Declaring a class that works with a constrained generic type

The following lines declare a PartyError enum that conforms to the ErrorType protocol. This way, we will be able to throw a specific exception in the next class that we will create:

public enum PartyError: ErrorType {
    case InsufficientMembersToRemoveLeader
    case InsufficientMembersToVoteLeader
}

The following lines declare a Party class that takes advantage of generics to work with many types. The class name is followed by a less than sign (<), a T that identifies the generic type parameter, a colon (:), and a protocol name that the T generic type parameter must conform to, which is the AnimalProtocol protocol. Then, the where keyword, followed by T (which identified the type) and a colon (:) that indicates that the T generic type parameter has to be a type that also conforms to another protocol—that is, the Equatable protocol. Finally, the greater than sign (>) ends the type constraints declaration that is included...