Re: Releasing properties?
Re: Releasing properties?
- Subject: Re: Releasing properties?
- From: じょいすじょん <email@hidden>
- Date: Sat, 27 Aug 2016 23:41:08 +0900
> On 2016 Aug 27, at 23:31, Keary Suska <email@hidden> wrote:
>
>
>> On Aug 27, 2016, at 8:22 AM, じょいすじょん <email@hidden> wrote:
>>
>>
>>> On 2016 Aug 27, at 23:09, Keary Suska <email@hidden> wrote:
>>>
>>>>
>>>> On Aug 27, 2016, at 5:22 AM, Andreas Falkenhahn <email@hidden> wrote:
>>>>
>>>> Consider the following example properties:
>>>>
>>>> NSApplication: @property(strong) NSMenu *mainMenu
>>>> NSFont: @property(readonly, copy) NSString *familyName
>>>> NSColorPanel: @property(copy) NSColor *color
>>>>
>>>> AFAIU I must not release the NSMenu/NSString/NSColor obtained from these
>>>> properties because I don't own the objects returned by those properties and
>>>> Apple's memory management policy docs clearly say:
>>>>
>>>> "You must not relinquish ownership of an object you do not own"
>>>>
>>>> So I think I've got that right but I'd be glad if somebody could just
>>>> confirm that I got it right ;)
>>>>
>>>> I'm just a little confused because of the keywords "strong" and "copy" in
>>>> the @property declarations but AFAIU these only refer to setting those
>>>> properties, not getting those properties, i.e. the object is copied when
>>>> *setting* the property, not when *getting* it. Right?
>>>>
>>>> And another question: Can it also happen that a class has a property
>>>> which returns an object which I *must* release or is it a general rule
>>>> that getting a @property always returns objects which I do not own
>>>> and hence mustn't released?
>>>
>>> There are only specific method conventions that establish ownership: alloc+init and new. This is because ownership should only be granted when specifically requested by the caller. There is no good reason for an object to require that a caller own a returned object. Now, some API could decide to buck the convention and have a different object construction naming, but the point is the same. If an API does anything else, it is badly designed. Cocoa will never do this.
>>>
>>> One could even argue (and some have) that there is no good reason for *any* object method to return a retained object, as that forces the caller to explicitly require ownership. And that is key: ownership is a function of the caller, not the object.
>>>
>>> HTH,
>>>
>>> Keary Suska
>>> Esoteritech, Inc.
>>> "Demystifying technology for your home or business"
>>>
>>>
>> Just to keep everyone on the rules, I'm going to post the docs links.
>> It's too easy to quote it wrong. (not saying anybody did)
>>
>> Objective-C
>>
>> https://developer.apple.com/library/mac/documentation/General/Conceptual/DevPedia-CocoaCore/MemoryManagement.html
>>
>> https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/MemoryMgmt/Articles/MemoryMgmt.html
>>
>> Core Foundation (because you WILL use it at some point)
>>
>> https://developer.apple.com/library/mac/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html
>
> Doh! Forgot “copy”. Best to point to docs since they are clear and succinct.
>
Easy to mess up :)
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