Scala example source code file (MapLike.scala)

This example Scala source code file (MapLike.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

a, annotation, b, b1, builder, collection, gentraversableonce, map, maplike, mutable, option, parallel, this, use

The MapLike.scala Scala example source code

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


package scala
package collection
package mutable

import generic._
import scala.annotation.migration
import scala.collection.parallel.mutable.ParMap

/** A template trait for mutable maps.
 *  $mapNote
 *  $mapTags
 *  @since   2.8
 *
 * @define mapNote
 *    '''Implementation note:'''
 *    This trait provides most of the operations of a mutable `Map`
 *    independently of its representation. It is typically inherited by
 *    concrete implementations of maps.
 *
 *    To implement a concrete mutable map, you need to provide
 *    implementations of the following methods:
 *    {{{
 *       def get(key: A): Option[B]
 *       def iterator: Iterator[(A, B)]
 *       def += (kv: (A, B)): This
 *       def -= (key: A): This
 *    }}}
 *    If you wish that methods like `take`, `drop`, `filter` also return the same kind of map
 *    you should also override:
 *    {{{
 *       def empty: This
 *    }}}
 *    It is also good idea to override methods `foreach` and
 *    `size` for efficiency.
 */
trait MapLike[A, B, +This <: MapLike[A, B, This] with Map[A, B]]
  extends scala.collection.MapLike[A, B, This]
     with Builder[(A, B), This]
     with Growable[(A, B)]
     with Shrinkable[A]
     with Cloneable[This]
     with Parallelizable[(A, B), ParMap[A, B]]
{ self =>

  /** A common implementation of `newBuilder` for all mutable maps
   *    in terms of `empty`.
   *
   *    Overrides `MapLike` implementation for better efficiency.
   */
  override protected[this] def newBuilder: Builder[(A, B), This] = empty

  protected[this] override def parCombiner = ParMap.newCombiner[A, B]

  /** Adds a new key/value pair to this map and optionally returns previously bound value.
   *  If the map already contains a
   *  mapping for the key, it will be overridden by the new value.
   *
   * @param key    the key to update
   * @param value  the new value
   * @return an option value containing the value associated with the key
   *         before the `put` operation was executed, or `None` if `key`
   *         was not defined in the map before.
   */
  def put(key: A, value: B): Option[B] = {
    val r = get(key)
    update(key, value)
    r
  }

  /** Adds a new key/value pair to this map.
   *  If the map already contains a
   *  mapping for the key, it will be overridden by the new value.
   *
   *  @param key    The key to update
   *  @param value  The new value
   */
  def update(key: A, value: B) { this += ((key, value)) }

  /** Adds a new key/value pair to this map.
   *  If the map already contains a
   *  mapping for the key, it will be overridden by the new value.
   *  @param    kv the key/value pair.
   *  @return   the map itself
   */
  def += (kv: (A, B)): this.type

  /** Creates a new map consisting of all key/value pairs of the current map
   *  plus a new pair of a given key and value.
   *
   *  @param key    The key to add
   *  @param value  The new value
   *  @return       A fresh immutable map with the binding from `key` to
   *                `value` added to this map.
   */
  override def updated[B1 >: B](key: A, value: B1): Map[A, B1] = this + ((key, value))

  /** Creates a new map containing a new key/value mapping and all the key/value mappings
   *  of this map.
   *
   *  Mapping `kv` will override existing mappings from this map with the same key.
   *
   *  @param kv    the key/value mapping to be added
   *  @return      a new map containing mappings of this map and the mapping `kv`.
   */
  @migration("`+` creates a new map. Use `+=` to add an element to this map and return that map itself.", "2.8.0")
  def + [B1 >: B] (kv: (A, B1)): Map[A, B1] = clone().asInstanceOf[Map[A, B1]] += kv

  /** Creates a new map containing two or more key/value mappings and all the key/value
   *  mappings of this map.
   *
   *  Specified mappings will override existing mappings from this map with the same keys.
   *
   *  @param elem1 the first element to add.
   *  @param elem2 the second element to add.
   *  @param elems the remaining elements to add.
   *  @return      a new map containing mappings of this map and two or more specified mappings.
   */
  @migration("`+` creates a new map. Use `+=` to add an element to this map and return that map itself.", "2.8.0")
  override def + [B1 >: B] (elem1: (A, B1), elem2: (A, B1), elems: (A, B1) *): Map[A, B1] =
    clone().asInstanceOf[Map[A, B1]] += elem1 += elem2 ++= elems

  /** Creates a new map containing the key/value mappings provided by the specified traversable object
   *  and all the key/value mappings of this map.
   *
   *  Note that existing mappings from this map with the same key as those in `xs` will be overriden.
   *
   *  @param xs     the traversable object.
   *  @return       a new map containing mappings of this map and those provided by `xs`.
   */
  @migration("`++` creates a new map. Use `++=` to add an element to this map and return that map itself.", "2.8.0")
  override def ++[B1 >: B](xs: GenTraversableOnce[(A, B1)]): Map[A, B1] =
    clone().asInstanceOf[Map[A, B1]] ++= xs.seq

  /** Removes a key from this map, returning the value associated previously
   *  with that key as an option.
   *  @param    key the key to be removed
   *  @return   an option value containing the value associated previously with `key`,
   *            or `None` if `key` was not defined in the map before.
   */
  def remove(key: A): Option[B] = {
    val r = get(key)
    this -= key
    r
  }

  /** Removes a key from this map.
   *  @param    key the key to be removed
   *  @return   the map itself.
   */
  def -= (key: A): this.type

  /** Creates a new map with all the key/value mappings of this map except the key/value mapping
   *  with the specified key.
   *
   *  @param    key the key to be removed
   *  @return   a new map with all the mappings of this map except that with a key `key`.
   */
  @migration("`-` creates a new map. Use `-=` to remove an element from this map and return that map itself.", "2.8.0")
  override def -(key: A): This = clone() -= key

  /** Removes all bindings from the map. After this operation has completed,
   *  the map will be empty.
   */
  def clear() { keysIterator foreach -= }

  /** If given key is already in this map, returns associated value.
   *
   *  Otherwise, computes value from given expression `op`, stores with key
   *  in map and returns that value.
   *  @param  key the key to test
   *  @param  op  the computation yielding the value to associate with `key`, if
   *              `key` is previously unbound.
   *  @return     the value associated with key (either previously or as a result
   *              of executing the method).
   */
  def getOrElseUpdate(key: A, op: => B): B =
    get(key) match {
      case Some(v) => v
      case None => val d = op; this(key) = d; d
    }

  /** Applies a transformation function to all values contained in this map.
   *  The transformation function produces new values from existing keys
   *  associated values.
   *
   * @param f  the transformation to apply
   * @return   the map itself.
   */
  def transform(f: (A, B) => B): this.type = {
    this.iterator foreach {
      case (key, value) => update(key, f(key, value))
    }
    this
  }

  /** Retains only those mappings for which the predicate
   *  `p` returns `true`.
   *
   * @param p  The test predicate
   */
  def retain(p: (A, B) => Boolean): this.type = {
    for ((k, v) <- this.toList) // SI-7269 toList avoids ConcurrentModificationException
      if (!p(k, v)) this -= k

    this
  }

  override def clone(): This = empty ++= repr

  /** The result when this map is used as a builder
   *  @return  the map representation itself.
   */
  def result: This = repr

  /** Creates a new map with all the key/value mappings of this map except mappings with keys
   *  equal to any of the two or more specified keys.
   *
   *  @param elem1 the first element to remove.
   *  @param elem2 the second element to remove.
   *  @param elems the remaining elements to remove.
   *  @return      a new map containing all the mappings of this map except mappings
   *               with a key equal to `elem1`, `elem2` or any of `elems`.
   */
  @migration("`-` creates a new map. Use `-=` to remove an element from this map and return that map itself.", "2.8.0")
  override def -(elem1: A, elem2: A, elems: A*): This =
    clone() -= elem1 -= elem2 --= elems

  /** Creates a new map with all the key/value mappings of this map except mappings with keys
   *  equal to any of those provided by the specified traversable object.
   *
   *  @param xs       the traversable object.
   *  @return         a new map with all the key/value mappings of this map except mappings
   *                  with a key equal to a key from `xs`.
   */
  @migration("`--` creates a new map. Use `--=` to remove an element from this map and return that map itself.", "2.8.0")
  override def --(xs: GenTraversableOnce[A]): This = clone() --= xs.seq
}