Another statically-typed NSUserDefaults inspired by https://github.com/radex/SwiftyUserDefaults

SmartKey.swift

class SmartKeyBase: Equatable, Hashable {
    private let defaults = NSUserDefaults.standardUserDefaults()
    private(set) static var allKeys = Set<SmartKeyBase>()
    let name: String
    
    static func removeAllValues() {
        allKeys.forEach { $0.removeValue() }
    }
    
    init(_ name: String) {
        self.name = name
        assert(!SmartKeyBase.allKeys.contains(self), "Duplicate SmartKey key found: \(name).")
        SmartKeyBase.allKeys.insert(self)
    }
    
    func hasValue() -> Bool {
        return defaults.objectForKey(name) != nil
    }
    
    func removeValue() {
        defaults.removeObjectForKey(name)
    }
    
    var hashValue: Int {
        return name.hashValue
    }
}

func ==(left: SmartKeyBase, right: SmartKeyBase) -> Bool {
    return left.name == right.name
}

class SmartKey<T>: SmartKeyBase {
    let defaultValue: T
    
    // `value` - default value for this key 
    init(_ name: String, _ value: T) {
        self.defaultValue = value
        super.init(name)
    }
    
    var value: T {
        get {
            if let value = defaults.objectForKey(name) {
                switch value {
                case let data as NSData: return NSKeyedUnarchiver.unarchiveObjectWithData(data) as! T
                default:
                if let value = value as? T {
                        return value
                    }
                    else {
                        removeValue()
                        // warning user?
                        return defaultValue
                    }
                }
            }
            else {
                return defaultValue
            }
        }
        set {
            switch newValue {
            case let value as Int: defaults.setInteger(value, forKey: name)
            case let value as Double: defaults.setDouble(value, forKey: name)
            case let value as Bool: defaults.setBool(value, forKey: name)
            case let value as String: defaults.setObject(value, forKey: name)
            case let value as NSDate: defaults.setObject(value, forKey: name)
            //case let value as NSData: defaults.setObject(value, forKey: name)
            case let value as NSObject where value is NSCoding: defaults.setObject(NSKeyedArchiver.archivedDataWithRootObject(value), forKey: name)
            default: assertionFailure("Unsupported `value` type: \(newValue.dynamicType).")
            }
        }
    }
    
    var optionalValue: T? {
        return hasValue() ? value : nil
    }
}

extension SmartKey: CustomStringConvertible {
    var description: String {
        return "\(name): \(optionalValue), \(defaultValue)"
    }
}

Usage.swift

struct UserDefaults {
    static let currentMap = SmartKey<String>("currentMap", "moscow")
    static let count = SmartKey<Int>("count", 0)
    static let color = SmartKey<UIColor>("color", .whiteColor())
    static let ints = SmartKey<[Int]>("ints", [1, 2])
    static let recentRoutes = SmartKey<[SavedRoute]>("recentRoutes",  []) // @objc(SavedRoute)
// class SavedRoute: NSObject, NSCoding { ... }
    static let date = SmartKey<NSDate>("date", NSDate.distantPast())
    static let dict = SmartKey<[String: SavedRoute]>("dict", ["first": SavedRoute()])
    static let url = SmartKey<NSURL>("url", NSURL(string: "http://localhost")!)
}

UserDefaults.count.value++
UserDefaults.ints.value += [3]
// ...etc.