an_intro.textile

If one was inclined to use the acts_as_yaffle pattern, they would probably use the second one, rather than the heavily cargo-culted first one.

first.rb

module Yaffle
  def self.included(base)
    base.send :extend, ClassMethods
  end

  module ClassMethods
    def acts_as_yaffle(options = {})
      cattr_accessor :yaffle_text_field
      self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
      send :include, InstanceMethods
    end
  end

  module InstanceMethods
    def squawk(string)
      write_attribute(self.class.yaffle_text_field, string.to_squawk)
    end
  end
end

ActiveRecord::Base.send :include, Yaffle

second.rb

module Yaffle
  def acts_as_yaffle(options = {})
    cattr_accessor :yaffle_text_field
    self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
    include InstanceMethods
  end

  module InstanceMethods
    def squawk(string)
      write_attribute(self.class.yaffle_text_field, string.to_squawk)
    end
  end
end

ActiveRecord::Base.extend(Yaffle)

the_code_annotated.rb

module Yaffle
  # since this is for internal consumption only, just extend directly;
  # don't rewrite the include method to mean extend
  def self.included(base)
    # extend is a public method
    base.send :extend, ClassMethods
  end

  # if we extended directly, we could get rid of the ClassMethods
  # module and move the methods into the Yaffle module. You onluy
  # ever need one of ClassMethods or InstanceMethods
  module ClassMethods
    def acts_as_yaffle(options = {})
      cattr_accessor :yaffle_text_field
      self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s

      # we're inside the class, so we don't need to use send to
      # use a private method
      send :include, InstanceMethods
    end
  end

  module InstanceMethods
    def squawk(string)
      write_attribute(self.class.yaffle_text_field, string.to_squawk)
    end
  end
end

# If we'd used extend, we wouldn't need a send
ActiveRecord::Base.send :include, Yaffle