[英]Scala regex pattern matching with String Interpolation
From Scala 2.10 we can define new method r using StringContext like this: 在Scala 2.10中,我们可以使用StringContext定义新方法r,如下所示:
implicit class RegexContext(sc: StringContext) {
def r = new Regex(sc.parts.mkString, sc.parts.tail.map(_ => "x"): _*)
}
Then we can easily define regex pattern after case keyword like this: 然后,我们可以在case关键字之后轻松定义正则表达式模式,如下所示:
"123" match {
case r"\d+" => true
case _ => false
}
Which is not clear to me how the implementation inside of the implicit class RegexContext
works 我不清楚这在隐式类
RegexContext
内部的实现是如何工作的
Can someone explain to me the implementation of the method r
, especially sc.parts.tail.map(_ => "x"): _*
? 有人可以向我解释方法
r
的实现,尤其是sc.parts.tail.map(_ => "x"): _*
吗?
The implementation is taken from How to pattern match using regular expression in Scala? 该实现取自如何在Scala中使用正则表达式进行模式匹配?
Those args are group names, not very useful here. 这些参数是组名,在这里不是很有用。
scala 2.13.0-M5> implicit class R(sc: StringContext) { def r = sc.parts.mkString.r }
defined class R
scala 2.13.0-M5> "hello" match { case r"hell.*" => }
Compare: 相比:
scala 2.13.0-M5> implicit class R(sc: StringContext) { def r = sc.parts.mkString("(.*)").r }
defined class R
scala 2.13.0-M5> "hello" match { case r"hell$x" => x }
res5: String = o
The Regex
constructor takes two arguments. Regex
构造函数带有两个参数。
new Regex (regex: String, groupNames: String*)
新的正则表达式 (正则表达式:字符串,组名:字符串*)
The groupNames
parameter is a vararg so it (they) are actually optional and, in this case, it should have been left empty because that groupNames
code is pretty useless. groupNames
参数是一个vararg,因此它(它们)实际上是可选的,在这种情况下,应将其保留为空,因为groupNames
代码几乎没有用。
Let's review what groupNames
is supposed to do. 让我们回顾一下
groupNames
应该做什么。 We'll start without groupNames
. 我们将从没有
groupNames
开始。
val rx = new Regex("~(A(.)C)~") // pattern with 2 groups, no group names
rx.findAllIn("~ABC~").group(0) //res0: String = ~ABC~
rx.findAllIn("~ABC~").group(1) //res1: String = ABC
rx.findAllIn("~ABC~").group(2) //res2: String = B
rx.findAllIn("~ABC~").group(3) //java.lang.IndexOutOfBoundsException: No group 3
And now with groupNames
. 现在有了
groupNames
。
val rx = new Regex("~(A(.)C)~", "x", "y", "z") // 3 groups named
rx.findAllIn("~ABC~").group("x") //res0: String = ABC
rx.findAllIn("~ABC~").group("y") //res1: String = B
rx.findAllIn("~ABC~").group("z") //java.lang.IndexOutOfBoundsException: No group 3
So why is sc.parts.tail.map(_ => "x"): _*
so useless? 那么,为什么
sc.parts.tail.map(_ => "x"): _*
这么没用? First because the number of names created is unrelated to the number of groups in the pattern, but also because it uses the same string, "x"
, for every name it specifies. 首先是因为创建的名称数量与模式中的组数量无关,而且还因为它为指定的每个名称都使用相同的字符串
"x"
。 That name will only be good for the last group named. 该名称仅对最后一个命名的组有用。
val rx = new Regex("~(A(.)C)~", "x", "x") // 2 groups named
rx.findAllIn("~ABC~").group("x") //res0: String = B (i.e. group(2))
...and... ...和...
val rx = new Regex("~(A(.)C)~", "x", "x", "x") // 3 groups named
rx.findAllIn("~ABC~").group("x") //java.lang.IndexOutOfBoundsException: No group 3
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