Un pequeño ejemplo de mixins, mínimamente funcional

mixins_test.rb

module DynamicObject

  def values
    @values ||= {}
  end
  
  def method_missing(name,*args)  
    if name.to_s.end_with?('=')
      self.assign_value(name.to_s[0..-2].to_sym,args[0])
    else
      values[name]
    end
  end
 
  def assign_value(name,value)
    values[name]=value
  end
  
end

module Observable
  
  def add_listener(event, listener)
    listeners(event).push(listener)
  end
  
  def trigger(event, *args)
    listeners(event).each { |a_listener|
      a_listener.notify(event, args)
    }
  end
  
  def remove_listener(event, listener)
    listeners(event).pop(listener)
  end
  
  def __listeners
    @listeners ||= {}
  end
  
  def listeners(event) 
     __listeners[event] ||= []
  end
end


class Model
  include DynamicObject
  include Observable
  
  def assign_value(name,value)
    super
    self.trigger(name, value)
  end
  
end

require 'rspec'

class TestListener
  def initialize(output)
    @output = output
  end
      
  def notify(event, args)
    @output.push({"event"=>event, "args"=>args})
  end
end

describe 'testeando observable' do
  
  it 'observable dispara evento' do
    class Observado
      include Observable
    end
    
    a = Observado.new
    
    output = []
    
    a.add_listener("evento", TestListener.new(output))
    
    a.trigger("evento", "parametros")
    
    output.should== [{"event"=>"evento", "args"=>["parametros"]}]
    
  end
  
end

describe 'testeando modelo' do
  it 'modelo dispara evento al setear valor' do
    a = Model.new
    
    output = []
    
    a.add_listener(:saraza, TestListener.new(output))
    
    a.saraza = "sarlompa"
    
    output.should== [{"event"=>:saraza, "args"=>["sarlompa"]}]
  end
end