• Upgrade to and require Swift 5. https://github.com/sindresorhus/Defaults/commit/908d3b4ee17e4f7534750d55a0fa2e532ff4f18b

Key observation

You can now observe changes to keys in a strongly-typed fashion. It even preserves the type of the oldValue and newValue keys in the change event.

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

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

	// First actual event
	print(change.oldValue)
	//=> false
	print(change.newValue)
	//=> true
}

defaults[.isUnicornMode] = true

Shorter syntax

 extension Defaults.Keys {
-	static let quality = Defaults.Key<Double>("quality", default: 0.8)
+	static let quality = Key<Double>("quality", default: 0.8)
 }

Support for alternative UserDefaults suites

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

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

defaults[.isUnicorn]
//=> true

// Or

extensionDefaults[.isUnicorn]
//=> true

Registers default values with the native UserDefaults

When you use, for example:

extension Defaults.Keys {
	static let quality = Key<Double>("quality", default: 0.8)
}

It will register 0.8 as the default value with UserDefaults, which can then be used in other contexts, like binding in Interface Builder.