swift - 从 do-catch 语句返回字符串

Question

我试图将代码从 swift 2 转换为 swift 4 并遇到了这个错误

Errors thrown from here are not handled

所以我这样做了，但现在它告诉我返回一个字符串。知道如何做到这一点吗？

func formatSentence(sentence:String) -> String
{
    do {
        let regex = try NSRegularExpression(pattern: "\\W+", options: .caseInsensitive)
        let modifiedString = regex.stringByReplacingMatches(in: sentence, options: [], range: NSRange(location: 0,length: sentence.count), withTemplate: "")

    } catch {
        print(error)
    }

    //I tried adding it here the return modifiedString but gives me error
}

这是原始函数的样子

func formatSentence(sentence:String) -> String
{
    let regex = NSRegularExpression(pattern: "\\W+", options: .caseInsensitive)//NSRegularExpression(pattern:"\\W+", options: .CaseInsensitive, error: nil)
    let modifiedString = regex.stringByReplacingMatches(in: sentence, options: [], range: NSRange(location: 0,length: sentence.count), withTemplate: "")

    return modifiedString
}

Answer 1

这取决于您希望如何处理错误情况。有几个选项:

你可以让它返回 String? ，其中 nil表示有错误:

func formatSentence(_ sentence: String) -> String? {
    do {
        let regex = try NSRegularExpression(pattern: "\\W+", options: .caseInsensitive)
        let range = NSRange(sentence.startIndex..., in: sentence)
        return regex.stringByReplacingMatches(in: sentence, range: range, withTemplate: "")
    } catch {
        print(error)
        return nil
    }
}

然后你会做这样的事情:

guard let sentence = formatSentence(string) else { 
    // handle error here
    return
}

// use `sentence` here

您可以将函数定义为 throws如果遇到一个错误:

func formatSentence(_ sentence: String) throws -> String {
    let regex = try NSRegularExpression(pattern: "\\W+", options: .caseInsensitive)
    let range = NSRange(sentence.startIndex..., in: sentence)
    return regex.stringByReplacingMatches(in: sentence, range: range, withTemplate: "")
}

然后你会在调用点捕获错误:

do {
    let sentence = try formatSentence(string)

    // use `sentence` here
} catch {
    // handle error here
    print(error)
}

或者，假设你知道你的模式是有效的，你可以使用 try!知道它不会失败:

func formatSentence(_ sentence: String) -> String {
    let regex = try! NSRegularExpression(pattern: "\\W+", options: .caseInsensitive)
    let range = NSRange(sentence.startIndex..., in: sentence)
    return regex.stringByReplacingMatches(in: sentence, range: range, withTemplate: "")
}

然后你可以这样做:

let sentence = formatSentence(string)

只有当您以 100% 的置信度知道 NSRegularExpression 时，才使用最后一个模式。鉴于您的正则表达式模式(例如在这种情况下)，不会失败。

顺便说一句，你可以解开戈尔迪之结，然后使用 replacingOccurrences与 .regularExpression选项:

func formatSentence(_ sentence: String) -> String {
    return sentence.replacingOccurrences(of: "\\W+", with: "", options: .regularExpression)
}