refinement.rb

class Base
  A_VALUE = 2
  def foo
    raise "NOT IMPLEMENTED"
  end
end


class Sub < Base
  def foo
    return A_VALUE
  end
end

class BadSub < Base
  def foo
    return A_VALUE + 1
  end
end


module Refiner
  ::Base.descendants.each do |descendant|
    refine descendant do
      def foo
        p 'in refinement'
        old_value = super
        p "got #{old_value}"
        if old_value % 2 != 0
          raise "NOT EVEN"
        end
        return old_value
      end
    end
  end
end



using Refiner


Sub.new.foo
BadSub.new.foo