swift - 尝试从字符串中检索随机字母时出现段错误

Question

我有这个功能:

func getRandomLetter() -> String {
    let len = allPossibleLetters.characters.count
    let r = arc4random_uniform(UInt32(len))
    let index = allPossibleLetters.index (allPossibleLetters.startIndex, offsetBy: r)
    return String(allPossibleLetters[index])
}

但是我在尝试编译时不断收到以下错误:

Command failed due to signal: Segmentation fault: 11

当我将整数硬编码到 offsetBy 参数中时，它工作正常:

let index = allPossibleLetters.index (allPossibleLetters.startIndex, offsetBy: 11)
// returns a letter as expected

知道是什么原因造成的吗？

Answer 1

似乎是传递了错误类型的问题:

let index = allPossibleLetters.index(allPossibleLetters.startIndex, offsetBy: Int(r))

对于这些分段问题，如果您单击该错误，它将带您查看错误详细信息。通常该日志的最后部分是最有趣的。 在你的情况下，它说:

While type-checking expression at RangeText="allPossibleLetters.index(allPossibleLetters.startIndex, offsetBy: r)"