From: Robert Klemme <shortcutter@...>
Date: 2010-04-14T01:50:06+09:00
Subject: Re: Memoize and GC

On 04/13/2010 06:26 PM, Intransition wrote:
> I have a quick question. I just re-read:
> 
>   http://www.engineyard.com/blog/2010/memoization-and-id2ref/
> 
> I am wondering about garbage collection. Am I right to think that
> using
> 
>   def foo
>     @foo ||= something
>   end
> 
> will mean that @foo be GC'd when the object is GC'd, but if I do
> 
>   FOO = []
> 
>   def foo
>     FOO[object_id] ||= something
>   end
> 
> Then the memorized entry will just hang around forever?
> 
> If so, then how do we do it without polluting the instance var space
> (as in example 2), but still get the garbage collection (as in example
> 1)?

I would live with polluting the instance var space.  Btw, I usually do 
not use memoize but rather an explicit Hash with default_proc.  That way 
I have control over where I place the Hash and hence how long it lives.

Of course you can hack something together using #object_id and an 
external Hash but then you also need to create a finalizer and soon 
things get overly complicated.  If you have issues with polluting the 
instance variable namespace you can a) put all memoize containers into a 
single instance variable (typically a Hash) and / or b) generate 
instance variable names which are likely to be conflict free.

Kind regards

	robert

-- 
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