class Contact : JSONSerializable {
    var first: String?  
    var last: String?   
    var addr: Address?

    required init() {}

    class func map(source: JsonSZ, object: Contact) {
        object.first <= source["first"]
        object.last <= source["last"]
        object.addr <= source["addr"]
    }
}

class Address: JSONSerializable {

    var street: String?
    var poBox: Int?
    var city: String?
    var country: String?

    var arr:[String]

    required init() {}

    class func map(source: JsonSZ, object: Address) {
        object.street <= source["street"]
        object.poBox <= source["poBox"]
        object.city <= source["city"]
        object.country <= source["country"]
    }
}

// construct object
let address =  Address()
address.street = "Street"
address.poBox = 100
address.city="New York"
address.country = "US"

let user = User()
user.first = "John"
user.last = "Doe"
// assign Address to User
user.addr = address

// initialize serializer
let serializer = JsonSZ()

// serialize ToJSON
let JSON = serializer.toJSON(user)
// ..send json to server

// serialize fromJSON
let user = serializer.fromJSON(JSON, to:User.self)

// user now should be initialized
println(user.first!)
...