fun_with_modules.rb

require "rubygems"
require "colorize"

def desc(msg)
  puts "Description".colorize(:yellow)
  puts "===========".colorize(:yellow)
  puts msg.colorize(:white)
end

def example(body)
  puts "\nRunning:".colorize(:yellow)
  body.each_line do |line|
    puts "  #{line}"
  end
  result = eval(body)
  puts "Success! Result is #{result.inspect}".colorize(:green)
rescue Exception => e
  puts "Failed! Exception is #{e.class}: #{e.message}".colorize(:red)
ensure
  puts "\n"
end

desc "Including a module into a class makes it's instance methods available to the class and it's subclasses"

example <<EOR
module Groot
  def groot
    "I am groot"
  end
end

class A
  include Groot
end

A.groot
EOR

example <<EOR
module Groot
  def groot
    "I am groot"
  end
end

class A
  include Groot
end

A.new.groot
EOR

example <<EOR
module Groot
  def groot
    "I am groot"
  end
end

class A
  include Groot
end

class B < A
end

B.new.groot
EOR

desc "Extending a module onto a class makes it's instance methods available as class methods"

example <<EOR
module Groot
  def groot
    "I am groot"
  end
end

class A
  extend Groot
end

A.groot
EOR

example <<EOR
module Groot
  def groot
    "I am groot"
  end
end

class A
  extend Groot
end

A.new.groot
EOR

desc "You can't call `include` on a class instance, but can call `extend`"

example <<EOR
module Groot
  def groot
    "I am groot"
  end
end

class A
end

A.new.include(Groot).groot
EOR

example <<EOR
module Groot
  def groot
    "I am groot"
  end
end

class A
end

A.new.extend(Groot).groot
EOR

desc "included modules are added between a class and it's superclass in the ancestor chain"

example <<EOR
class SuperClass
end

module ExampleModule
end

class SubClass < SuperClass
  include ExampleModule
end

SubClass.ancestors
EOR

desc "prepended modules are added **before** a class in the ancestor chain"

example <<EOR
class SuperClass
end

module ExampleModule
end

class PrependedSubClass < SuperClass
  prepend ExampleModule
end

PrependedSubClass.ancestors
EOR

desc "extended modules are not added to the classes ancestor chain (google \"Ruby Eigenclass\" if you want to know where they go)"

example <<EOR
class SuperClass
end

module ExampleModule
end

class ExtendedSubClass < SuperClass
  extend ExampleModule
end

ExtendedSubClass.ancestors
EOR