protocol NameType {
    var name: String { get }
}

class UserShort: NameType {

    var id: UInt
    var name: String

    init(id: UInt, name: String) {
        self.id = id
        self.name = name
    }

}

final class UserLong: UserShort {

    var status: String
    var isOnline: Bool

    init(id: UInt, name: String, status: String, isOnline: Bool) {
        self.status = status
        self.isOnline = isOnline
        super.init(id: id, name: name)
    }

}

protocol UserProtocol {
    func sortedByName() -> [UserShort]
}

final class UserCollection: UserProtocol {

    let users: [UserShort]

    init(users: [UserShort]) {
        self.users = users
    }

    func sortedByName() -> [UserShort] {
        return users.sorted { $0.name > $1.name }
    }

}

let follower = UserShort(id: 1, name: "Medium Guest")
let currentUser = UserLong(id: 999, name: "Maxim Vialykh", status: "Work on SOLID Arcticle", isOnline: true)
let userCollection = UserCollection(users: [currentUser, follower])
let sorted = userCollection.sortedByName()

for case let user as UserLong in sorted {
    print("UserLong: \(user.name)")
}