iOS Protocol of delegate or source class, which is defined first ?

Hi everyone,

I've used delegate many times, but i've just realized something that i dont know why it can be like that.
Let say a class A has a delegate which implements a protocol B.

- Class A :
@interface A : NSObject {
id<B> delegate;
}
@end

- Protocol B :
@protocol B
- object : (A *) a doSomething : (SomeClass *) s
@end

Because A references B, B references A, I dont know how can i define both things. I know it's possible (the UITableView and UITableViewDelegate is an example), but i dont know how. I've tried to go arround this problem but the compiler keeps giving me errors.

Thanks for reading my post.

I know about @class, but i dont know that we can use @protocol the same way.

Thanks a lot.