使用明确编号的重复而不是问号、星号和加号 [英] Using explicitly numbered repetition instead of question mark, star and plus

问题描述

我见过使用明确编号的重复而不是 ?、* 和 + 的正则表达式模式，即:

I've seen regex patterns that use explicitly numbered repetition instead of ?, * and +, i.e.:

Explicit            Shorthand
(something){0,1}    (something)?
(something){1}      (something)
(something){0,}     (something)*
(something){1,}     (something)+

问题是:

• 这两种形式是否相同?如果您添加占有/不情愿修饰语会怎样?
• 如果它们是相同的，哪一个更地道?更具可读性?只是更好"?

推荐答案

据我所知，它们是相同的.我认为可能有一些引擎不支持编号语法，但我不确定是哪个.我依稀记得几天前关于 SO 的一个问题，其中显式符号在 Notepad++ 中不起作用.

To my knowledge they are identical. I think there maybe a few engines out there that don't support the numbered syntax but I'm not sure which. I vaguely recall a question on SO a few days ago where explicit notation wouldn't work in Notepad++.

我唯一一次使用明确编号的重复是当重复大于 1 时:

The only time I would use explicitly numbered repetition is when the repetition is greater than 1:

• 正好两个:{2}
• 两个或更多:{2,}
• 二到四:{2,4}

我更喜欢这些，尤其是当重复模式超过几个字符时.如果你必须匹配3个数字，有些人喜欢写:\d\d\d，但我更愿意写\d{3}，因为它强调数字涉及的重复.此外，如果该数字需要更改，我只需要将 {3} 更改为 {n} 而不是在我的脑海中重新解析正则表达式或担心搞砸；它需要较少的脑力劳动.

I tend to prefer these especially when the repeated pattern is more than a few characters. If you have to match 3 numbers, some people like to write: \d\d\d but I would rather write \d{3} since it emphasizes the number of repetitions involved. Furthermore, down the road if that number ever needs to change, I only need to change {3} to {n} and not re-parse the regex in my head or worry about messing it up; it requires less mental effort.

如果不满足该标准，我更喜欢速记.使用显式"符号会很快弄乱模式并使其难以阅读.我曾参与过一个项目，其中一些开发人员不太了解正则表达式(这并不是每个人都喜欢的话题)，我看到了很多 {1} 和 {0,1} 出现.一些人会要求我对他们的模式进行代码审查，这时我会建议将这些出现的情况更改为速记符号并节省空间，并且在 IMO 中提高可读性.

If that criteria isn't met, I prefer the shorthand. Using the "explicit" notation quickly clutters up the pattern and makes it hard to read. I've worked on a project where some developers didn't know regex too well (it's not exactly everyone's favorite topic) and I saw a lot of {1} and {0,1} occurrences. A few people would ask me to code review their pattern and that's when I would suggest changing those occurrences to shorthand notation and save space and, IMO, improve readability.

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