Instance variables declared in ObjC implementation file

Question

I was watching the WWDC ARC introduction video and I saw something I\'ve never seen in ObjC before when some Apple engineer talked about a Stack example.

The followi

Answer 1

This is indeed a new language feature, and if you must declare your ivars (rather than simply declaring properties and letting the compiler generate ivars for you) it's a good practice. Your header files in theory should only expose public interface for your classes; everything else belongs in the implementation.

One caveat is that implementation-file ivars are not visible to subclasses, which can occasionally be a little bit awkward if you have manually generated setters and getters that you need to subclass.