从 swift 3.0 中删除的 C 样式语句，successor() 不可用

Question

谁能帮我把这个for循环更新到swift 3.0。帮助表示赞赏。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，“集合移动它们的索引”，请参阅 A New Model for Collections and Indices Swift 进化。特别是，

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

将索引 fromIndex 提高了 2 个字符位置，但仅 如果它符合有效的索引范围，则返回nil 除此以外。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>