Why doesn't the Objective-c runtime set dealloc'd object instances to nil?

Question

Sometimes I set objects to nil after releasing them to avoid crashes due to unexpected messages sent to dealloc'd objects.

Why doesn't the Objective-c runtime do this automatically when an object is finally dealloc'd?

Answer 1

Because pointers are passed by value and not reference. All dealloc gets is a local copy of the pointer; any changes it makes are discarded. Same goes for C's free and C++'s delete.