ios - Variable used before being initialized in function

Question

I'm making a ro sham bo game. Functions in swift are different than what I have used before. I keep getting an error:

Variable used before being initialized in function

What am I doing wrong?

import Foundation
import UIKit
class Result: UIViewController {
    var rval: Int?
    var chosen: Int?
    func determineWinner() -> Int {
        var returnval: Int
        if (chosen == rval){
            returnval = 2
        }
        else if (chosen == 1 && rval == 3){
            returnval = 1
        }
        else if (chosen == 1 && rval == 2){
            returnval = 0
        }
        else if (chosen == 2 && rval == 1){
            returnval = 1
        }
        return (returnval)
    }

    @IBOutlet weak var wl: UILabel!

    @IBAction func PlayAgain(sender: AnyObject) {
    }
    override func viewDidLoad() {
        print(chosen)
    }
}

Answer 1

Every possible path in the flow of a Swift program must have a defined returned value. In your case, if the if/else if/else sections are all skipped, leaving returnval unassigned. Thus, no valid value is being returned. Try this:

import Foundation
import UIKit //space things out to be easier to read

class Result: UIViewController {

    var rval: Int? //these should have better names
    var chosen: Int?

    func determineWinner() -> Int {

        var returnval = -1 //needs a default value

        if (chosen == rval){
            returnval = 2
        }
        else if (chosen == 1 && rval == 3){
            returnval = 1
        }
        else if (chosen == 1 && rval == 2){
            returnval = 0
        }
        else if (chosen == 2 && rval == 1){
            returnval = 1
        }

        return returnval //don't put return value in brackets
    }

    @IBOutlet weak var wl: UILabel!

    @IBAction func PlayAgain(sender: AnyObject) {
    }

    override func viewDidLoad() {
        print(chosen) 
    }
}

This is also a very good candidate for using pattern matching with switch statements. Here's what I think works beside, in conjunction withSean's suggestion.

var determineWinner: Int? {

    guard let chosen = chosen, let rval = rval else {
        //handle error, either chosen or rval is nil
        return nil
    }

    switch ((chosen, rval)) {
    case let (x, y) where x == y: return 2
    case (1, 3): return 1
    case (1, 2): return 0
    case (2, 1): return 1

    default:
        print("handle default case here")
        return nil;
    }
}