def test_adding_methods    res = "I'm a mutant-to-be String"    res2= "I'm a not-to-mute String"    puts "1: #{res}"    def res.say_hello(num)      #This method is only defined for 'res' object     return "#{self} -- #{num*3}!!!"   end   puts "2: #{res.say_hello(4)}"   # Just to make it clear:   # 'res2' did NOT get the newly created method!   begin     puts "3: #{res2}"     puts "Another String: #{res2.say_hello(4)}"   rescue     puts "I failed, because this method does not exist!"   end end