可在范围在斯卡拉相匹配?
-
20-09-2019 - |
题
是否有可能在Scala中匹配的值的范围?
例如:
val t = 5
val m = t match {
0 until 10 => true
_ => false
}
如果m
是0和10,但假之间否则true
将t
。这一点并不当然的工作,但有什么办法来实现类似的东西?
解决方案
员使用Range
:
val m = t match {
case x if 0 until 10 contains x => true
case _ => false
}
其他提示
您可以使用卫士:
val m = t match {
case x if (0 <= x && x < 10) => true
case _ => false
}
下面的另一种方式使用的范围内,以匹配:
val m = t match {
case x if ((0 to 10).contains(x)) => true
case _ => false
}
使用这些定义:
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)
}
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
所以,你需要的代码是:
val m = x in (0 to 10)
另一种选择是实际此添加到使用implicits语言,我添加int和范围内的两个变型
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")
}
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