enum State: Int {
    case idle
    case waiting
    case failed
    case succeeded
}

extension State: ISyncItem {
    // should be unique across all item types
    static var syncTypeId: ISyncItemType {
        return "state"
    }
    
    // you should return property-list data types (numbers, string, data etc)
    var syncValue: Any {
        return self.rawValue
    }
    
    static func instatiate(with syncValue: Any) -> ISyncItem? {
        if let rawValue = syncValue as? Int {
            return State(rawValue: rawValue)
        }
        return State.idle
    }
}

// listen incoming messages (on both iOS and watchOS)
GenericSyncService.setSyncTipes(types: [State.self]) // On both iOS and watchOS apps

GenericSyncService.default.onReceived(type: State.self) { (state) in
    print("state received: ", state.rawValue)
}

// send message (on both iOS and watchOS)
GenericSyncService.default.send(State.waiting)

public class User: Codable {
    var id       = UUID()
    var name     = ""
    var children = [User]()
    init(name: String) {
        self.name = name
    }
}

extension Array: ISyncItem where Element == User {
    public static var syncTypeId: ISyncItemType {
        return "users"
    }
    
    public var syncValue: Any {
        return try! JSONEncoder().encode(self)
    }
    
    public static func instatiate(with syncValue: Any) -> ISyncItem? {
        if let data = syncValue as? Data {
            return try? JSONDecoder().decode([User].self, from: data)
        }
        return nil
    }
}

let child = User(name: "Ivan")
let father = User(name: "Alex")
father.children = [child]

GenericSyncService.setSyncTipes(types: [User.self])

GenericSyncService.default.onReceived(type: [User].self) { (users) in
    print("received users")
}

GenericSyncService.default.send([father])