Path: utzoo!attcan!uunet!dalcs!aucs!831059l
From: 831059l@aucs.UUCP (Langlois)
Newsgroups: comp.lang.smalltalk
Subject: Re: Differencs between Smalltalk/V and Smalltalk/V286
Message-ID: <1440@aucs.UUCP>
Date: 10 Dec 88 02:47:42 GMT
References: <1424@aucs.UUCP> <1428@aucs.UUCP>
Reply-To: 831059l@aucs.UUCP (Langlois)
Organization: School of Computer Science, Acadia Univ., Nova Scotia
Lines: 33


	Here is an interesting problem. I wanted to create a class Queue
as a subclass of class SortedCollection. An instance of class Queue would
have the sortBlock [ :a : b | a < b ] plus some instance variables such
as observations (to keep track of the number of objects which entered the 
queue), maxLength (the maximum length of the queue), etc. 

	To create a new Queue, I tried the following method:

new
    ^(self sortBlock: [ :a :b | a < b]) initialize

I then execute the following:

|aQueue|
aQueue := Queue new

I very quickly get a walkback, with the label "stack overflow". I tried this
in Smalltalk/V and it worked fine, in Smalltalk/V286, a different story.
I thought using a selector other than new might help so I tried newQueue, but
not luck. I got the same error. 

It took a long time but I finally found the solution to the problem. I defined
class Queue as a variableSubclass of class SortedCollection. That is why (?)
I got the overflow. Just on a whim, I decided to try to define it as a subclass
instead and it worked. In Smalltalk/V, SortedCollection is a variableSubclass
of OrderedCollection. In Smalltalk/V286, it is a subclass of OrderedCollection.
Take a guess at whether it was documented as a change from V to V286!!!

Steven Langlois     UUCP:     {uunet|watmath|utai|garfield}!dalcs!aucs!831059l
Acadia University   BITNET:   Steven@Acadia
Wolfville, NS       Internet: Steven%Acadia.BITNET@CUNYVM.CUNY.EDU
CANADA  B0P 1X0