Dependency injection example

WelcomeView+UserDefaults.swift

class WelcomeView {

	private let userDefaults: UserDefaults

	init(userDefaults: UserDefaults) {
		self.userDefaults = userDefaults;
	}

	func viewDidLoad() {
		/// Show onboarding the first time User sees this screen;
		if (userDefaults.bool(forKey: "appHasBeenAlreadyLaunched") == false) {
			print("Welcome to the app! Let me show you the onboarding")
			userDefaults.set(true, forKey: "appHasBeenAlreadyLaunched");
		}
	}
}

struct UserDefaults {
	/// Read some keyed boolean value (on a persistent disk cache, or on a database, on a remote backend, etc.)
	func bool(forKey: String) -> Bool

	/// Write some boolean value (on a persistent disk cache, or on a database, on a remote backend, etc.)
	func set(_ value: Bool, forKey: String) -> Bool
}