Swift 银行卡号验证

//  Converted to Swift 4 by Swiftify v4.2.40307 - https://objectivec2swift.com/
func checkBankCardNumber(_ cardNumber: String?) -> Bool {
    var oddSum: Int = 0 // 奇数和
    var evenSum: Int = 0 // 偶数和
    var allSum: Int = 0 // 总和
    // 循环加和
    for i in 1...(cardNumber?.count ?? 0) {
        let theNumber = (cardNumber as NSString?)?.substring(with: NSRange(location: (cardNumber?.count ?? 0) - i, length: 1))
        var lastNumber = Int(truncating: theNumber ?? "") ?? 0
        if i % 2 == 0 {
            // 偶数位
            lastNumber *= 2
            if lastNumber > 9 {
                lastNumber -= 9
            }
            evenSum += lastNumber
        } else {
            // 奇数位
            oddSum += lastNumber
        }
    }
    allSum = oddSum + evenSum
    // 是否合法
    if allSum % 10 == 0 {
        return true
    } else {
        return false
    }
}