include_class_instance.rb

# source: http://blacklane.github.io/2016/04/23/lessons-learned-from-some-of-the-best-ruby-codebases-part-1/

class Foo < Module

  def initialize
    @module = Module.new
  end

  def included(descendant)
    @module.class_eval do

      def b
        "B"
      end

    end

    descendant.send(:include, @module)
  end

end

# class Bar
#   include Foo
# end
# TypeError: wrong argument type Class (expected Module)
# from (pry):2:in `include'
# [3] pry(main)> Foo.class
# => Class


class Bar
  include Foo.new
end

puts Bar.new.b