A couple of extensions to make working with NSCoding a little nicer using generics

NSCoder+Extensions.swift

extension NSCoder {
    func encode(key: String, value: AnyObject?) {
        self.encodeObject(value, forKey: key)
    }
    func decode<T>(key: String) -> T? {
        return self.decodeObjectForKey(key) as? T
    }
}
extension NSCoding {
    func encode() -> NSData {
        return NSKeyedArchiver.archivedDataWithRootObject(self)
    }
    static func decode(data: NSData) -> Self? {
        return NSKeyedUnarchiver.unarchiveObjectWithData(data) as? Self
    }
}


//USAGE:
class Foo: NSObject, NSCoding {
    var string: String
    var integer: Int?
    
    required init(string: String, integer: Int?) {
        self.string = string
        self.integer = integer
    }
    convenience required init?(coder aDecoder: NSCoder) {
        self.init(
            string: aDecoder.decode("string")!,
            integer: aDecoder.decode("integer")
        )
    }
    func encodeWithCoder(aCoder: NSCoder) {
        aCoder.encode("string", value: self.string)
        aCoder.encode("integer", value: self.integer)
    }
}


let foo = Foo(string: "foo", integer: .None)
let data = foo.encode()
let decodedFoo = Foo.decode(data)
decodedFoo?.string
decodedFoo?.integer