使用 Regex.fromLiteral() 创建的 Regex 到底匹配什么?

问题描述

我用 Regex.fromLiteral(".*") 创建了一个非常简单的匹配所有正则表达式.

I've created a very simple match-all Regex with Regex.fromLiteral(".*").

根据文档:返回指定文字字符串的文字正则表达式."

According to the documentation: "Returns a literal regex for the specified literal string."

但我真的不明白对于指定的文字字符串"应该是什么意思.

But I don't really get what "for the specified literal string" is supposed to mean.

考虑这个例子:

fun main(args: Array<String>) {
    val regex1 = ".*".toRegex()
    val regex2 = Regex.fromLiteral(".*")
    println("regex1 matches abc: " + regex1.matches("abc"))
    println("regex2 matches abc: " + regex2.matches("abc"))
    println("regex2 matches .* : " + regex2.matches(".*"))
}

输出:

regex1 matches abc: true
regex2 matches abc: false
regex2 matches .* : true

很明显(和我的预期相反)，Regex.fromLiteral() 和 String.toRegex() 表现完全不同(我尝试了几十种不同的参数到 regex2.matches() - 唯一返回 true 的是 .*)

so apparently (and contrary to my expectations), Regex.fromLiteral() and String.toRegex() behave completely different (I've tried dozens of different arguments to regex2.matches() - the only one that returned true was .*)

这是否意味着用 Regex.fromLiteral() 创建的正则表达式总是只匹配它创建的确切字符串?

Does this mean that a Regex created with Regex.fromLiteral() always matches only the exact string it was created with?

如果是，那么这种正则表达式有哪些可能的用例?(我想不出任何有用的场景)

If yes, what are possible use cases for such a Regex? (I can't think of any scenario where that would be useful)

推荐答案

是的，它确实创建了一个与 String 中的文字字符匹配的正则表达式.当您尝试匹配将在正则表达式中解释的符号时，这很方便 - 您不必以这种方式转义它们.

Yes, it does indeed create a regex that matches the literal characters in the String. This is handy when you're trying to match symbols that would be interpreted in a regex - you don't have to escape them this way.

例如，如果您要查找包含 .*[](1)?[2] 的字符串，您可以执行以下操作:

For example, if you're looking for strings that contain .*[](1)?[2], you could do the following:

val regex = Regex.fromLiteral(".*[](1)?[2]")

regex.containsMatchIn("foo")                  // false
regex.containsMatchIn("abc.*[](1)?[2]abc")    // true

当然，您几乎可以使用 Regex 执行任何您可以使用的常规 String 方法.

Of course you can do almost anything you can do with a Regex with just regular String methods too.

val literal = ".*[](1)?[2]"
literal == "foo"                       // equality checks
literal in "abc.*[](1)?[2]abc"         // containment checks
"some string".replace(literal, "new")  // replacements

但有时您需要一个 Regex 实例作为参数，因此在这些情况下可以使用 fromLiteral 方法.对于某些用例，这些针对不同输入的不同操作的性能也可能很有趣.

But sometimes you need a Regex instance as a parameter, so the fromLiteral method can be used in those cases. Performance of these different operations for different inputs could also be interesting for some use cases.

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