Scala 中可以匹配范围吗？

Question

Scala 中是否可以匹配一系列值？

例如：

val t = 5
val m = t match {
    0 until 10 => true
    _ => false
}

如果 t 介于 0 和 10 之间，则 m 将为 true，否则为 false。当然，这一点是行不通的，但是有什么办法可以实现这样的目标吗？

Answer 1

使用 Range 进行防护：

val m = t match {
  case x if 0 until 10 contains x => true
  case _ => false
}

Answer 2

您可以使用守卫：

val m = t match {
    case x if (0 <= x && x < 10) => true
    case _ => false
}

Answer 3

通过这些定义：

  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)
  }

您可以执行如下检查：

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

因此您需要的代码是：

val m = x in (0 to 10)

Answer 4

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
}

Answer 5

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 添加了两种变体

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")
}