From: Robert Dober <robert.dober@...>
Date: 2010-04-14T21:38:47+09:00
Subject: Re: Memoize and GC

2010/4/13 Jesús Gabriel y Galán <jgabrielygalan@gmail.com>:
> On Tue, Apr 13, 2010 at 6:26 PM, Intransition <transfire@gmail.com> 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)?
>>
>> Thanks.
>>
>>
>
> One way could be using a closure that redefines the method:
>
> irb(main):019:0> class A
> irb(main):020:1> def a
> irb(main):021:2> puts "expensive calculation of a..."
> irb(main):022:2> a = "complex value"
> irb(main):023:2> self.class.send(:define_method, :a) do
I like the closure idea, but I guess the memozing got lost a little bit ;).
thus I would write
def a
 _a = nil
  self.class.module_eval do
     define_method :a do _a ||=  "expensive calculation" end
     define_method :_invalidate_a do _a = nil end
  end
  a
end
Cheers
R.

-- 
Learning without thought is labor lost; thought without learning is perilous.”
--- Confucius