[Newbies] Re: Proper object removal

Klaus D. Witzel klaus.witzel at cobss.com
Wed Jun 4 12:41:08 UTC 2008

On Wed, 04 Jun 2008 12:12:59 +0200, Bert Freudenberg wrote:

> On 04.06.2008, at 10:32, Klaus D. Witzel wrote:
>> On Wed, 04 Jun 2008 09:55:11 +0200, Norbert Hartl wrote:
>>> The objects are still referenced in the collection you get
>>> from self selected. The line with "each := nil" is useless
>>> as each is only a temporary variable.
>> Not 100% useless, since temporary variables (and arguments, for that  
>> matter) survive any attempt, from within the same method, to garbage  
>> collect them:
>> {'this ', 'and ', 'that'} collect: [:each | ].
>> Smalltalk garbageCollect.
>> {thisContext tempAt: 1} inspect
>> first line: create some object and make a temp var point to it.
>> second line: invoke GC.
>> third line: see what's still pointed to by the temp var.
> Yikes. Klaus, please keep the hair-splitting to squeak-dev if possible.

Ah. Didn't know that enumerating+removing with a block with argument  
+ GC'ing in the same method, belongs to hair-splitting. Instead, I always  
thought that's one of the reasons that at least one to-be-removed object  
is guaranteed to not go away.

But anyways, thanks for letting me know ;)

> Assigning to a block parameter is just wrong.

You better read before you write (the way you most often do indeed ;) then  
you'd find that I didn't write any assignment to anything. Instead, I  
ignored that and pointed to a potential beginner's problem. Sorry you  
didn't like that ;)

> Setting temps to nil is unnecessary in any normal method. If your code  
> actually needs to worry about this, then you left the beginner  
> playground.

And if he does removal+GC+check for success in the same method? I cannot  
see whether someone just copies arbitrary statements given in a response  
to a question, or carefully puts them into separate methods, in his code  
in his .image, now or never ;)

> Rob: Here's a recipe to find out what is keeping your instances from  
> being garbage-collected:
> http://wiki.squeak.org/squeak/2631
> - Bert -

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