Question

It is casually mentioned here that instance variables have __strong enabled per default – does this mean that having this:

@interface Foo {
    Bar *test; // implicitly __strong
}
@property (nonatomic, unsafe_unretained) Bar *test;
@end

and calling

test = [[Bar alloc] init];

in the implementation file, that the new Bar instance will be retained? If yes, will the Bar instance be released at all when Foo is deallocated, considering that the property tells ARC to not touch it?

Answer 1

Did you try compiling that? It won’t work. The ivar associated with a property has to have the same ownership qualifier as the property. This is in the Clang ARC doc:

If the associated instance variable already exists, then its ownership qualification must equal the ownership of the property; otherwise, the instance variable is created with that ownership qualification.

@interface Digby : NSObject 
{
    NSString * wiska;
}

@property (unsafe_unretained) NSString * wiska;

@end

@implementation Digby

@synthesize wiska;    // Existing ivar 'wiska' for property 'wiska' with unsafe_unretained attribute must be __unsafe_unretained

@end

If you remove the explicit ivar declaration, then the synthesized ivar will be __unsafe_unretained, like the property.