tiny example of ruby module usage

app.rb

module Sayable

  def self.included(host_class)
    host_class.extend ClassMethods
  end

  module ClassMethods
    def sound sound
      @the_sound = sound
    end

    def the_sound
      @the_sound
    end

  end

  def say
    puts self.class.the_sound
  end
end

class Dog
  include Sayable

  sound 'bark'
end

class Cat
  include Sayable

  sound 'meow'
end

dog = Dog.new
dog.say
# ===> 'bark'

cat = Cat.new
cat.say
# ===> 'meow'