This post originated from an RSS feed registered with Agile Buzz by James Robertson. Original Post: Things not to do Feed Title: Cincom Smalltalk Blog - Smalltalk with Rants Feed URL: http://www.cincomsmalltalk.com/rssBlog/rssBlogView.xml Feed Description: James Robertson comments on Cincom Smalltalk, the Smalltalk development community, and IT trends and issues in general. Latest Agile Buzz Posts Latest Agile Buzz Posts by James Robertson Latest Posts From Cincom Smalltalk Blog - Smalltalk with Rants

subclasses := self allSubclasses.

That looks inocuous enough. Trouble was, I did it in a class method. Recall that classes are instances of their Metaclass, and descend from Class (up to Behavior). Look at the instance variables for Behavior:

Smalltalk.Core defineClass: #Behavior
	superclass: #{Core.Object}
	indexedType: #none
	private: false
	instanceVariableNames: 'superclass methodDict format subclasses '
	classInstanceVariableNames: ''
	imports: ''
	category: 'Kernel-Classes'

One of them is 'subclasses'. So look again at what I did - each time through that loop, I made subclasses into a bigger collection, all filled with duplicates! When I looked at it in my development image, I had over 10,000 subclasses of the class in question! No wonder I was chewing memory, and no wonder iterating over the subclasses (that's what the code in question did) was taking a long time, and getting slower each time through!

Fixing it was a simple matter of changing the code to use a temp variable - problem solved. There's a larger lesson here though - look at Behaviior abd the subclasses down to Class. You don't want to use a variable that matches the name of any of those instance variables on the class side - referencing them in tools is ok, but assigning new values to them is a very bad idea. The only real hint you'll get is that you won't be prompted to declare a temp variable - but that's very, very easy to miss.

I'm looking at adding a code critic rule to flag these issues - if I get that working, I'll post an update. In the meantime, watch out for this sort of thing if you start seeing oddball behavior in an image.