Scala example source code file (TwoWayCaches.scala)

This example Scala source code file (TwoWayCaches.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 scala-lang.org; 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, reflection, s, some, someref, symboltable, twowaycache, weakhashmap, weakreference

The TwoWayCaches.scala Scala example source code

package scala.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] trait TwoWayCaches { self: SymbolTable =>
  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) = gilSynchronized {
      // 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 = gilSynchronized {
      toScalaMap get key match {
        case SomeRef(v) =>
          v
        case _ =>
          val result = body
          enter(key, result)
          result
      }
    }

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

    def toJavaOption(key: S)(body: => Option[J]): Option[J] = gilSynchronized {
      toJavaMap get key match {
        case SomeRef(v) =>
          Some(v)
        case _ =>
          val result = body
          for (value <- result) enter(value, key)
          result
      }
    }
  }
}