regex - 如何转换使用 Lookahead 的正则表达式模式？

Question

我无法将此正则表达式转换为 Golang 支持的内容。我能得到一些帮助吗？它最初来自 this SO question .

^(?=.{1,24}$)(?![_.])(?!.*[_.]{2})[a-zA-Z0-9._]+(?<![_.])$

标准如下:

1. Only contains alphanumeric characters, underscore and dot.
2. Underscore and dot can't be at the end or start of a username (e.g _username / username_ / .username / username.).
3. Underscore and dot can't be next to each other (e.g user_.name).
4. Underscore or dot can't be used multiple times in a row (e.g user__name / user..name).

Answer 1

我没有任何使用 Go 的经验，所以也许有人可以想出更好的解决方案。
这是我找到的两个选项:

1。编写一个涵盖所有内容的正则表达式除了长度限制

你可以这样使用:

^(?:[a-zA-Z0-9]+[._]?[a-zA-Z0-9]+)+$

Regex101 demo .

你可以使用 len检查字符串长度。这是一个完整的例子:

func main() { 
    var re = regexp.MustCompile(`(?m)^(?:[a-zA-Z0-9]+[._]?[a-zA-Z0-9]+)+$`)
    var str = `username
user_name
user.name
user.name_123
username$$$
_username
username_
user_.name
user._name
user__name
user..name
VeryLongUserNameThatExceedsTheLimit
`
    for i, match := range re.FindAllString(str, -1) {
        if len(match) <= 24 {fmt.Println(match, "found at index", i)}
    }
}

输出:

username found at index 0
user_name found at index 1
user.name found at index 2
user.name_123 found at index 3

Test it online .

---

2。使用第三方引擎

我找到了 this .NET-based engine应该支持 Lookarounds。如果以前的解决方案不适合你，你可以看看这个。请注意，该引擎的作者建议尽可能使用内置引擎:

You'll likely be better off with the RE2 engine from the regexp package and should only use this if you need to write very complex patterns or require compatibility with .NET.