Does Cocoa have a @protocol for iterable / collection objects?

Question

I'm writing an API, and I'm a firm believer of putting as much type safety as possible into APIs. Is there a @protocol for things like NSSet, NSArray, etc that marks it as "iterable" in a for (foo in bar) {..} style loop? At the moment I've got something like this:

- (void) doSomethingWith:(id)someItems;

When I'd like to have something along these lines:

- (void) doSomethingWith:(id <NSIterableCollection>)someItems;

Is it doable? Does wanting it make me some kind of static-typing weanie who has no place doing Obj-C? ;-)

Answer 1

Yes. NSFastEnumeration.

Answer 2

It is doable, though very uncommon. Many Cocoa APIs are not designed with this level of generality in mind. But if you prefer to design your APIs this way, you have options.

One option is to design your API to take an NSEnumerator, and then any class which can provide an NSEnumerator can be used with it.

Another choice is to use anything that conforms to NSFastEnumeration, which allows you to use the for (... in ...) syntax to enumerate the collection.

Answer 3

Objects that want to support enumeration using the standard Objective-C fast enumeration (for..in construct), must impelement the NSFastEnumeration. NSArray, NSDictionary, NSSet and NSEnumerator adopt this protocol.