Re: Stupid objective-c question
Re: Stupid objective-c question
- Subject: Re: Stupid objective-c question
- From: Uli Kusterer <email@hidden>
- Date: Sat, 24 Sep 2016 04:15:05 +0200
On 22 Sep 2016, at 02:02, Doug Hill <email@hidden> wrote:
>>> My question is: how can the compiler know that '==' in this case is a NSString comparison?
>>> Or is some other magic going on here? if so, which?
>>> Does the compiler know it should perform some kind of dynamic method dispatch?
>>
>> My guess, without seeing the code that set up the observer, is that it was also set up with @"mediaLibraryLoaded", and the compiler collects and reuses string constants, so the address is the same. I'd guess that if you ensure that the string is a unique variable, it won't work.
>>
>> NSString* s = [NSString stringWithFormat:@"%@%@%@", @"media", @"Library", @"Loaded"];
>> if(context == (__bridge void*)s)
>>
>> Steve via iPad
>
> For the above test, you could also try turning off the LLVM code-gen setting "gcc_reuse_strings".
> (Which parenthetically, you probably wouldn't want to do in shipping code, particularly if you have a lot of strings.)
>
> But yeah, as everyone says, it's generally not a good thing to rely upon this behavior, and just use -[NSString isEqual:]
Do *not* call methods on the context to a KVO observation! It is not guaranteed to actually be an object! It is not storage for user data, it is simply a unique identifier for your subscription to these KVO callbacks.
-- Uli
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