class Santiago
  def method_missing(method_id, *args)
    p "method_missing"
    self.class.class_eval do   # do instead of here doc string
      def #{method_id}(*args)
        p "hello"
      end
    end                        # end of block instead of closing the string
    send(method_id, *args)
  end
end

Santiago.new.hello
Santiago.new.hello
Santiago.new.hello