如何在分配值时使用Swift循环整个字母表？

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var strWordValue: UILabel!
    @IBOutlet weak var strInputField: UITextField!


    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view,typically from a nib.
    }

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

    @IBAction func sumLettersAction(sender: AnyObject) {
        strWordValue.text = strInputField.text?.wordValue.description

    }

}

扩展

extension String {
    var letterValue: Int {
        return Array("abcdefghijklmnopqrstuvwxyz".characters).indexOf(Character(lowercaseString))?.successor() ?? 0
    }
    var wordValue: Int {
        var result = 0
        characters.forEach { result += String($0).letterValue }
        return result
    }
}

func letterValue(letter: String) -> Int {
    return Array("abcdefghijklmnopqrstuvwxyz".characters).indexOf(Character(letter.lowercaseString))?.successor() ?? 0
}

func wordValue(word: String) -> Int {
    var result = 0
    word.characters.forEach { result += letterValue(String($0)) }
    return result
}


let aValue = letterValue("a")  // 1
let bValue = letterValue("b")  // 2
let cValue = letterValue("c")  // 3
let zValue = letterValue("Z")  // 26

let busterWordValue = wordValue("Buster") // 85
let busterWordValueString = wordValue("Buster").description // "85"

//

extension Character {
    var lowercase: Character { return Character(String(self).lowercaseString) }
    var value: Int { return Array("abcdefghijklmnopqrstuvwxyz".characters).indexOf(lowercase)?.successor() ?? 0 }
}
extension String {
    var wordValue: Int { return Array(characters).map{ $0.value }.reduce(0){ $0 + $1 } }
}

"Abcde".wordValue    // 15