Simple NSCoding with Swift example, using enum & rawValue for the key names.

Person.swift

@objc(Person)
final public class Person : NSCoding {
    
    public var firstName:String
    public var lastName:String

    private enum SerializationKeys : String {
        case FirstName
        case LastName
    }
    
    init(firstName:String,lastName:String) {
        self.firstName = firstName
        self.lastName = lastName
    }
    
    // MARK: NSCoding
    public required init(coder aDecoder: NSCoder) {
        title = aDecoder.decodeObjectForKey(SerializationKeys.FirstName.rawValue) as! String
        number = aDecoder.decodeObjectForKey(SerializationKeys.LastName.rawValue) as! String
    }
    
    public func encodeWithCoder(encoder: NSCoder) {
        encoder.encodeObject(firstName, forKey: SerializationKeys.FirstName.rawValue)
        encoder.encodeInteger(lastName, forKey: SerializationKeys.LastName.rawValue)
    }
}