Question

I have this in my interface:

@property (nonatomic, weak) NSTimeInterval *timeStamp;

Which my logic told me, I need a time stamp object, that only is going to be used by this class within the context of its instantiation, so “weak” seemed to be logical to me– but XCode tells me “property with ‘weak’ attribute must be of object type”… If I just do:

@property (nonatomic) NSTimeInterval *timeStamp;

Then the error goes away, but I am not sure I understand why…

Answer 1

The problem is that NSTimeInterval is a value type — it’s an alias for double, essentially (check NSDate.h for the typedef). The weak attribute only applies to objects that have a retain count (that is, anything that descends from NSObject or NSProxy).

As such, storing a pointer to NSTimeInterval is probably a mistake on your part. You will most likely never receive a pointer to an NSTimeInterval unless you’re expected to write to a given address as an output to a function (probably a callback in such a case). That said, I’m not aware of any functions with NSTimeInterval * as a return type nor any that pass the same to a callback.