Create the Perfect UserDefaults Wrapper Using Property Wrapper (https://swiftsenpai.com/swift/create-the-perfect-userdefaults-wrapper-using-property-wrapper/)

Property-Wrapper-AppData-Full.swift

struct User: Codable {
    var firstName: String
    var lastName: String
    var lastLogin: Date?
}

@propertyWrapper
struct Storage<T: Codable> {
    private let key: String
    private let defaultValue: T

    init(key: String, defaultValue: T) {
        self.key = key
        self.defaultValue = defaultValue
    }

    var wrappedValue: T {
        get {
            // Read value from UserDefaults
            guard let data = UserDefaults.standard.object(forKey: key) as? Data else {
                // Return defaultValue when no data in UserDefaults
                return defaultValue
            }

            // Convert data to the desire data type
            let value = try? JSONDecoder().decode(T.self, from: data)
            return value ?? defaultValue
        }
        set {
            // Convert newValue to data
            let data = try? JSONEncoder().encode(newValue)
            
            // Set value to UserDefaults
            UserDefaults.standard.set(data, forKey: key)
        }
    }
}

@propertyWrapper
struct EncryptedStringStorage {

    private let key: String

    init(key: String) {
        self.key = key
    }

    var wrappedValue: String {
        get {
            // Get encrypted string from UserDefaults
            return UserDefaults.standard.string(forKey: key) ?? ""
        }
        set {
            // Encrypt newValue before set to UserDefaults
            let encrypted = encrypt(value: newValue)
            UserDefaults.standard.set(encrypted, forKey: key)
        }
    }

    private func encrypt(value: String) -> String {
        // Encryption logic here
        return String(value.reversed())
    }
}

struct AppData {
    @Storage(key: "username_key", defaultValue: "")
    static var username: String

    @Storage(key: "enable_auto_login_key", defaultValue: false)
    static var enableAutoLogin: Bool
    
    // Declare a User object
    @Storage(key: "user_key", defaultValue: User(firstName: "", lastName: "", lastLogin: nil))
    static var user: User
    
    @EncryptedStringStorage(key: "password_key")
    static var password: String
}


AppData.username = "swift-senpai"
print(AppData.username) // swift-senpai

AppData.enableAutoLogin = true
print(AppData.enableAutoLogin)  // true

let johnWick = User(firstName: "John", lastName: "Wick", lastLogin: Date())
AppData.user = johnWick
print(AppData.user.firstName) // John
print(AppData.user.lastName) // Wick
print(AppData.user.lastLogin!) // 2019-10-06 09:40:26 +0000

AppData.password = "password1234"
print(AppData.password) // 4321drowssap

Hi. after restarting i'm losing the data because storage takes default value. what's the best approach to get the data after app restart by using your @propertyWrapper Storage

Data will be lost when you run the code in Xcode Playground. However, if you use it in an app, the data will be persisted.

Hi, very nice implementation.
My question is: How can you inject mock/spy UserDefaults for unit testing?

And addition:

             if let newValue {
                let data = try? JSONEncoder().encode(newValue)
                UserDefaults.standard.set(data, forKey: key)
            } else {
                UserDefaults.standard.removeObject(forKey: key)
            }

If set nil - remove data.