Ejemplo de módulos en Ruby. Ver post: http://manuelonsoftware.wordpress.com/?p=225

module.rb

#!/usr/bin/env ruby
# -*- encoding: utf-8 -*-

# Mostly stealed from ActiveSupport
class Module
  # Encapsulates the common pattern of:
  #
  #   alias_method :foo_without_feature, :foo
  #   alias_method :foo, :foo_with_feature
  #
  # With this, you simply do:
  #
  #   alias_method_chain :foo, :feature
  #
  # And both aliases are set up for you.
  #
  # Query and bang methods (foo?, foo!) keep the same punctuation:
  #
  #   alias_method_chain :foo?, :feature
  #
  # is equivalent to
  #
  #   alias_method :foo_without_feature?, :foo?
  #   alias_method :foo?, :foo_with_feature?
  #
  # so you can safely chain foo, foo?, and foo! with the same feature.
  def alias_method_chain(target, feature)
    # Strip out punctuation on predicates or bang methods since
    # e.g. target?_without_feature is not a valid method name.
    aliased_target, punctuation = target.to_s.sub(/([?!=])$/, ''), $1
    yield(aliased_target, punctuation) if block_given?

    with_method, without_method = "#{aliased_target}_with_#{feature}#{punctuation}", "#{aliased_target}_without_#{feature}#{punctuation}"

    alias_method without_method, target
    alias_method target, with_method

    case
      when public_method_defined?(without_method)
        public target
      when protected_method_defined?(without_method)
        protected target
      when private_method_defined?(without_method)
        private target
    end
  end

  # Allows you to make aliases for attributes, which includes
  # getter, setter, and query methods.
  #
  # Example:
  #
  #   class Content < ActiveRecord::Base
  #     # has a title attribute
  #   end
  #
  #   class Email < Content
  #     alias_attribute :subject, :title
  #   end
  #
  #   e = Email.find(1)
  #   e.title    # => "Superstars"
  #   e.subject  # => "Superstars"
  #   e.subject? # => true
  #   e.subject = "Megastars"
  #   e.title    # => "Megastars"
  def alias_attribute(new_name, old_name)
    module_eval <<-STR, __FILE__, __LINE__ + 1
      def #{new_name}; self.#{old_name}; end          # def subject; self.title; end
      def #{new_name}?; self.#{old_name}?; end        # def subject?; self.title?; end
      def #{new_name}=(v); self.#{old_name} = v; end  # def subject=(v); self.title = v; end
    STR
  end

end

switchable.rb

#!/usr/bin/env ruby
# -*- encoding: utf-8 -*-

#       switchable.rb
#
#       Copyright 2011 Manuel Vazquez Acosta <manu@pavla>
#
#       This program is free software; you can redistribute it and/or modify
#       it under the terms of the GNU General Public License as published by
#       the Free Software Foundation; either version 2 of the License, or
#       (at your option) any later version.
#
#       This program is distributed in the hope that it will be useful,
#       but WITHOUT ANY WARRANTY; without even the implied warranty of
#       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#       GNU General Public License for more details.
#
#       You should have received a copy of the GNU General Public License
#       along with this program; if not, write to the Free Software
#       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
#       MA 02110-1301, USA.
#
#

require './ext/module.rb'  # File from this gist
require 'rubygems'
require 'highline/import'

module Switchable
  def initialize(*args)
    super(*args)
    @switchable_status ||= false
  end

  def on(*args, &block)
    @switchable_status = true
  end

  def off(*args, &block)
    @switchable_status = false
  end

  def is_on?
    @switchable_status == true
  end

  def switch(*args, &block)
    if is_on?
      off(*args, &block)
    else
      on(*args, &block)
    end
  end
end

module RequireSecret
  def initialize(*args)
    super(*args)
    @secret ||= nil
    @secret = yield(:initialize_password) if block_given?
  end

  def set_secret(old_secret=nil, new_secret=nil, &block)
    old_secret ||= yield(:current_password, @secret) if block_given?
    if old_secret == @secret
      if block_given?
        @secret = new_secret || yield(:new_password, old_secret)
      else
        @secret = new_secret || @secret
      end
    end
  end

  def on_with_secret(*args, &block)
    secret = yield(:ask_for_password, @secret) if block_given?
    if secret == @secret
      on_without_secret(*args, &block)
    else
      raise "Invalid Password"
    end
  end

  def self.included(base)
    raise "This works only on Switchable objects" unless base.include? Switchable
    base.class_eval do
      alias_method_chain :on, :secret # Magic, now the method on will ask for the password
    end
  end
end

module ActAsSwitch
  def initialize
    super
    @target = yield(:connect_to_switachable) if block_given?
  end

  def switch_with_acts_as_switch &block
    @target.switch &block
    switch_without_acts_as_switch(&block) if respond_to? :switch_without_acts_as_switch
  end

  def self.included(base)
    base.class_eval do
      if base.include? Switchable
        alias_method_chain :switch, :acts_as_switch
      else
        alias_method :switch, :switch_with_acts_as_switch
      end
    end
  end
end

module Interactive
  def self.prompt(what, echo=nil)
    result = ask("You are require to type something to #{what}: ") { |console| console.echo = echo if echo }
  end

  ASK_THE_USER = Proc.new { |what|
    prompt what
  }

  ASK_A_SECRET = Proc.new { |what|
    prompt(what, '.')
  }

  ASK_THE_USER_TO_MATCH_SOMETHING = Proc.new do |what, match|
    answer = nil
    until answer == match
      answer = prompt(what, '.')
      puts "Your answer does not match the required #{what}" unless answer == match
    end
    answer
  end

  ASK_THE_USER_TO_NOT_MATCH_SOMETHING = Proc.new do |what, mismatch|
    answer = nil
    begin
      answer = prompt(what, '.')
      puts "Your answer is required not to match #{mismatch}" if answer == mismatch
    end while answer == mismatch
    answer
  end

  PRINT = Proc.new do |message|
    puts message
  end
end

class Door
  include Switchable
end

class SecretDoor
  include Switchable
  include RequireSecret

  def initialize &block
    if block_given?
      super
    else
      super &Interactive::ASK_A_SECRET
    end
  end

  # A door opens and closes
  alias_method :open, :on
  alias_method :close, :off
end

class Lever
  include Switchable
  include ActAsSwitch
end

normal_door = Door.new
secret_door = SecretDoor.new
lever1 = Lever.new { normal_door }
lever2 = Lever.new { secret_door }


lever1.switch &Interactive::ASK_THE_USER_TO_MATCH_SOMETHING
if normal_door.is_on?
  puts "Normal Door is open"
else
  puts "Normal Door is closed"
end

lever1.switch &Interactive::ASK_THE_USER_TO_MATCH_SOMETHING
if normal_door.is_on?
  puts "Normal Door is open"
else
  puts "Normal Door is closed"
end


lever2.switch &Interactive::ASK_THE_USER_TO_MATCH_SOMETHING
if secret_door.is_on?
  puts "Secret Door is open"
else
  puts "Secret Door is closed"
end

lever2.switch &Interactive::ASK_THE_USER_TO_MATCH_SOMETHING
if secret_door.is_on?
  puts "Secret Door is open"
else
  puts "Secret Door is closed"
end