[ruby-talk:8578] Re: Observing multiple observables

Hi,

From: Kevin Smith <[e-mail]>

> But I just ran into a case where I wanted to 
> observe two things at the same time. I solved it 
> by creating a little observable proxy class, but 
> I think the library could be tweaked to provide 
> the same  functionality while retaining backward 
> compatibility.

I had used similar extention to Obserbable.  Because my implementation
was just to fill the needs at hand, I did not even bother to modify
observer.rb, though.  I just added following 7 lines of code in my
app.

module Observable
  def add_callback(callback)
    @observer_peers = [] unless defined? @observer_peers
    callback.instance_eval %{alias update call}
    @observer_peers.push callback
  end
end

Then an Observer looks like...

class TwoHeadedObserver
  def initialize(foo, bar)
    @foo, @bar = foo, bar
    @foo.add_callback(method :look_at_foo)
    @bar.add_callback(method :look_at_bar)
  end

  ....
end

Main difference to your version (beside the interfacce) is that it
holds references to methodd ojbects rather than generating them for
each 'update' call.  You may also concider this because it is more
efficient (unless you have specific needs to redefine the call back
method at runtime...).

Regards,
Kenichi, Komiya.