从 do-catch 语句返回字符串

Question

我试图将代码从 swift 2 翻译成 swift 4，但遇到了这个错误

Errors thrown from here are not handled

所以我这样做了，但现在它告诉我 return 一个字符串。知道怎么做吗？

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

在函数开头设置默认值，如下所示：

func formatSentence(sentence:String) -> String {
   var regex = ""
   var modifiedString = "" 

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

   } catch {
       print(error)
   }
   return modifiedString
}

Answer 2

这取决于您要如何处理错误情况。有几个选项：

你可以做到returnString?，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
    }
}

然后你会做类似的事情：

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

// use `sentence` here

您可以将您的函数定义为 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: "")
}

然后你会在调用点发现错误：

do {
    let sentence = try formatSentence(string)

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

或者，假设您知道您的模式是有效的，您可以使用 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% 的信心知道 NSRegularExpression 不会因您的正则表达式模式（例如在这种情况下）而失败时，才使用最后一个模式。

顺便说一句，您可能会快刀斩乱麻，只需将 replacingOccurrences 与 .regularExpression 选项一起使用即可：

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

从 do-catch 语句返回字符串

Returning String from a do-catch statement

swift

do-catch