We had no choice but to do that, because the handler parameter for UIAlertAction expects a method that takes itself as a parameter, and we also added a default value of “nil” so we could call it ourselves – hence the ! part. And that's what's happening here: we're giving the UIAlertAction some code to execute when it is tapped, (I kno that this code will be executed after the user tapped the button on the alert)

"and it wants to know that that code accepts a parameter of type UIAlertAction." <-> don't really get the idea from this last line,

And this is the closure:

@objc func promptForAnswer() { let ac = UIAlertController(title: "Enter answer", message: nil, preferredStyle: .alert) ac.addTextField() // Creates and alert and adds a textfield to the alert for the user to submit an answer

    // Creates the submit button of the alert on what the user will be able to tap after provided an answer
    let submitAction = UIAlertAction(title: "Submit", style: .default) { [weak self, weak ac] _ in
        guard let answer = ac?.textFields?[0].text else { return }
        self?.submit(answer)
    }

    ac.addAction(submitAction)
    present(ac, animated: true)
}

func submit(_ answer: String) {

}