ios - 从 swift 3.0 中删除语句的 C 样式，successor() 不可用

Question

任何人都可以帮我将这个 for 循环更新到 swift 3.0.帮助赞赏。谢谢!

for var index = trimmedString.startIndex; index < trimmedString.endIndex; index = index.successor().successor() {

        let byteString = trimmedString.substringWithRange(Range<String.Index>(start: index, end: index.successor().successor()))
        let num = UInt8(byteString.withCString { strtoul($0, nil, 16) })
        data?.appendBytes([num] as [UInt8], length: 1)

    }

Answer 1

在 Swift 3 中，“Collections move their index”，参见 A New Model for Collections and Indices 关于 Swift 的演变。特别是，

let toIndex = string.index(fromIndex, offsetBy: 2, limitedBy: string.endIndex)

将索引 fromIndex 提高 2 个字符位置，但仅如果它适合索引的有效范围，则返回 nil否则。因此循环可以写成

let string = "0123456789abcdef"
let data = NSMutableData()

var fromIndex = string.startIndex
while let toIndex = string.index(fromIndex, offsetBy: 2, limitedBy: string.endIndex) {

    // Extract hex code at position fromIndex ..< toIndex:
    let byteString = string.substring(with: fromIndex..<toIndex)
    var num = UInt8(byteString.withCString { strtoul($0, nil, 16) })
    data.append(&num, length: 1)

    // Advance to next position:
    fromIndex = toIndex
}

print(data) // <01234567 89abcdef>