Question

In Objective C on iOS, are instance variables of object reference type (id, NSObject *, etc.) auto-initialized to nil upon object allocation or not?

Answer 1

Yes, see The Objective C Programming Language documentation on Apple’s site.

The alloc and allocWithZone: methods initialize a newly allocated object’s isa instance variable so that it points to the object’s class (the class object). All other instance variables are set to 0. Usually, an object needs to be more specifically initialized before it can be safely used.