実装

extension UIAlertController {
    static func noButtonAlert(title: String?, message: String?) -> UIAlertController {
        return UIAlertController(title: title, message: message, preferredStyle: .alert)
    }
    static func okAlert(title: String?,
                        message: String?,
                        okHandler: ((UIAlertAction) -> Void)? = nil) -> UIAlertController {
        let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
        alert.addAction(.init(title: "OK", style: .default, handler: okHandler))
        return alert
    }

    static func errorAlert(title: String? = "⚠️",
                           error: Error,
                           okHandler: ((UIAlertAction) -> Void)? = nil) -> UIAlertController {
        let alert = UIAlertController(title: title, message: "\(error)", preferredStyle: .alert)
        alert.addAction(.init(title: "OK", style: .default, handler: okHandler))
        return alert
    }

    static func fieldAlert(title: String?,
                           message: String?,
                           placeholder: String?,
                           handler: ((String?) -> Void)? = nil) -> UIAlertController {
        let alert = UIAlertController(title: title, message: message, preferredStyle: .alert)
        alert.addTextField {
            $0.placeholder = placeholder
        }
        alert.addAction(.init(title: "OK", style: .default, handler: { (action: UIAlertAction) in
            handler?(alert.textFields?.first?.text)
        }))
        alert.addAction(.init(title: "Cancel", style: .cancel, handler: { (action) in
            handler?(nil)
        }))
        return alert
    }
}

extension UIViewController {
    func present(_ alert: UIAlertController, completion: (() -> Void)? = nil) {
        present(alert, animated: true, completion: completion)
    }

    func present(_ alert: UIAlertController, _ autoDismissInterval: TimeInterval, completion: (() -> Void)? = nil) {
        present(alert, animated: true, completion: { [weak self] in
            DispatchQueue.main.asyncAfter(deadline: .now() + autoDismissInterval) {
                self?.dismiss(animated: true, completion: completion)
            }
        })
    }
}

使い方

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        // OKボタンのみのAlertを表示
        present(.okAlert(title: nil, message: "グループを作成しました"))

        // OKボタンのついたErrorを表示するAlertを表示
        present(.errorAlert(error:　NSError(domain: "hoge", code: 0, userInfo: nil)) { _ in
        // ユーザが閉じたあとに行う処理を記述
        })

        // UITextFieldつきのAlertを表示
        present(.fieldAlert(
            title: "グループの作成", message: "グループ名を入力してください", placeholder: "グループ名",
            handler: { [weak self] (inputText) in
                // 入力されたテキストを使う処理を記述
        }))

        // 0.3秒後に自動で閉じる
        present(.noButtonAlert(title: "✅", message: "保存しました"), 0.3) { [weak self] in
            // ユーザが閉じたあとに行う処理を記述
        }
    }
}