What are the new type qualifiers introduced with ARC?

Question

Automatic Reference Counting (ARC) introduces some new type qualifiers. I\'ve seen __strong and __weak, but what do they do?

Answer 1

Strong tells ARC to retain the property.

@property (strong,nonatomic) NSObject *object;
@property (retain,nonatomic) NSObject *object;

Weak is essentially assign, a unretained property. Except the when the object is deallocated the weak pointer is automatically set to nil.

@property (weak,nonatomic) NSObject *object;
@property (assign,nonatomic) NSObject *object;

Weak is only available on iOS 4.3 and up. If you want to target iOS 4.2 you need to use unsafe_unretained, that will work exactly like assign used to.