module X
  def x
    "x"
  end
  module_function :x

  def self.included(base)
    base.class_eval do
      public :x
    end
  end
end

class TestDefault
  include X
end

puts TestDefault.new.x
# => x



module OverwriteX
  include X
  def x
    "#{super}2"
  end
end

class TestOverwrite
  include OverwriteX
end

puts TestOverwrite.new.x
# => x



module DontOverwriteX
  include X
end

class TestDontOverwrite
  include DontOverwriteX
end

puts TestDontOverwrite.new.x
# => x