Method and Message (from Rubytapas)

method_message.rb

class TeaClock
  attr_accessor :timer
  attr_accessor :ui

  def initialize(minutes)
    #Tie ui object
    self.ui = StdioUi.new
    #Tie timer object. Pass ui object so that the final implementation of notify (after plugins are loaded) is called
    self.timer = SleepTimer.new(minutes, ui)
    #Extend ui or timer objects
    init_plugins
  end

  def init_plugins
    @plugins = []
    ::Plugins.constants.each do |name|
      #Call Beep class to extend ui object with it's implementation of notify
      @plugins << ::Plugins.const_get(name).new(self)
    end
  end

  def start
    #call start on timer object which would be the SleepTimer in this case
    timer.start
  end
end

SleepTimer = Struct.new(:minutes, :notifier) do
  def start
    sleep minutes * 60
    notifier.notify('Tea is Ready!')
  end
end

class StdioUi
  def notify(text)
    puts text
  end
end

module Plugins
  class Beep
    def initialize(tea_clock)
      tea_clock.ui.extend(UiWithBeep)
    end

    module UiWithBeep
      def notify(*)
        puts "Beep!"
        super
      end
    end
  end
end

t = TeaClock.new(0.01).start