Smart Home Smart Home - 1 year ago 74
Objective-C Question

If a property is defined as copy, do I still need to do a copy when assigning to the ivar?

Suppose I have a property defined as

@property (copy) NSString *name

Suppose I have a
method defined as below.

-(instancetype) initWithName:(NSString *)name
self = [super init];
if (self)
_name = [name copy]; //Do I need this copy or will ARC do it automatically?
return self;

Do I need the copy in the commented line or will ARC handle it based on the
in the property declaration just like it would in the synthesized setter?

Answer Source

The copy applies to the property's synthesized setter method, not the backing instance variable.

Since you are bypassing the property in the initWithName: method and assigning directly to the instance variable, the copy isn't applied automatically.

In order to honor the contract that the value is copied, you should explicitly call copy when you directly assign a value to the instance variable. None of this has to do with ARC (or MRC). It's all about the contract you defined on the property.

tl;dr - yes, you should call copy in the code you posted.

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