Swift library that makes easier to serialize the user's preferences (app's settings) with system User Defaults or Property List file on disk.
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CI Status Carthage compatible Version Swift License

PersistentStorageSerializable is a protocol for automatic serialization and deserialization of Swift class, struct or NSObject descendant object into and from User Defaults or Property List file.

The adopting type properties must be of property list type (String, Data, Date, Int, UInt, Float, Double, Bool, Array or Dictionary of above). If you want to store any other type of object, you should typically archive it to create an instance of Data. The URL properties can be stored in User Defaults storage but not in Plist storage. In the last case, you have to archive it to/from Data.

The PersistentStorageSerializable protocol provides default implementations of init(from:) initializer and persist() function. The library defines two classes of PesistentStorage protocol: UserDefaultsStorage and PlistStorage. Object of one of those types is passed as the argument when calling to init(from:) initializer to specify which storage to be used for serialization/deserialization.

Functions of the PersistentStorageSerializable protocol traverses the adopting type object and gets/sets it's properties values via Reflection library. The NSObject class descendant properties values are get/set via KVC.

How to use

Serialize/Deserialize a struct with User Defaults by using UserDefaultStorage as shown below:

struct Settings: PersistentStorageSerializable {
    var flag = false
    var title = ""
    var number = 1
    var dictionary: [String : Any] = ["Number" : 1, "Distance" : 25.4, "Label" : "Hello"]

    // MARK: Adopt PersistentStorageSerializable
    var persistentStorage: PersistentStorage!
    var persistentStorageKeyPrefix: String! = "Settings"

// Init from User Defaults
let mySettings = try! Settings(from: UserDefaultsStorage.standard)

mySettings.flag = true

// Persist into User Defaults
try! mySettings.persist()

To serialize data with Plist file use PlistStorage class:

// Init from plist
let plistUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).last!.appendingPathComponent("storage.plist")

let settingsOnDisk = try! Settings(from: PlistStorage(at: plistUrl))

mySettings.flag = true

// Persist on disk
try! mySettings.persist()

Reading data stored by the previous version of the app

When you have some data persisted in User Defaults by the previous version of the app and want to read that data into a structure you need to provide a mapping between properties names and User Defaults keys by overloading the persistentStorageKey(for:) function.

Say we have following data persisted in User Defaults:

UserDefaults.standard.set("Superhero", forKey: "oldGoogTitle")
UserDefaults.standard.set(true, forKey: "well.persisted.option")

We want those to be serialized with the object of ApplicationConfiguration class.

final class ApplicationConfiguration: PersistentStorageSerializable {
    var title = ""
    var showIntro = false

    // MARK: Adopt PersistentStorageSerializable
    var persistentStorage: PersistentStorage!
    var persistentStorageKeyPrefix: String!

// Provide key mapping by overloading `persistentStorageKey(for:)` function.
extension ApplicationConfiguration {
    func persistentStorageKey(for propertyName: String) -> String {
        let keyMap = ["title" : "oldGoogTitle", "showIntro" : "well.persisted.option"]
        return keyMap[propertyName]!

// Now we can load data persisted in the storage.
let configuration = try! ApplicationConfiguration(from: UserDefaultsStorage.standard)

print(configuration.title) // prints Superhero
print(configuration.showIntro) // prints true


To run example projects for iOS/macOS, run pod try PersistentStorageSerializable in the terminal.


  • Xcode 8.3
  • Swift 3.1



PersistentStorageSerializable is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "PersistentStorageSerializable"

and run pods update or pods install.


If you use Carthage to manage your dependencies, simply add PersistentStorageSerializable to your Cartfile:

github "IvanRublev/PersistentStorageSerializable"

If you use Carthage to build your dependencies, make sure you have added PersistentStorageSerializable.framework and Reflection.framework to the "Linked Frameworks and Libraries" section of your target, and have included them in your Carthage framework copying build phase.


Copyright (c) 2017, IvanRublev, ivan@ivanrublev.me


PersistentStorageSerializable is available under the MIT license. See the LICENSE file for more info.