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Scala example source code file (TwoWayCache.scala)

This example Scala source code file (TwoWayCache.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

collection, j, mutable, none, option, s, some, someref, twowaycache, weakhashmap, weakreference

The TwoWayCache.scala Scala example source code

package scala
package reflect
package runtime

import scala.collection.mutable.WeakHashMap
import java.lang.ref.WeakReference

/** A cache that maintains a bijection between Java reflection type `J`
 *  and Scala reflection type `S`.
 *  The cache is two-way weak (i.e. is powered by weak references),
 *  so that neither Java artifacts prevent Scala artifacts from being garbage collected,
 *  nor the other way around.
private[runtime] class TwoWayCache[J, S] {

  private val toScalaMap = new WeakHashMap[J, WeakReference[S]]
  private val toJavaMap = new WeakHashMap[S, WeakReference[J]]

  def enter(j: J, s: S) = synchronized {
    // debugInfo("cached: "+j+"/"+s)
    toScalaMap(j) = new WeakReference(s)
    toJavaMap(s) = new WeakReference(j)

  private object SomeRef {
    def unapply[T](optRef: Option[WeakReference[T]]): Option[T] =
      if (optRef.nonEmpty) {
        val result = optRef.get.get
        if (result != null) Some(result) else None
      } else None

  def toScala(key: J)(body: => S): S = synchronized {
    toScalaMap get key match {
      case SomeRef(v) =>
      case _ =>
        val result = body
        enter(key, result)

  def toJava(key: S)(body: => J): J = synchronized {
    toJavaMap get key match {
      case SomeRef(v) =>
      case _ =>
        val result = body
        enter(result, key)

Other Scala source code examples

Here is a short list of links related to this Scala TwoWayCache.scala source code file:

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