CODEWITHSUNDEEP
objective-ccocoa-touchautomatic-ref-countingdeclared-property
rustylepord
rustylepord

Reputation: 5801

Should an NSString property under ARC be strong or copy?

When not compiling with ARC, it is recommended to use copy properties for data types such as NSString. I could not find proper documentation on the use of copy in ARC mode. Can someone tell me what's applicable for ARC?

Upvotes: 62

Views: 24248

Answers (4)

Matt Wilding
Matt Wilding

Reputation: 20153

It doesn't matter if you're using ARC or non-ARC.

The reasoning behind the copy is so that you can guarantee that your class' internal state can't be modified from outside the implementation.

This could happen if someone passes you an NSMutableString, and then modifies it later. That consideration is independent of the memory management environment.

Upvotes: 12

Snowcrash
Snowcrash

Reputation: 86057

copy counts as strong. Use:

@property(nonatomic,copy) NSString *name;

https://devforums.apple.com/message/654033#654033

or even:

@property NSString *firstName;

http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/ProgrammingWithObjectiveC/DefiningClasses/DefiningClasses.html#//apple_ref/doc/uid/TP40011210-CH3-SW7

Upvotes: 11

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726479

Copying and ARC are orthogonal: you make copies of mutable objects to "freeze" their state; ARC keeps track of object's reference count.

NSString objects may or may not be mutable. When you receive an NSString* as a parameter, you cannot be certain that it is immutable unless you check its type (and even then you may get false positives). If your algorithm relies on the string not changing after being set, making a copy is the right thing to do. ARC, on the other hand, will ensure that the object is not released while you are holding a strong reference to it.

Upvotes: 14

Joe
Joe

Reputation: 57169

It is still recommended to copy because you want to avoid something passing a mutable string and then changing it without you knowing. A copy guarantees that the string you have will not change.

Upvotes: 82

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