Question

I know “id” type, but what does id<Litigating> mean ?

@protocol Litigating
-(int) sue:( id<Litigating> ) someone;
@end

Answer 1

Think of Objective-C protocols as Java, C#, etc. Interfaces on speed.

This is a variable of any class, conforming to the protocol Litigation (this is as far as traditional OOP goes without jumping hoops):

id<Litigation> someone;

This is a variable of the class Company (and subclasses), that also conforms to Litigation:

Company<Litigation>* someone;

This is a variable of class Company, that also conforms to both Litigation and NSCopying**:

Company<Litigation, NSCopying>* someone;