Do properties default to nil?

Question

If i don't use an ivar for properties, but do this:

@interface someClass : NSObject

@property (nonatomic, retain) NSArray * someArray;

@end

@implementation someClass

@synthesize someArray = _someArray;

- (void) someMethod
{
    if( self.someArray == nil ){
        // True on the first call?
    }
}


@end

The first time I check self.someArray it returns nil, as does _someArray, but is this guaranteed? I read only that ivars are guaranteed to be nil, and since I don't declare a ivar (_someArray is not an ivar), I am not sure if it will be nil everywhere and every time.

score 4 · Accepted Answer · answered Dec 29 '11 at 16:46

4

It's always nil. Objective-C initialises all the variables in a class to nil when it is allocated. Synthesised ivars follow the same rules.

answered Dec 29 '11 at 16:46

joerick

16,078
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score 3 · Answer 2 · answered Dec 29 '11 at 16:45

3

Properties are backed by instance variables if they are synthesized automatically -- so yes, by default such properties will return nil.

answered Dec 29 '11 at 16:45

mipadi

398,885
90
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479

score 2 · Answer 3 · answered Dec 29 '11 at 16:45

2

Yes, all properties, ivars and static variables have always been defined to be initialized to nil. Now with ARC this carries over to __strong stack variables (__strong being the default for all object pointers).

answered Dec 29 '11 at 16:45

Joshua Weinberg

28,598
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Do properties default to nil?

3 Answers3