If a category I'm creating for a class adds methods that also fulfill the contract set out by a protocol, I'd like to flag that category class as implementing the protocol, and thereby indicate to the Obj-C pre-processor that the class effectively implements the protocol as well.
Example delegate (for clarity, thanks Ole!):
@protocol SomeDelegate <NSObject>
- (void)someDelegateMessage;
@end
Example category:
@interface NSObject (SomeCategory) <SomeDelegate>
- (void)someDelegateMessage;
@end
And with an otherwise typical implementation
@implement NSObject (SomeCategory)
- (void)someDelegateMessage {}
@end
When I actually try this, I get a warning for each NSObject method:
warning: incomplete implementation of category 'SomeCategory'
warning: method definition for '-description' not found
...
warning: method definition for '-isEqual:' not found
warning: category 'SomeCategory' does not fully implement the 'NSObject' protocol
Works fine if I remove <SomeDelegate> from the declaration, but of course NSObject isn't recognized as a SomeDelegate