Re: NSManagedObject, NSString property retain vs copy
Re: NSManagedObject, NSString property retain vs copy
- Subject: Re: NSManagedObject, NSString property retain vs copy
- From: Sean McBride <email@hidden>
- Date: Fri, 31 Jul 2015 13:06:58 -0400
- Organization: Rogue Research Inc.
On Fri, 31 Jul 2015 12:15:10 +0200, Jean-Daniel Dupas said:
>
>> Le 30 juil. 2015 à 18:26, Fritz Anderson <email@hidden> a écrit :
>>
>> On 30 Jul 2015, at 11:03 AM, Trygve Inda <email@hidden> wrote:
>>
>>> It seems Apple is using retain rather than copy for NSString properties in
>>> an NSManagedObject subclass.
>>>
>>> I was always under the impression that copy should be used for NSString, so
>>> why the retain??
>>
>> For an immutable string, -copy is implemented as a -retain. -copy is a
>guard against the receiver’s relying on the unchanging contents of a
>string whose contents can be changed. If the contents cannot in fact be
>changed, there’s no point in allocating new memory and copying the bytes
>into it.
>>
>> It’s an implementation detail; what makes you believe it makes a difference?
>
>If it is in the property declaration, it is not an implementation
>detail, it is part of the public API.
>
>And as the receiver can’t guarantee that a passed NSString is not a
>NSMutableString under the hood, it should always declare property as
>copy, so the fact that some sample code (I guess this is what the op is
>talking about) use retain is dubious.
This has long been a weakness in the Core Data ecosystem. Even mogenerator does not have an option to make things 'copy':
<https://github.com/rentzsch/mogenerator/issues/41>
I might take a stab at that next week...
Cheers,
--
____________________________________________________________
Sean McBride, B. Eng email@hidden
Rogue Research www.rogue-research.com
Mac Software Developer Montréal, Québec, Canada
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