Swifty and modern UserDefaults
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Latest commit 9b6b657 Oct 18, 2018


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Swifty and modern UserDefaults

This package is used in production by the Lungo, Battery Indicator, and HEIC Converter app.


  • Strongly typed: You declare the type and default value upfront.
  • Codable support: You can store any Codable value, like an enum.
  • Debuggable: The data is stored as JSON-serialized values.
  • Observation: Observe changes to keys.
  • Lightweight: It's only ~300 lines of code.


  • macOS 10.12+
  • iOS 10+
  • tvOS 10+
  • watchOS 3+



.package(url: "https://github.com/sindresorhus/Defaults", from: "1.0.0")


github "sindresorhus/Defaults"


pod 'Defaults'


You declare the defaults keys upfront with type and default value.

import Cocoa
import Defaults

extension Defaults.Keys {
	static let quality = Key<Double>("quality", default: 0.8)
	//            ^            ^         ^                ^
	//           Key          Type   UserDefaults name   Default value

You can then access it as a subscript on the defaults global (note lowercase):

//=> 0.8

defaults[.quality] = 0.5
//=> 0.5

defaults[.quality] += 0.1
//=> 0.6

defaults[.quality] = "🦄"
//=> [Cannot assign value of type 'String' to type 'Double']

You can also declare optional keys for when you don't want to declare a default value upfront:

extension Defaults.Keys {
	static let name = OptionalKey<Double>("name")

if let name = defaults[.name] {

Enum example

enum DurationKeys: String, Codable {
	case tenMinutes = "10 Minutes"
	case halfHour = "30 Minutes"
	case oneHour = "1 Hour"

extension Defaults.Keys {
	static let defaultDuration = Key<DurationKeys>("defaultDuration", default: .oneHour)

//=> "1 Hour"

It's just UserDefaults with sugar

This works too:

extension Defaults.Keys {
	static let isUnicorn = Key<Bool>("isUnicorn", default: true)

//=> true

Shared UserDefaults

let extensionDefaults = UserDefaults(suiteName: "com.unicorn.app")!

extension Defaults.Keys {
	static let isUnicorn = Key<Bool>("isUnicorn", default: true, suite: extensionDefaults)

//=> true

// Or

//=> true

Use keys directly

You are not required to attach keys to Defaults.Keys.

let isUnicorn = Defaults.Key<Bool>("isUnicorn", default: true)

//=> true

Observe changes to a key

extension Defaults.Keys {
	static let isUnicornMode = Key<Bool>("isUnicornMode", default: false)

let observer = defaults.observe(.isUnicornMode) { change in
	// Initial event
	//=> false
	//=> false

	// First actual event
	//=> false
	//=> true

defaults[.isUnicornMode] = true

Default values are registered with UserDefaults

When you create a Defaults.Key, it automatically registers the default value with normal UserDefaults. This means you can make use of the default value in, for example, bindings in Interface Builder.

extension Defaults.Keys {
	static let isUnicornMode = Key<Bool>("isUnicornMode", default: true)

print(UserDefaults.standard.bool(forKey: isUnicornMode.name))
//=> true


let defaults = Defaults()


Type: class

Stores the keys.

Defaults.Key (alias Defaults.Keys.Key)

Defaults.Key<T>(_ key: String, default: T, suite: UserDefaults = .standard)

Type: class

Create a key with a default value.

The default value is written to the actual UserDefaults and can be used elsewhere. For example, with Interface Builder binding.

Defaults.OptionalKey (alias Defaults.Keys.OptionalKey)

Defaults.OptionalKey<T>(_ key: String, suite: UserDefaults = .standard)

Type: class

Create a key with an optional value.


clear(suite: UserDefaults = .standard)

Type: func

Clear the user defaults.


observe<T: Codable>(
	_ key: Defaults.Key<T>,
	options: NSKeyValueObservingOptions = [.initial, .old, .new],
	handler: @escaping (KeyChange<T>) -> Void
) -> DefaultsObservation
observe<T: Codable>(
	_ key: Defaults.OptionalKey<T>,
	options: NSKeyValueObservingOptions = [.initial, .old, .new],
	handler: @escaping (OptionalKeyChange<T>) -> Void
) -> DefaultsObservation

Type: func

Observe changes to a key or an optional key.

By default, it will also trigger an initial event on creation. This can be useful for setting default values on controls. You can override this behavior with the options argument.


How is this different from SwiftyUserDefaults?

It's inspired by that package and other solutions. The main difference is that this module doesn't hardcode the default values and comes with Codable support.


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MIT © Sindre Sorhus