lazy-controller.swift

class MainViewController: UIViewController {
    lazy var viewControllers: [UIViewController] = self.lazyControllers.filter { $0 != nil }.map { $0! }
    
    private lazy var lazyControllers: LazyMapSequence<[String], UIViewController?> = {
        let controllerKeys = ["home", "profile", "settings"]
        
        return controllerKeys.lazy.map { key in
            return self.createController(for: key)
        }
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Accessing viewControllers triggers lazy instantiation
        print("ViewControllers count: \(viewControllers.count)")
    }
    
    private func createController(for key: String) -> UIViewController? {
        switch key {
        case "home":
            return HomeViewController()
        case "profile":
            return ProfileViewController()
        case "settings":
            return SettingsViewController()
        default:
            return nil
        }
    }
}