' other information besides its elements, for
example: a length?  a color?  who knows?)  then I would personally choose
implementation (2).  And, lastly, if the 'main' thing you wish to do with your
vectors were something completely different, say plot them in different colors,
then perhaps it should be subclassed from some graphics object. (?)
Believe me, I almost ALWAYS spend more time deciding how to structure my problem
than actually writing the code.  Why?  Because it makes the code cleaner and
easier to write, and easier to change later.

dan

--
_______________________________________________________________________________
Dan Walkowski                          | To understand recursion, 
Univ. of Illinois, Dept. of Comp. Sci. |   you must first understand recursion.
walkowsk@cs.uiuc.edu                   |