なんかUserDefaultsをちょっと楽に使う何か

LocalPreference.swift

protocol LPType {
    associatedtype ValueType
    static var value: ValueType? {get set}
    static func val() -> ValueType?
}

extension LPType {
    static var value: ValueType? {
        get { return Self.val() }
        set { Self.set(newValue) }
    }

    private static var name: String { return "\(Self.self)"}

    private static func set(object: ValueType?) {
        if let object = object as? AnyObject? {
            NSUserDefaults.standardUserDefaults().setObject(object, forKey: name)
        }
    }
}

extension LPType where ValueType == String {
    static func val() -> ValueType? {
        return NSUserDefaults.standardUserDefaults().stringForKey(name)
    }
}

extension LPType where ValueType == Int {
    static func val() -> ValueType? {
        return NSUserDefaults.standardUserDefaults().integerForKey(name)
    }
}

extension LPType where ValueType == Bool {
    static func val() -> ValueType? {
        return NSUserDefaults.standardUserDefaults().boolForKey(name)
    }
}

extension LPType where ValueType == Double {
    static func val() -> ValueType? {
        return NSUserDefaults.standardUserDefaults().doubleForKey(name)
    }
}

struct LocalPreference {
}

extension LocalPreference {
    class Hoge: LPType { typealias ValueType = String }
    class Fuga: LPType { typealias ValueType = Bool }
}

print(LocalPreference.Hoge.value)
LocalPreference.Hoge.value = "A"