Scala中有诸如双向地图之类的东西吗? [英] Is there such a thing as bidirectional maps in Scala?

问题描述

我想链接2列唯一标识符，并且能够通过第二列值获得第一列值，并且能够通过第一列值获得第二列值.像

I'd like to link 2 columns of unique identifiers and be able to get a first column value by a second column value as well as a second column value by a first column value. Something like

Map(1 <-> "one", 2 <-> "two", 3 <-> "three")

在Scala中有这样的设施吗?

Is there such a facility in Scala?

实际上，我还需要更多:3列来选择一个三元组中的任何一个，而另一个则是三元组中的一个(在整个地图中，单个值永远不会满足一次).但是两栏双向地图也可以提供帮助.

Actually I need even more: 3 columns to select any in a triplet by another in a triplet (individual values will never be met more than once in the entire map). But a 2-column bidirectional map can help too.

推荐答案

我的BiMap方法:

object BiMap {
  private[BiMap] trait MethodDistinctor
  implicit object MethodDistinctor extends MethodDistinctor
}

case class BiMap[X, Y](map: Map[X, Y]) {
  def this(tuples: (X,Y)*) = this(tuples.toMap)
  private val reverseMap = map map (_.swap)
  require(map.size == reverseMap.size, "no 1 to 1 relation")
  def apply(x: X): Y = map(x)
  def apply(y: Y)(implicit d: BiMap.MethodDistinctor): X = reverseMap(y)
  val domain = map.keys
  val codomain = reverseMap.keys
}

val biMap = new BiMap(1 -> "A", 2 -> "B")
println(biMap(1)) // A
println(biMap("B")) // 2

当然可以为<->而不是->添加语法.

Of course one can add syntax for <-> instead of ->.

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