Question

I found such code on this site:

 - (NSArray *) valueForKey:(id)key {
  NSMutableArray *retval = [NSMutableArray array];

  for (NSObject *object in self) {
    [retval addObject:[object valueForKey:key]];
  }

  return self;
}

Sorry for the newbie question, but I can’t figure out what is fast enumerated there, as self is just an object, not a collection.

Answer 1

Any class that conforms to the NSFastEnumeration protocol can be enumerated with the in syntax. The code snippet you posted implies that the class also implements the -countByEnumeratingWithState:objects:count: method defined by the protocol, and that that method returns an array of NSObject instances to iterate over.