Strongly Typed NSCoding

SwiftNSCoding.swift

public protocol NSCodingKey: RawRepresentable { }

extension NSCoder{
    
    func encodeObject<T where T:NSCodingKey, T.RawValue == String>(objv: AnyObject?, forKey key: T) {
        self.encodeObject(objv, forKey: key.rawValue)
    }
    
    func decodeObjectForKey<T where T:NSCodingKey, T.RawValue == String>(key: T) -> AnyObject?{
        return decodeObjectForKey(key.rawValue)
    }
    
}


class Book : NSObject, NSCoding {
    
    let title:String
    let author:String
    
    private enum BookKey: String, NSCodingKey {
        case Title
        case Author
        
    }
    
    required init(coder aDecoder: NSCoder) {
        self.title  = aDecoder.decodeObjectForKey(BookKey.Title) as! String
        self.author = aDecoder.decodeObjectForKey(BookKey.Author) as! String
    }
    
    
    func encodeWithCoder(aCoder: NSCoder) {
        aCoder.encodeObject(self.title, forKey: BookKey.Title)
        aCoder.encodeObject(self.author, forKey: BookKey.Author)
    }
}