Swift於字串中插入指定文字

舉個例子

信用卡輸入後，UI有可能會是這樣顯示

0000-0000-0000-0000

假設這個應用的UI不是設定四個TextField
那這時，就有必要在指定的範圍內加入指定字串

extension

extension StringProtocol where Self: RangeReplaceableCollection {
    mutating func insert(separator: Self, every count: Int) {
        for i in indices.reversed() where i != startIndex &&
            distance(from: startIndex, to: i) % count == 0 {
                insert(contentsOf: separator, at: i)
        }
    }
}

使用

var creditcard: String = "1111222233334444"
creditcard.insert(separator: "-", every: 4)
print(creditcard)
//1111-2222-3333-4444