可以在 Scala 中匹配范围吗？
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Can a range be matched in Scala?
提问by Justin Poliey
Is it possible to match a range of values in Scala?
是否可以在 Scala 中匹配一系列值？
For example:
例如：
val t = 5
val m = t match {
0 until 10 => true
_ => false
}
mwould be trueif twas between 0 and 10, but false otherwise. This little bit doesn't work of course, but is there any way to achieve something like it?
m是true，如果t为0和10，但假另有。这一点当然行不通，但是有没有办法实现类似的目标？
回答by Alexander Azarov
Guard using Range:
守卫使用Range：
val m = t match {
case x if 0 until 10 contains x => true
case _ => false
}
回答by Alexey Romanov
You can use guards:
您可以使用警卫：
val m = t match {
case x if (0 <= x && x < 10) => true
case _ => false
}
回答by swartzrock
Here's another way to match using a range:
这是使用范围进行匹配的另一种方法：
val m = t match {
case x if ((0 to 10).contains(x)) => true
case _ => false
}
回答by Wilfred Springer
With these definitions:
有了这些定义：
trait Inspector[-C, -T] {
def contains(collection: C, value: T): Boolean
}
implicit def seqInspector[T, C <: SeqLike[Any, _]] = new Inspector[C, T]{
override def contains(collection: C, value: T): Boolean = collection.contains(value)
}
implicit def setInspector[T, C <: Set[T]] = new Inspector[C, T] {
override def contains(collection: C, value: T): Boolean = collection.contains(value)
}
implicit class MemberOps[T](t: T) {
def in[C](coll: C)(implicit inspector: Inspector[C, T]) =
inspector.contains(coll, t)
}
You can do checks like these:
你可以做这样的检查：
2 in List(1, 2, 4) // true
2 in List("foo", 2) // true
2 in Set("foo", 2) // true
2 in Set(1, 3) // false
2 in Set("foo", "foo") // does not compile
2 in List("foo", "foo") // false (contains on a list is not the same as contains on a set)
2 in (0 to 10) // true
So the code you need would be:
所以你需要的代码是：
val m = x in (0 to 10)
回答by Noam
Another option would be to actually add this to the language using implicits, i added two variations for int and Range
另一种选择是使用隐式将其实际添加到语言中，我为 int 和 Range 添加了两个变体
object ComparisonExt {
implicit class IntComparisonOps(private val x : Int) extends AnyVal {
def between(range: Range) = x >= range.head && x < range.last
def between(from: Int, to: Int) = x >= from && x < to
}
}
object CallSite {
import ComparisonExt._
val t = 5
if (t between(0 until 10)) println("matched")
if (!(20 between(0 until 10))) println("not matched")
if (t between(0, 10)) println("matched")
if (!(20 between(0, 10))) println("not matched")
}
