Re: Problem Archiving/Un-archiving Custom Objects
Re: Problem Archiving/Un-archiving Custom Objects
- Subject: Re: Problem Archiving/Un-archiving Custom Objects
- From: "Clark S. Cox III" <email@hidden>
- Date: Fri, 22 Jan 2016 08:15:22 -0800
> On Jan 22, 2016, at 06:14, Dave <email@hidden> wrote:
>
>
>> On 21 Jan 2016, at 23:40, Quincey Morris <email@hidden> wrote:
>>
>> On Jan 21, 2016, at 15:22 , Dave <email@hidden <mailto:email@hidden>> wrote:
>>>
>>> I’m relying of the copy attribute for the NSString’s, do I need to change these to do a [xxxxxxx copy] too
>>
>> If you’re writing the setter yourself, you must do the copy yourself. If you’re using the synthesized setter, it’s done for you.
>>
>> In your own code, you may as well be liberal with ‘copy’. It’s basically free (in run-time cost) in situations where you don’t need it. You don’t save anything by leaving it out.
>>
>
> I’ve always been confused over what *actually* happens when you do something like this:
>
> @property (copy) NSString* pString;
>
>
> self.pString = [anotherString copy];
>
> Do two new NSString objects get created? (I mean using the synthesized setter)
The -copy method is called twice, but what that means in practical terms depends on the object being copied.
If you're talking about NSString specifically, zero copies get created, as -copy on immutable foundation types is equivalent to -retain (or is a no-op under ARC).
If "anotherString" is an NSMutableString, then one copy will be created by the explicit call to -copy in your example. But that copy will, itself, be an immutable NSString, so the second copy will be a no-op.
And, of course, if we were talking about some other class that doesn't have a similar optimization, two copies will be created.
Regardless of the circumstances, that explicit copy is redundant (but harmless) under ARC, and will cause a memory leak under MRR.
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