regex - 如何使用正则表达式替换最后一个单词？

Question

我有一个字符串扩展:

func replaceLastWordWithUsername(_ username: String) -> String {
    let pattern = "@*[A-Za-z0-9]*$"
    do {
        Log.info("Replacing", self, username) 
        let regex = try NSRegularExpression(pattern: pattern, options: NSRegularExpression.Options.caseInsensitive)
        let range = NSMakeRange(0, self.characters.count)
        return regex.stringByReplacingMatches(in: self, options: [], range: range, withTemplate: username )
    } catch {
        return self
    }
}

let oldString = "Hey jess"
let newString = oldString.replaceLastWordWithUsername("@jessica")

newString 现在等于Hey @jessica @jessica。预期结果应该是 Hey @jessica

Answer 1

我认为这是因为* regex operator将会

Match 0 or more times. Match as many times as possible.

这可能会导致它除了末尾的单词之外还匹配“末尾无字符”，从而导致两次替换。

正如@Code Different提到的，如果您使用let pattern = "\\w+$"，它只会在有字符的情况下匹配，从而消除“无字符”匹配。

"Word1 Word2"
        ^some characters and then end
            ^0 characters and then end