Collection callbacks and toll free bridging

[Christiaan Hofman]

On 2 Apr 2008, at 4:45 PM, Adam R. Maxwell wrote:

>
> On Apr 2, 2008, at 7:25 AM, Christiaan Hofman wrote:
>> Hi all,
>>
>> I have some questions about how toll free bridging handles  
>> callbacks for collections. I've searched the docs but came out  
>> empty. Basically I have the following 2 questions:
>>
>> 1. Are Cocoa accessors doing anything besides some checking and  
>> wrapping CF functions?
>> 2. What callbacks are used by collections initialized using Cocoa?
>>
>> Let me make this a bit more explicit for the example of  
>> CFMutableDictionaryRef/NSMutableDictionary. NSMutableDictionary is  
>> documented to copy the keys. So a more concrete version of my  
>> question is: are the keys copied by the Cocoa methods, or by the CF  
>> key callbacks?
>>
>> Context: I need a dictionary for keys that do not conform to  
>> NSCopying. So can I use just use CFDictionaryCreateMutable to  
>> create the dictionary and then use Cocoa methods for the rest?
>
> No, NSMutableDictionary is weird about this.  You must not use - 
> setObject:forKey: because the copying is done in that method.  Mike  
> Ash pointed this out to me on cocoa-dev a couple of years ago:
>
> http://www.cocoabuilder.com/archive/message/cocoa/2006/5/13/163439
>
> My bug report on this was duped to his, and the conclusion is that  
> if you use setObject:forKey:, it will create a copy of your key,  
> then invoke your custom callbacks /on the copy/:
>
> http://www.cocoabuilder.com/archive/message/cocoa/2006/7/10/167259
>
> Once you've used CFDictionaryAddValue, you can safely use  
> objectForKey: and other Cocoa methods, though.  I still think the  
> setObject:forKey: behavior is wrong, but at least I can avoid it.
>
> -- 
> adam

Thanks Adam. Now my question was general, and this is just a specific  
example. Does anyone know the general story for any collection? Or is  
the general story that I cannot trust toll free bridging for anything?

Christiaan