From: Phrogz <phrogz@...>
Date: 2007-11-23T12:20:00+09:00
Subject: Re: Class Methods from Modules

Greg Willits wrote:
> In this play code below, I want to use initialize_colors in either the
> class Shape or Square as a class method.

Including a module in a class causes instance methods of the module to
be in the lookup path for instances of the class. Extending a class
using a module causes instance methods of the module to be in the
lookup path for the class itself.

(See http://phrogz.net/RubyLibs/RubyMethodLookupFlow.png)

A common idiom to be able to cause a class to get both class and
instance methods when including a single module follows:

module Color
  module ClassMethods
    def initialize_colors
      p "woot!"
    end
  end

  def giggle
    puts "tee hee!"
  end

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

class Shape
  include Color
  initialize_colors
  #=> "woot!"
end

Shape.new.giggle
#=> "tee hee!"