> On Sep 21, 2016, at 18:44, Gabriel Zachmann <z...@tu-clausthal.de> wrote:
> I've got a stupid, curious question regarding a code snippet that I have 
> found on the net (I tried it, it works).
> Here is the code snippet:
> - (void) observeValueForKeyPath: (NSString *) keyPath   ofObject: (id) object
>                        change: (NSDictionary *) change context: (void *) 
> context
> {
>   if ( context == (__bridge void *) @"mediaLibraryLoaded" )
>   {
>     // ...
> 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", 
if(context == (__bridge void*)s)

Steve via iPad


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