gistfile1.rb

module B
  attr_accessor :b_config

  def get_b_config
    @config[:b]
  end

  def B.extend_object(target)
    super
    target.b_config = target.get_b_config
  end
end

class A
  def initialize
    @config = {:a => 1, :b => 2}
    self.extend B
  end
end

A.new.b_config.should eq 2