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Scala example source code file (IntMap.scala)

This example Scala source code file (IntMap.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

annotation, b, bin, collection, generics, int, intmap, intmapiterator, mutable, none, s, some, t, unit

The IntMap.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection
package immutable

import scala.collection.generic.{ CanBuildFrom, BitOperations }
import scala.collection.mutable.{ Builder, MapBuilder }
import scala.annotation.tailrec

/** Utility class for integer maps.
 *  @author David MacIver
 */
private[immutable] object IntMapUtils extends BitOperations.Int {
  def branchMask(i: Int, j: Int) = highestOneBit(i ^ j)

  def join[T](p1: Int, t1: IntMap[T], p2: Int, t2: IntMap[T]): IntMap[T] = {
    val m = branchMask(p1, p2)
    val p = mask(p1, m)
    if (zero(p1, m)) IntMap.Bin(p, m, t1, t2)
    else IntMap.Bin(p, m, t2, t1)
  }

  def bin[T](prefix: Int, mask: Int, left: IntMap[T], right: IntMap[T]): IntMap[T] = (left, right) match {
    case (left, IntMap.Nil) => left
    case (IntMap.Nil, right) => right
    case (left, right) => IntMap.Bin(prefix, mask, left, right)
  }
}

import IntMapUtils._

/** A companion object for integer maps.
 *
 *  @define Coll  `IntMap`
 *  @define mapCanBuildFromInfo
 *    The standard `CanBuildFrom` instance for `$Coll` objects.
 *    The created value is an instance of class `MapCanBuildFrom`.
 *  @since 2.7
 */
object IntMap {
  /** $mapCanBuildFromInfo */
  implicit def canBuildFrom[A, B] = new CanBuildFrom[IntMap[A], (Int, B), IntMap[B]] {
    def apply(from: IntMap[A]): Builder[(Int, B), IntMap[B]] = apply()
    def apply(): Builder[(Int, B), IntMap[B]] = new MapBuilder[Int, B, IntMap[B]](empty[B])
  }

  def empty[T] : IntMap[T]  = IntMap.Nil

  def singleton[T](key: Int, value: T): IntMap[T] = IntMap.Tip(key, value)

  def apply[T](elems: (Int, T)*): IntMap[T] =
    elems.foldLeft(empty[T])((x, y) => x.updated(y._1, y._2))

  private[immutable] case object Nil extends IntMap[Nothing] {
    // Important! Without this equals method in place, an infinite
    // loop from Map.equals => size => pattern-match-on-Nil => equals
    // develops.  Case objects and custom equality don't mix without
    // careful handling.
    override def equals(that : Any) = that match {
      case _: this.type => true
      case _: IntMap[_] => false // The only empty IntMaps are eq Nil
      case _            => super.equals(that)
    }
  }

  private[immutable] case class Tip[+T](key: Int, value: T) extends IntMap[T]{
    def withValue[S](s: S) =
      if (s.asInstanceOf[AnyRef] eq value.asInstanceOf[AnyRef]) this.asInstanceOf[IntMap.Tip[S]]
      else IntMap.Tip(key, s)
  }
  private[immutable] case class Bin[+T](prefix: Int, mask: Int, left: IntMap[T], right: IntMap[T]) extends IntMap[T] {
    def bin[S](left: IntMap[S], right: IntMap[S]): IntMap[S] = {
      if ((this.left eq left) && (this.right eq right)) this.asInstanceOf[IntMap.Bin[S]]
      else IntMap.Bin[S](prefix, mask, left, right)
    }
  }

}

import IntMap._

// Iterator over a non-empty IntMap.
private[immutable] abstract class IntMapIterator[V, T](it: IntMap[V]) extends AbstractIterator[T] {

  // Basically this uses a simple stack to emulate conversion over the tree. However
  // because we know that Ints are at least 32 bits we can have at most 32 IntMap.Bins and
  // one IntMap.Tip sitting on the tree at any point. Therefore we know the maximum stack
  // depth is 33 and
  var index = 0
  var buffer = new Array[AnyRef](33)

  def pop = {
    index -= 1
    buffer(index).asInstanceOf[IntMap[V]]
  }

  def push(x: IntMap[V]) {
    buffer(index) = x.asInstanceOf[AnyRef]
    index += 1
  }
  push(it)

  /**
   * What value do we assign to a tip?
   */
  def valueOf(tip: IntMap.Tip[V]): T

  def hasNext = index != 0
  final def next: T =
    pop match {
      case IntMap.Bin(_,_, t@IntMap.Tip(_, _), right) => {
        push(right)
        valueOf(t)
      }
      case IntMap.Bin(_, _, left, right) => {
        push(right)
        push(left)
        next
      }
      case t@IntMap.Tip(_, _) => valueOf(t)
      // This should never happen. We don't allow IntMap.Nil in subtrees of the IntMap
      // and don't return an IntMapIterator for IntMap.Nil.
      case IntMap.Nil => sys.error("Empty maps not allowed as subtrees")
    }
}

private[immutable] class IntMapEntryIterator[V](it: IntMap[V]) extends IntMapIterator[V, (Int, V)](it) {
  def valueOf(tip: IntMap.Tip[V]) = (tip.key, tip.value)
}

private[immutable] class IntMapValueIterator[V](it: IntMap[V]) extends IntMapIterator[V, V](it) {
  def valueOf(tip: IntMap.Tip[V]) = tip.value
}

private[immutable] class IntMapKeyIterator[V](it: IntMap[V]) extends IntMapIterator[V, Int](it) {
  def valueOf(tip: IntMap.Tip[V]) = tip.key
}

import IntMap._

/** Specialised immutable map structure for integer keys, based on
 *  <a href="http://citeseer.ist.psu.edu/okasaki98fast.html">Fast Mergeable Integer Maps</a>
 *  by Okasaki and Gill. Essentially a trie based on binary digits of the integers.
 *
 *  '''Note:''' This class is as of 2.8 largely superseded by HashMap.
 *
 *  @tparam T    type of the values associated with integer keys.
 *
 *  @since 2.7
 *  @define Coll `immutable.IntMap`
 *  @define coll immutable integer map
 *  @define mayNotTerminateInf
 *  @define willNotTerminateInf
 */
sealed abstract class IntMap[+T] extends AbstractMap[Int, T]
   with Map[Int, T]
   with MapLike[Int, T, IntMap[T]] {

  override def empty: IntMap[T] = IntMap.Nil

  override def toList = {
    val buffer = new scala.collection.mutable.ListBuffer[(Int, T)]
    foreach(buffer += _)
    buffer.toList
  }

  /**
   * Iterator over key, value pairs of the map in unsigned order of the keys.
   *
   * @return an iterator over pairs of integer keys and corresponding values.
   */
  def iterator: Iterator[(Int, T)] = this match {
    case IntMap.Nil => Iterator.empty
    case _ => new IntMapEntryIterator(this)
  }

  /**
   * Loops over the key, value pairs of the map in unsigned order of the keys.
   */
  override final def foreach[U](f: ((Int, T)) =>  U): Unit = this match {
    case IntMap.Bin(_, _, left, right) => { left.foreach(f); right.foreach(f) }
    case IntMap.Tip(key, value) => f((key, value))
    case IntMap.Nil =>
  }

  override def keysIterator: Iterator[Int] = this match {
    case IntMap.Nil => Iterator.empty
    case _ => new IntMapKeyIterator(this)
  }

  /**
   * Loop over the keys of the map. The same as `keys.foreach(f)`, but may
   * be more efficient.
   *
   * @param f The loop body
   */
  final def foreachKey(f: Int => Unit): Unit = this match {
    case IntMap.Bin(_, _, left, right) => { left.foreachKey(f); right.foreachKey(f) }
    case IntMap.Tip(key, _) => f(key)
    case IntMap.Nil =>
  }

  override def valuesIterator: Iterator[T] = this match {
    case IntMap.Nil => Iterator.empty
    case _ => new IntMapValueIterator(this)
  }

  /**
   * Loop over the values of the map. The same as `values.foreach(f)`, but may
   * be more efficient.
   *
   * @param f The loop body
   */
  final def foreachValue(f: T => Unit): Unit = this match {
    case IntMap.Bin(_, _, left, right) => { left.foreachValue(f); right.foreachValue(f) }
    case IntMap.Tip(_, value) => f(value)
    case IntMap.Nil =>
  }

  override def stringPrefix = "IntMap"

  override def isEmpty = this == IntMap.Nil

  override def filter(f: ((Int, T)) => Boolean): IntMap[T] = this match {
    case IntMap.Bin(prefix, mask, left, right) => {
      val (newleft, newright) = (left.filter(f), right.filter(f))
      if ((left eq newleft) && (right eq newright)) this
      else bin(prefix, mask, newleft, newright)
    }
    case IntMap.Tip(key, value) =>
      if (f((key, value))) this
      else IntMap.Nil
    case IntMap.Nil => IntMap.Nil
  }

  def transform[S](f: (Int, T) => S): IntMap[S] = this match {
    case b@IntMap.Bin(prefix, mask, left, right) => b.bin(left.transform(f), right.transform(f))
    case t@IntMap.Tip(key, value) => t.withValue(f(key, value))
    case IntMap.Nil => IntMap.Nil
  }

  final override def size: Int = this match {
    case IntMap.Nil => 0
    case IntMap.Tip(_, _) => 1
    case IntMap.Bin(_, _, left, right) => left.size + right.size
  }

  final def get(key: Int): Option[T] = this match {
    case IntMap.Bin(prefix, mask, left, right) => if (zero(key, mask)) left.get(key) else right.get(key)
    case IntMap.Tip(key2, value) => if (key == key2) Some(value) else None
    case IntMap.Nil => None
  }

  final override def getOrElse[S >: T](key: Int, default: => S): S = this match {
    case IntMap.Nil => default
    case IntMap.Tip(key2, value) => if (key == key2) value else default
    case IntMap.Bin(prefix, mask, left, right) =>
      if (zero(key, mask)) left.getOrElse(key, default) else right.getOrElse(key, default)
  }

  final override def apply(key: Int): T = this match {
    case IntMap.Bin(prefix, mask, left, right) => if (zero(key, mask)) left(key) else right(key)
    case IntMap.Tip(key2, value) => if (key == key2) value else sys.error("Key not found")
    case IntMap.Nil => sys.error("key not found")
  }

  def + [S >: T] (kv: (Int, S)): IntMap[S] = updated(kv._1, kv._2)

  override def updated[S >: T](key: Int, value: S): IntMap[S] = this match {
    case IntMap.Bin(prefix, mask, left, right) =>
      if (!hasMatch(key, prefix, mask)) join(key, IntMap.Tip(key, value), prefix, this)
      else if (zero(key, mask)) IntMap.Bin(prefix, mask, left.updated(key, value), right)
      else IntMap.Bin(prefix, mask, left, right.updated(key, value))
    case IntMap.Tip(key2, value2) =>
      if (key == key2) IntMap.Tip(key, value)
      else join(key, IntMap.Tip(key, value), key2, this)
    case IntMap.Nil => IntMap.Tip(key, value)
  }

  /**
   * Updates the map, using the provided function to resolve conflicts if the key is already present.
   *
   * Equivalent to:
   * {{{
   *   this.get(key) match {
   *     case None => this.update(key, value)
   *     case Some(oldvalue) => this.update(key, f(oldvalue, value)
   *   }
   * }}}
   *
   * @tparam S     The supertype of values in this `LongMap`.
   * @param key    The key to update
   * @param value  The value to use if there is no conflict
   * @param f      The function used to resolve conflicts.
   * @return       The updated map.
   */
  def updateWith[S >: T](key: Int, value: S, f: (T, S) => S): IntMap[S] = this match {
    case IntMap.Bin(prefix, mask, left, right) =>
      if (!hasMatch(key, prefix, mask)) join(key, IntMap.Tip(key, value), prefix, this)
      else if (zero(key, mask)) IntMap.Bin(prefix, mask, left.updateWith(key, value, f), right)
      else IntMap.Bin(prefix, mask, left, right.updateWith(key, value, f))
    case IntMap.Tip(key2, value2) =>
      if (key == key2) IntMap.Tip(key, f(value2, value))
      else join(key, IntMap.Tip(key, value), key2, this)
    case IntMap.Nil => IntMap.Tip(key, value)
  }

  def - (key: Int): IntMap[T] = this match {
    case IntMap.Bin(prefix, mask, left, right) =>
      if (!hasMatch(key, prefix, mask)) this
      else if (zero(key, mask)) bin(prefix, mask, left - key, right)
      else bin(prefix, mask, left, right - key)
    case IntMap.Tip(key2, _) =>
      if (key == key2) IntMap.Nil
      else this
    case IntMap.Nil => IntMap.Nil
  }

  /**
   * A combined transform and filter function. Returns an `IntMap` such that
   * for each `(key, value)` mapping in this map, if `f(key, value) == None`
   * the map contains no mapping for key, and if `f(key, value)`.
   *
   * @tparam S  The type of the values in the resulting `LongMap`.
   * @param f   The transforming function.
   * @return    The modified map.
   */
  def modifyOrRemove[S](f: (Int, T) => Option[S]): IntMap[S] = this match {
    case IntMap.Bin(prefix, mask, left, right) =>
      val newleft = left.modifyOrRemove(f)
      val newright = right.modifyOrRemove(f)
      if ((left eq newleft) && (right eq newright)) this.asInstanceOf[IntMap[S]]
      else bin(prefix, mask, newleft, newright)
    case IntMap.Tip(key, value) => f(key, value) match {
      case None =>
        IntMap.Nil
      case Some(value2) =>
        //hack to preserve sharing
        if (value.asInstanceOf[AnyRef] eq value2.asInstanceOf[AnyRef]) this.asInstanceOf[IntMap[S]]
        else IntMap.Tip(key, value2)
      }
    case IntMap.Nil =>
      IntMap.Nil
  }

  /**
   * Forms a union map with that map, using the combining function to resolve conflicts.
   *
   * @tparam S      The type of values in `that`, a supertype of values in `this`.
   * @param that    The map to form a union with.
   * @param f       The function used to resolve conflicts between two mappings.
   * @return        Union of `this` and `that`, with identical key conflicts resolved using the function `f`.
   */
  def unionWith[S >: T](that: IntMap[S], f: (Int, S, S) => S): IntMap[S] = (this, that) match{
    case (IntMap.Bin(p1, m1, l1, r1), that@(IntMap.Bin(p2, m2, l2, r2))) =>
      if (shorter(m1, m2)) {
        if (!hasMatch(p2, p1, m1)) join[S](p1, this, p2, that) // TODO: remove [S] when SI-5548 is fixed
        else if (zero(p2, m1)) IntMap.Bin(p1, m1, l1.unionWith(that, f), r1)
        else IntMap.Bin(p1, m1, l1, r1.unionWith(that, f))
      } else if (shorter(m2, m1)){
        if (!hasMatch(p1, p2, m2)) join[S](p1, this, p2, that) // TODO: remove [S] when SI-5548 is fixed
        else if (zero(p1, m2)) IntMap.Bin(p2, m2, this.unionWith(l2, f), r2)
        else IntMap.Bin(p2, m2, l2, this.unionWith(r2, f))
      }
      else {
        if (p1 == p2) IntMap.Bin(p1, m1, l1.unionWith(l2,f), r1.unionWith(r2, f))
        else join[S](p1, this, p2, that) // TODO: remove [S] when SI-5548 is fixed
      }
    case (IntMap.Tip(key, value), x) => x.updateWith[S](key, value, (x, y) => f(key, y, x))
    case (x, IntMap.Tip(key, value)) => x.updateWith[S](key, value, (x, y) => f(key, x, y))
    case (IntMap.Nil, x) => x
    case (x, IntMap.Nil) => x
  }

  /**
   * Forms the intersection of these two maps with a combining function. The
   * resulting map is a map that has only keys present in both maps and has
   * values produced from the original mappings by combining them with `f`.
   *
   * @tparam S      The type of values in `that`.
   * @tparam R      The type of values in the resulting `LongMap`.
   * @param that    The map to intersect with.
   * @param f       The combining function.
   * @return        Intersection of `this` and `that`, with values for identical keys produced by function `f`.
   */
  def intersectionWith[S, R](that: IntMap[S], f: (Int, T, S) => R): IntMap[R] = (this, that) match {
    case (IntMap.Bin(p1, m1, l1, r1), that@IntMap.Bin(p2, m2, l2, r2)) =>
      if (shorter(m1, m2)) {
        if (!hasMatch(p2, p1, m1)) IntMap.Nil
        else if (zero(p2, m1)) l1.intersectionWith(that, f)
        else r1.intersectionWith(that, f)
      } else if (m1 == m2) bin(p1, m1, l1.intersectionWith(l2, f), r1.intersectionWith(r2, f))
        else {
        if (!hasMatch(p1, p2, m2)) IntMap.Nil
        else if (zero(p1, m2)) this.intersectionWith(l2, f)
        else this.intersectionWith(r2, f)
      }
    case (IntMap.Tip(key, value), that) => that.get(key) match {
      case None => IntMap.Nil
      case Some(value2) => IntMap.Tip(key, f(key, value, value2))
    }
    case (_, IntMap.Tip(key, value)) => this.get(key) match {
      case None => IntMap.Nil
      case Some(value2) => IntMap.Tip(key, f(key, value2, value))
    }
    case (_, _) => IntMap.Nil
  }

  /**
   * Left biased intersection. Returns the map that has all the same mappings
   * as this but only for keys which are present in the other map.
   *
   * @tparam R      The type of values in `that`.
   * @param that    The map to intersect with.
   * @return        A map with all the keys both in `this` and `that`, mapped to corresponding values from `this`.
   */
  def intersection[R](that: IntMap[R]): IntMap[T] =
    this.intersectionWith(that, (key: Int, value: T, value2: R) => value)

  def ++[S >: T](that: IntMap[S]) =
    this.unionWith[S](that, (key, x, y) => y)

  /**
   * The entry with the lowest key value considered in unsigned order.
   */
  @tailrec
  final def firstKey: Int = this match {
    case Bin(_, _, l, r) => l.firstKey
    case Tip(k, v) => k
    case IntMap.Nil => sys.error("Empty set")
  }

  /**
   * The entry with the highest key value considered in unsigned order.
   */
  @tailrec
  final def lastKey: Int = this match {
    case Bin(_, _, l, r) => r.lastKey
    case Tip(k, v) => k
    case IntMap.Nil => sys.error("Empty set")
  }
}

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