From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-04-14T01:49:36+09:00
Subject: Re: Memoize and GC

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
irb(main):024:3* a
irb(main):025:3> end
irb(main):026:2> a
irb(main):027:2> end
irb(main):028:1> end
=> nil
irb(main):029:0> obj = A.new
=> #<A:0xb7c9ef20>
irb(main):030:0> obj.a
expensive calculation of a...
=> "complex value"
irb(main):031:0> obj.a
=> "complex value"

Jesus.