<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1">
<title></title>
</head>
<body>
I'll grant all those arguments -- I'm just showing my LISP and PERL
experiences, where it's you're only choice in one, and more convenient
in the other (gotta love that "( $fee, $fie, $foe ) = &fum();"
syntax in PERL :-)).<br>
<br>
Boris Gaertner wrote:<br>
<blockquote type="cite"
cite="mid006901c31007$83196180$360807d5@Standard">
<meta content="text/html; charset=iso-8859-1"
http-equiv="Content-Type">
<meta content="MSHTML 5.00.2614.3500" name="GENERATOR">
<style></style>
<div> </div>
<div>Ingo Hohmann <<a href="mailto:ingo@2b1.de">ingo@2b1.de</a>>
asked about ways to represent</div>
<div>multiply return values and he got some interesting answers.</div>
<div> </div>
<div>I agree with Cees that code like</div>
<div> </div>
<div>result := foo doSomething.<br>
(bar := result at: 1) > 0<br>
ifTrue: [self error: (result at: 3)]<br>
ifFalse: [^result at: 2]<br>
</div>
<div>is a candidate for easy improvements. Yes, it is of course
possible to use an Array and it works, but </div>
<div> </div>
<ul>
<li>when you use a class - say: MyStructuredMessage - you can use
the option "class refs" of the browser to find all methods that
reference the class. You can of course also ask for all references
to class Array, but in our newest standard image the browser will
disappoint you with almost 2.000 methods. It is then your task to
find out what all these methods do and which are the ones that you
are looking for. </li>
<li>when you use methods with specific names, you can search for
both the senders and the implementors. This is often very helpful.
You can of course search for all senders of method 'at:' but you
have to know that this method is defined in the instance protocol of
Object (and inherited by Array) and you will get more the 3.500
senders (in out standard image) </li>
<li>as Cees pointed out, method names are much more informative
than array indices. Users of your code will find it easier to read
'result payload' 'result status' 'result checksum' than (result at:
1), (result at: 2) and so on. You should also not underestimate the
possibility that you want to change the format of you structured
return value for some reason. Consider the following situation:
<ul>
<li>You have a value <strong>Array with: payload with:
checksum with: state</strong> </li>
<li>Somewhere in your code you access the state with (array at:
3), in other places you write (array last) </li>
<li>You did not anticipate it, but for some reason you have to
add a fourth data field to your value. To keep the expression
(array last) correct, you cannot add the new field after the last
one, and to keep the expression (array at: 3) correct, you have to
add the new field after the third field which is the last one. You
have now all reason to rethink your use of an array.</li>
</ul>
</li>
</ul>
<div>There is a related problem and I want to explain that too,
because it is one of the most costly mistakes that I ever made (in
Smalltalk, not in life)</div>
<div> </div>
<div>I had a lot of cooperating classes and in the instance protocol
of all these classes I had methods with identical names (I wanted to
use polymorphism and that was ok). Initially these methods had a small
number of parameters, but later I had repeatedly to add additional
parameters. Every time I needed a new parameter, I added that new
parameter to all these methods and than I updated all senders. Finally
I removed all the obsoleted methods. I can only regret my foolishness,
but it took me some time to understand that I failed to define a class
for all my parameters. (I was even not smart enough to use an array!)
Now that I have understood that, the introduction of an additional
parameter is very easy. I add an instance variable and access methods to
the class that keeps all the parameters and I have to rework only the
methods that have to access the additional parameter.</div>
<div> </div>
<div>Given this experience, I think now that is is not best practice
to ask "Do I really need a class?". It is - in my opinion - much
better to ask: "What problems will I incur when I do not define a
class?"</div>
<div> </div>
<div>By the way, I agree that the use of exception is not always a
good solution. Use of exceptions becomes increasingly difficult when
you have to handle additional data elements (the equivalent of adding
instance variables to a class)</div>
<div> </div>
<div>Just my 2 eurocents,</div>
<div>Boris</div>
<pre wrap="">
<hr width="90%" size="4">
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="80">--
.. Donald Major "Tech Support..your Windows machine doesn't
dtm SAS Institute Inc. work? Have you tried installing a Macintosh?"
Cary, NC 27513 - me SAS - "The Power to Know"
AKA "Ol' Baby Lee"
</pre>
</body>
</html>