gistfile1.txt

[1] pry(main)> module Behavior
[1] pry(main)*   extend ActiveSupport::Concern
[1] pry(main)*
[1] pry(main)*   included do
[1] pry(main)*     add(1)
[1] pry(main)*   end
[1] pry(main)*
[1] pry(main)*   class_methods do
[1] pry(main)*     def add(value)
[1] pry(main)*       @value = value
[1] pry(main)*     end
[1] pry(main)*   end
[1] pry(main)* end
=> :add
[2] pry(main)>
[3] pry(main)> class Parent include Behavior; end
=> Parent
[4] pry(main)> Parent.instance_variable_get(:@value)
=> 1
[5] pry(main)>
[6] pry(main)> class Child < Parent; end
=> nil
[7] pry(main)> Child.instance_variable_get(:@value)
=> nil