Swift & NSCoding

NSCodingBox.swift

public final class Box<T> {
    public let value: T
    public init(value: T) {
        self.value = value
    }
}

public final class NSCodingBox<T: Coding>: NSObject, NSCoding {
    public let value: T
    
    public init(value: T) {
        self.value = value
        super.init()
    }
    
    @objc public required init?(coder aDecoder: NSCoder) {
        guard let value = T.decode(with: aDecoder) else { return nil }
        self.value = value
        super.init()
    }
    
    @objc public func encodeWithCoder(aCoder: NSCoder) {
        value.encode(with: aCoder)
    }
}

public protocol Coding {
    func encode(with coder: NSCoder)
    static func decode(with coder: NSCoder) -> Self?
}

extension Coding {
    public func archive() -> NSData {
        return NSKeyedArchiver.archivedDataWithRootObject(NSCodingBox(value: self))
    }
    
    public static func unarchive(data: NSData) -> Self? {
        return (NSKeyedUnarchiver.unarchiveObjectWithData(data) as? NSCodingBox<Self>)?.value
    }
}

struct SomeType: Coding, Equatable {
    let property: String
    
    func encode(with coder: NSCoder) {
        coder.encodeObject(property, forKey: "property")
    }
    
    static func decode(with coder: NSCoder) -> SomeType? {
        guard let property = coder.decodeObjectForKey("property") as? String else { return nil }
        return SomeType(property: property)
    }
}

let value = SomeType(property: "value")
let data = value.archive()
let decoded = SomeType.unarchive(data)

let box = NSCodingBox<SomeType>(value: value)
let data = NSKeyedArchiver.archivedDataWithRootObject(box)
let decoded = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! NSCodingBox<SomeType>