Archiving of value types in Swift

SwiftValuesArchiving.playground

import Foundation

struct Car {
    var number: Int
}

protocol Archivable {
    func archive() -> NSData
    static func unarchive(data: NSData) -> Self?
}

extension Car: Archivable {

    func archive() -> NSData {
        let data = NSMutableData()
        let archiver = NSKeyedArchiver(forWritingWithMutableData: data)
        archiver.outputFormat = NSPropertyListFormat.XMLFormat_v1_0

        archiver.encodeInteger(number, forKey:"number")

        archiver.finishEncoding()
        return data
    }

    static func unarchive(data: NSData) -> Car? {
        let unarchiver = NSKeyedUnarchiver(forReadingWithData: data)
        let number = unarchiver.decodeIntegerForKey("number")

        return Car(number: number)
    }
}

let a = Car(number: 5)
let data = a.archive()
let b = Car.unarchive(data)
b?.number