Swift Value of type “ViewController” has no member named “Self” error

Question

I am trying to understand trailing edge closures in Swift, and this code gives me an error in the promptForAnswer() . Specifically, I am getting an Xcode error which says:

Value of type "ViewController" has no member named "Self"

...even though I have declared it in the code.

Can someone explain what is wrong?

import UIKit
import GameplayKit

var allWords = [String]()
var usedWords = [String]()

class ViewController: UITableViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(promptForAnswer))

        if let startWordsPath = Bundle.main.path(forResource: "start", ofType: "txt") {
            if let startWords = try? String(contentsOfFile: startWordsPath) {
                allWords = startWords.components(separatedBy: "\n")
            }
        } else {
            allWords = ["silkworm"]
        }
        startGame()
    }

    @objc func promptForAnswer() {
        let ac = UIAlertController(title: "Enter answer", message: nil, preferredStyle: .alert)
        ac.addTextField()

        let submitAction = UIAlertAction(title: "Submit", style: .default) {
            [unowned self, ac] (action: UIAlertAction) in
            let answer = ac.textFields![0]
            self.submit(answer: answer.text!) // Value of type "ViewController" has no member type "self"
        }

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

    func startGame() {
        allWords = GKRandomSource.sharedRandom().arrayByShufflingObjects(in: allWords) as! [String]
        title = allWords[0]
        usedWords.removeAll(keepingCapacity: true)
        tableView.reloadData()
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return usedWords.count
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Word", for: indexPath)
        cell.textLabel?.text = usedWords[indexPath.row]
        return cell
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

Answer 1

When I pasted your code into a playground in Xcode 9.2 using the default toolchain (Swift 4.0), I got this error on the line you indicated:

Value of type 'ViewController' has no member 'submit'

You can resolve this error by adding a method to your controller that looks like this:

func submit(answer: String) {
  // ...
}

Maybe there was a bug in whatever compiler version you were using. Or maybe it was just having a bad day. Sometimes weird things happen. ¯\\_(ツ)_/¯

Things can change a lot between even minor versions of Swift, so make sure to include the versions of Xcode and the toolchain you are using. It makes reproducing your experience significantly easier.