从 swift 3.0 中删除语句的 C 样式，successor() 不可用 [英] C style for statement removed from swift 3.0, successor() is unavailable

问题描述

任何人都可以帮我更新这个 for 循环到 swift 3.0.0 吗?帮助表示赞赏.谢谢！

Can anyone please help me update this for loop to swift 3.0. help appreciated. Thank you!

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)

    }

推荐答案

在 Swift 3 中，Collections move their index"，参见集合和索引的新模型 关于 Swift 进化.尤其是

In Swift 3, "Collections move their index", see A New Model for Collections and Indices on Swift evolution. In particular,

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除此以外.因此循环可以写成

advanced the index fromIndex by 2 character positions, but only if it fits into the valid range of indices, and returns nil otherwise. Therefore the loop can be written as

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>

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