Alan Kay and Missing Messages
I think there&#x27;s a big difference between not understanding the message, and not understanding the data (a message parameter).<p>When they get an unrecognized message, Objective C objects call their doesNotRecognizeSelector method, and Smalltalk objects call their doesNotUnderstand method.<p>And the object sending the message can first check with respondsToSelector in Objective C or respondsTo in Smalltalk, before sending the message.<p>But validating and sanitizing input parameters is a totally different thing than handling unknown messages, orthogonal to object oriented programming.