Module, class and a default instance

moo.rb

#!/usr/bin/env ruby

# Attempt to make a module with methods that default to using state in
# a default instance of a class within the module, yet allow for
# specific instances of the class to be produced with their own state,
# that share these same module methods. It boils down to using the
# module method this in place of self.

module Moo
  extend self
  @@this = nil

  class C
    include Moo

    def say(*args)
      puts "This #{this} is saying: #{args}"
    end
  end

  def this
    if self.is_a? Moo::C
      self
    else
      @@this ||= C.new
    end
  end

  def bar
    this.say "self=#{self}, this: #{this}"
  end
end

if __FILE__ == $0
  Moo.bar
  Moo::C.new.bar
  Moo.bar
end