问题描述
(注意:标题似乎不清楚-如果有人可以改写我的意思，就是这样！)
(Note: Title doesn't seem to clear -- if someone can rephrase this I'm all for it!)
鉴于此正则表达式:(.*_e\.txt)(与某些文件名匹配)，除了e外，我还需要添加一些其他单字符后缀.我应该选择字符类还是为此使用替代字符? (还是真的很重要吗?)
Given this regex: (.*_e\.txt), which matches some filenames, I need to add some other single character suffixes in addition to the e. Should I choose a character class or should I use an alternation for this? (Or does it really matter??)
也就是说，以下两个中的哪一个看起来更好"，以及原因:
That is, which of the following two seems "better", and why:
a)(.*(e|f|x)\.txt)或
b)(.*[efx]\.txt)
推荐答案
使用[efx]-这正是字符类的设计目的:匹配其中一个字符.因此，它也是最易读和最短的解决方案.
Use [efx] - that's exactly what character classes are designed for: to match one of the included characters. Therefore it's also the most readable and shortest solution.
我不知道它是否更快，但是如果不是更快的话，我会感到非常惊讶.绝对不会慢.
I don't know if it's faster, but I would be very much surprised if it wasn't. It definitely won't be slower.
我的推理(从来没有编写过正则表达式引擎，所以这纯粹是推测):
My reasoning (without ever having written a regex engine, so this is pure conjecture):
正则表达式令牌[abc]将在正则表达式引擎的单个步骤中应用:下一个字符是a，b还是c之一?"
The regex token [abc] will be applied in a single step of the regex engine: "Is the next character one of a, b, or c?"
(a|b|c)但是告诉正则表达式引擎
(a|b|c) however tells the regex engine to
- 记住字符串中的当前位置以进行回溯
- 检查是否可以匹配
a.如果是这样，那就成功了.如果没有: - 检查是否可以匹配
b.如果是这样，那就成功了.如果没有: - 检查是否可以匹配
c.如果是这样，那就成功了.如果没有: - 放弃.
- remember the current position in the string for backtracking, if necessary
- check if it's possible to match
a. If so, success. If not: - check if it's possible to match
b. If so, success. If not: - check if it's possible to match
c. If so, success. If not: - give up.
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