From: Charles Oliver Nutter <charles.nutter@...>
Date: 2007-10-28T15:34:44+09:00
Subject: Re: How fast does your Ruby run?

Joel VanderWerf wrote:
> The dependence on ObjectSpace is kind of nasty, isn't it? A library 
> shouldn't use ObjectSpace in this way, because what it finds there may 
> depend on whether GC has run recently or not.

Yes, ObjectSpace is a useful tool for walking the heap when you really 
want to, but it's not deterministic about whether or when it will find 
the object(s) you want. So I agree it's a bad feature to use as part of 
libraries you want to work the same way every time.

In the case of test/unit, most TestCase descendants get hard-referenced 
as classes assigned to constants somewhere. However if you constructed a 
test case as follows:

Class.new(Test::Unit::TestCase) { def test_something; end }

...it may or may not run with the default loader.

> Good to hear you found a way to support it anyway, though.
> 
> Does your mechanism to walk child classes prevent them from being 
> collected, if there are no other references to them? If so, then it 
> isn't quite bug-compatible (though it is unlikely to matter):

No, the references to child classes are all weak references; if they go 
away, the references will go away. It's a much smaller price to pay than 
attaching weak references to *all* constructed objects (to my knowledge, 
it costs almost nothing, and test/unit still works.

The typical way I think people would fix test/unit's use of ObjectSpace 
would be to add a Class#inherited hook that records all subclasses of 
TestCase. But nobody's gone ahead with that change yet.

- Charlie