Saving objects to UserDefaults that confirm to a protocol(using protocol oriented programming paradigm) - swift3

Question

I have multiple object types that I want to save to UserDefaults.So, I have written a UserDefaultsManager class where I have methods to save objects in UserDefaults using NSKeyedArchiver and to fetch using NSKeyedUnarchiver.Here are the methods:
class UserDefaultsManager
{
class func saveToUserDefaults(object:Any, Key:String)
{
let data = NSKeyedArchiver.archivedData(withRootObject: object)
UserDefaults.standard.setValue(data, forKey: key)
UserDefaults.standard.synchronize()
}
class func userDefaultsForKey(_ key:String) -> Any
{
let data = UserDefaults.standard.value(forKey: key)
let object = NSKeyedUnarchiver.unarchiveObject(with: data as! Data)
return object as! LoginUser
}
}
As you can see that objects to be saved can be of any type, so I have defined the parameter as 'Any'. Now while I need to fetch the object, I am down casting it to 'LoginUser' object type and then returning it.
I can also add another parameter called 'type' and based on that I can downcast it to that particular type.But that's not the point here.
The point here is that I was thinking of creating a protocol, say,'UserDefaultsPersistence' and only the classes confirming to that protocol can call such methods and be saved in UserDefaults.Here is an example:
class func archiveObject<T:UserDefaultPersistence>(object:T) -> Data
{
let data = NSKeyedArchiver.archivedData(withRootObject: object)
return data
}
But the problem is that when I fetch the object from UserDefaults,I will have to downcast it to that particular object to use its properties.So what's the whole point of using protocols?

Answer 1

The point of using a protocol would be so the programmer knows which objects are and are not explicitly supported for archiving by the app (although, you can still archive other things). Also, since the method signature enforces conformance to the protocol, you will have to make/declare each object conform to it to be able to use it with those methods. This will make your code easier to understand and more type safe, as it will prevent you from accidentally trying to archive or unarchive something which you don't explicitly support.
If you are supporting many objects being archived, I would assume using Core Data would be a better option. In the short term, it will take some time to get set up, but in the long run it will save you time, since you will have access to a strongly typed database. UserDefaults is really for simple things and is not meant to replace a database.