Question

I want to redefine smalltalk’s nil to work like the one in objective-c. So when nil receives a message that it can’t handle, it returns nil. Now I know that nil is just a shortcut for UndefinedObject but is there anything like method_missing in Ruby so I can redefine it in UndefinedObject to always return nil?

Answer 1

The method you are looking for is called doesNotUnderstand: in Smalltalk. You can indeed implement:

UndefinedObject>>doesNotUnderstand: aMessage
    ^ nil

However, keep in mind that this affects the complete system and might have subtle side effects or introduce bugs in other parts of the system.

Also note that UndefinedObject is not a primitive type, but a normal class inheriting from Object. Therefor nil already understands a large number of messages and might not behave as you would expect coming from Objective-C.