From: Joshua Ballanco <jballanc@...>
Date: 2007-06-07T14:47:17+09:00
Subject: KVO in Ruby

Hey all!

I'm still relatively new to Ruby, so forgive me if this seems like a
naive (or even stupid) question, but...

Is there a good method for implementing Key-Value Observing in Ruby?

Basically, what I'd like to be able to do is this:

class Actor
  attr_accessor :var_to_change

  def change_var
    @var_to_change = 1
    100.times {@var_to_change += 1}
  end
end

class Observer
  def initialize(act)
    @actor = act
    act.add_observer(self, var_to_change)
  end

  def observeValue(var, sender)
    if sender == @actor
      puts "The value is now #{var}"
    end
  end
end

act = Actor.new
obs = Observer.new(act)
thr = Thread.new {act.change_var}
thr.join

The resulting output would be:
The value is now 1
The value is now 2
...and so on.

I realize that there are all sorts of ways that similar functionality
could be achieved, but something about KVO is really attractive
(especially since Ruby is already really good at KVC). It seems to me
that this would be a fairly easy to implement as a module, but I don't
want to have to do the work if someone else already has. Does anyone
know how RubyCocoa handles KVO? or if it does?

Thanks for any help/comments/scornful rebukes. ;-)

-Josh

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