observer_pattern.rb

# example for observer in Ruby
require "observer"

class Tick
  include Observable

  def tick
    loop do
      now = Time.now
      changed
      notify_observers(now.hour, now.min, now.sec)
      sleep 1.0 - Time.now.usec / 1000000.0
    end
  end
end

class TextClock
  def update(h, m, s)
    printf "\e[8D%02d:%02d:%02d", h, m, s
    STDOUT.flush
  end
end

tick = Tick.new
tick.add_observer(TextClock.new)
tick.tick