swift - '子字符串(到 : )' is deprecated: Please use String slicing subscript with a ' partial range upto' operator

Question

如何将以下代码更新到新版本的 swift:

self.areaCodeLael.text! = localNumber.substring(to: localNumber.index(localNumber.startIndex, offsetBy: 3))

我试过关注这篇文章，但我做对了 How can I use String slicing subscripts in Swift 4?

我将我的原始代码调整为 localNumber[..<3]但我得到:

Cannot subscript a value of type 'String' with an index of type 'PartialRangeUpTo'

Answer 1

在这种情况下，我会说 localNumber.prefix(3)。简短而甜美。