From: Joel VanderWerf <vjoel@...>
Date: 2004-12-16T07:43:41+09:00
Subject: Re: Can I make a new function like attr_accessor? (solved)

James Edward Gray II wrote:
> On Dec 15, 2004, at 4:28 PM, Jack, Paul wrote:
> 
>> The Observable pattern that itsme213 recommended doesn't
>> seem to fit my needs since I need multiple listeners per
>> emitter but maybe that's just Java think...
> 
> 
> Observable does support multiple listeners, just FYI.
> 
> James Edward Gray II
> 

If he's talking about standard ruby Observable, then yes it does support 
multiple listeners.

If he's talking about my inaptly named Observable module (shoulda been 
ObservableAttrs) then the answer is more subtle.

You can have multiple listeners, as long as the listeners are distinct 
object, rather than multiple listener clauses for one object. In fact, 
multiple listener clauses for an object are perfectly fine too, as long 
as they are listening for distinct patterns. The following example has 
two listeners, each with two "when" clauses:

   require 'observable'

   class Speaker
     extend Observable
     observable :foo
     def run
       self.foo = "1"
       self.foo = "2"
       self.foo = "3"
     end
   end

   class Listener
     def initialize(speaker)
       speaker.when_foo /2/ do |v|
         puts "saw a 2 in #{v.inspect}"
       end
       speaker.when_foo /\d/ do |v|
         puts "saw a digit in #{v.inspect}"
       end
       # This would override the first when_foo clause
       #speaker.when_foo /2/ do |v|
       #  puts "overridden"
       #end
     end
   end

   spk = Speaker.new
   lst = [Listener.new(spk), Listener.new(spk)]

   spk.run

OUTPUT

saw a digit in "1"
saw a digit in "1"
saw a 2 in "2"
saw a digit in "2"
saw a digit in "2"
saw a 2 in "2"
saw a digit in "3"
saw a digit in "3"