6

In the vein of...

@implementation MyClass
- (id) objectForKeyedSubscript:(id)k { 
       return [self something:k]; 
}

Is it also possible to "subscript" Class objects? I too, am about to find out, with you.. but thought I would post this question as I tested it out, myself... 

+ (id) objectForKeyedSubscript:(id)k { 
       return [self.shared something:k]; 
}

And alas.. it is not...

id x = MyClass[@"document"];

error: unexpected interface name 'MyClass': expected expression

But why, Daddy? Class' sure get the short end of NSObject's stick, if you ask me.

Alex Gray
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  • I'd suggest create global pointer at shared instance if you don't want write long code `MyClass.shared[@"document"];` – Cy-4AH May 03 '14 at 06:01
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    You're using the _type name_. Try it with a class object in a variable. `id myClass = [MyClass class]; myClass[@"document"];` Or `[MyClass class][@"document"]`. – jscs May 03 '14 at 16:17
  • Okay, I just grasped why you think that should work -- the subscript is turned into a message send, and the class name is valid as the reciever of a message send. It wouldn't surprise me, though, that the parser will only accept a _literal_ message send (or the dot syntax). – jscs May 03 '14 at 16:25
  • @Cy-4AH My current approach is to usually just create C functions that do roughly the same as you suggest.. `id MyClassReaper(NSString *str) { return objc_msgSend(MyClass.class, NSSelectorFromString(str)); }`, etc... Again, these examples are only illustrative. – Alex Gray May 03 '14 at 19:13

1 Answers1

5

Josh Caswell's comment pointed out the problem:

You're using the type name. Try it with a class object in a variable. id myClass = [MyClass class]; myClass[@"document"]; Or [MyClass class][@"document"]

I SWEAR I had tried that. BIBLE. But the proof is in the pudding...

@interface MyClass : NSObject
@property (readonly) id  boring;
@end
@implementation MyClass
- boring   { return @"typical"; }
+ document { return  @"YEEHAW"; }
- objectForKeyedSubscript:key { return [self valueForKey:key]; }
+ objectForKeyedSubscript:key { 
  return [self performSelector:NSSelectorFromString(key)]; 
}
@end

...

id a = MyClass.new;
id x = a[@"boring"];   // "typical" (via "normal" keyed subscription)
id b = MyClass.class;
   x = z[@"document"]; // "YEEHAW" (via CLASS keyed-subscript!)

or for all my one-liner freaky-deaky's out there...

x = ((id)MyClass.class)[@"document"] // "YEEHAW"
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Alex Gray
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