What does < > mean / represent in a class interface?

Question

I am sure I have read this somewhere, Can anyone tell me what the < > represent in the following interface?

@interface GameFinder : NSObject 

        

Answer 1

The angle brackets in an interface declaration denote the list of Objective-C protocols that the interface implements. In this case, that GameFinder conforms to the NSNetServiceBrowserDelegate protocol. The Objective-C Language Reference has a full section on protocols (and is a reference you should keep handy in general while learning Objective-C). Basically, a Protocol is an interface that describes the methods a class must implement to conform to that protocol. Classe interfaces may declare, using the angle bracket notation, that they conform to (implement) a protocol. The compiler will check protocol conformance if you provide protocol information in type declarations:

@interface Foo 
...

- (void)methodRequiringBar:(id)arg;
@end

@interface Foo2 
...
@end


id v = [[Foo alloc] init]; //OK
id v = [[Foo alloc] init]; //warning

[v methodRequiringBar:[[Foo2 alloc] init]]; //warning

The compiler will also warn you if a class interface declares conformance to a protocol but not all of the required methods in that protocol are implemented by the class' implementation:

@protocol Bar
@required
- (void)requiredMethod;
@optional
- (void)optionalMethod;
@end

@interface Foo 
...
@end

@implementation Foo
- (void)optionalMethod {
...
}
@end

will give a warning that the Bar protocol is not fully implemented.