extending with ModA
this is method bar of ModB
extending with ModB
this is method bar of ModB

module ModA
  extend ActiveSupport::Concern

  module ClassMethods
    def bar
      puts "this is method bar of ModA"
    end

    # grab UnboundMethod of ModA::ClassMethods::bar
    a_bar = instance_method(:bar)

    # using define_method to capture a_bar
    define_method :extend_with_mod_a do
      puts "extending #{self} with ModA"
      # invoke ModA::ClassMethods::bar properly bound to the class being extended/included with ModA
      a_bar.bind(self).call
    end
  end
end

ActiveRecord::Base.send :prepend, ExtModule