DesignPatterns6.swift

class Defaults {
    static var mainFormStates: [Memento] {
        get {
            return UserDefaults.standard.array(forKey: UserDefaultConstants.mainForm.rawValue) as? [Memento] ?? [Memento]()
        }
        set {
            UserDefaults.standard.set(newValue, forKey: UserDefaultConstants.mainForm.rawValue)
            UserDefaults.standard.synchronize()
        }
    }
}

enum UserDefaultConstants: String {
    case mainForm
}