Type safe User defaults.

defaults.swift

import Foundation

@propertyWrapper
struct Defaults<Value> {
    
    let key: Key
    let defaultValue: Value
    
    var wrappedValue: Value {
        get {
            return (UserDefaults.standard.object(forKey: key.rawValue) as? Value) ?? defaultValue
        } set {
            UserDefaults.standard.set(newValue, forKey: key.rawValue)
        }
    }
}

extension Defaults {
    
    enum Key: String {
        
        case isNewUser = "is-new-user"
    }
}

/* Usage */

extension UserDefaults {
    
    @Defaults(key: .isNewUser, defaultValue: true)
    static var isNewUser: Bool
}

print(UserDefaults.isNewUser) // prints true
UserDefaults.isNewUser = false