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Re: Retain/Release and Properties clarification
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Re: Retain/Release and Properties clarification


  • Subject: Re: Retain/Release and Properties clarification
  • From: Bayes Scott F <email@hidden>
  • Date: Thu, 13 Oct 2011 10:54:04 -0700

Thank you, David.

Sounds like safety first for my code: always use the setter/getter for synthesized properties, even in self.

Or use ivars.

ScottB

On Oct 12, 2011, at 09:21 , Bayes Scott F wrote:

> Someone on Matt's site mentioned the possibility that the synthesized ivar could be implemented indirectly, say as a member of a collection. Since the implementation's opaque, we don't know if that ever can happen.
>
> So, is self->mySynthIvar safe (both lvalue and rvalue), or should we be messaging?
>
> And does the compiler ever shortcut something like self.mySynthSimpleIntVar to self->mySynthSimpleIntVar, or does it always use the setter/getter?
>
> Thanks
>
>
> ScottB
>
> On Oct 11, 2011, at 10:12 , David Duncan wrote:
>
>> On Oct 11, 2011, at 9:57 AM, Matt Neuburg wrote:
>>
>>> I did everything "right" when I named an ivar "firstResponder" (property, synthesized ivar, synthesized accessors) and totally broke my app because Apple was apparently already using an undocumented ivar called "firstResponder".
>>>
>>> http://www.cocoabuilder.com/archive/cocoa/296662-assign-property-behaves-differently-from-simple-instance-variable.html
>>
>> The problem wasn't an undocumented ivar, it was an undocumented method. The @synthesize thus overrode the existing method and broke your project because parts of UIKit were expecting the default implementation and got your implementation instead.
>>
>> As a rule, we strive to avoid this situation, but unfortunately this does happen on occasion.
>>
>>> Also, note that there are circumstances where a synthesized ivar won't work; see, for instance, this note:
>>>
>>> http://www.cocoabuilder.com/archive/cocoa/298320-inherited-implicitly-created-member-is-no-member.html
>>
>> The gist of this is that synthesized ivars are private, and the public interface (the @property) doesn't tell you about private implementation details (the ivar). As such, subclasses can't get at synthesized ivars, precisely because the @synthesize declaration is hidden from them.
>> --
>> David Duncan
>>
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  • Follow-Ups:
    • Re: Retain/Release and Properties clarification
      • From: David Rowland <email@hidden>
References: 
 >Re: Retain/Release and Properties clarification (From: Matt Neuburg <email@hidden>)
 >Re: Retain/Release and Properties clarification (From: David Duncan <email@hidden>)
 >Re: Retain/Release and Properties clarification (From: Bayes Scott F <email@hidden>)

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