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, b, b1, c, defaultmap, immutabledefaultkeyset, map, maplike, that, this

The MapLike.scala Scala example source code

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

package scala
package collection
package immutable

import generic._
import parallel.immutable.ParMap

/**
 *  A generic template for immutable maps from keys of type `A`
 *  to values of type `B`.
 *  To implement a concrete map, you need to provide implementations of the
 *  following methods (where `This` is the type of the actual map implementation):
 *
 *  {{{
 *    def get(key: A): Option[B]
 *    def iterator: Iterator[(A, B)]
 *    def + [B1 >: B](kv: (A, B)): Map[A, B1]
 *    def - (key: A): This
 *  }}}
 *
 *  If you wish that transformer methods like `take`, `drop`, `filter` 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.
 *
 *  @tparam A     the type of the keys contained in this collection.
 *  @tparam B     the type of the values associated with the keys.
 *  @tparam This  The type of the actual map implementation.
 *
 *  @author  Martin Odersky
 *  @version 2.8
 *  @since   2.8
 *  @define Coll immutable.Map
 *  @define coll immutable map
 */
trait MapLike[A, +B, +This <: MapLike[A, B, This] with Map[A, B]]
  extends scala.collection.MapLike[A, B, This]
     with Parallelizable[(A, B), ParMap[A, B]]
{
self =>

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

  /** A new immutable map containing updating this map with a given key/value mapping.
   *  @param    key the key
   *  @param    value the value
   *  @return   A new map with the new key/value mapping
   */
  override def updated [B1 >: B](key: A, value: B1): immutable.Map[A, B1] = this + ((key, value))

  /** Add a key/value pair to this map, returning a new map.
   *  @param    kv the key/value pair.
   *  @return   A new map with the new binding added to this map.
   */
  def + [B1 >: B] (kv: (A, B1)): immutable.Map[A, B1]

  /** Adds two or more elements to this collection and returns
   *  a new collection.
   *
   *  @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 with the new bindings added to this map.
   */
  override def + [B1 >: B] (elem1: (A, B1), elem2: (A, B1), elems: (A, B1) *): immutable.Map[A, B1] =
    this + elem1 + elem2 ++ elems

  /** Adds a number of elements provided by a traversable object
   *  and returns a new collection with the added elements.
   *
   *  @param xs      the traversable object consisting of key-value pairs.
   *  @return        a new immutable map with the bindings of this map and those from `xs`.
   */
  override def ++[B1 >: B](xs: GenTraversableOnce[(A, B1)]): immutable.Map[A, B1] =
    ((repr: immutable.Map[A, B1]) /: xs.seq) (_ + _)

  /** Filters this map by retaining only keys satisfying a predicate.
   *  @param  p   the predicate used to test keys
   *  @return an immutable map consisting only of those key value pairs of this map where the key satisfies
   *          the predicate `p`. The resulting map wraps the original map without copying any elements.
   */
  override def filterKeys(p: A => Boolean): Map[A, B] = new FilteredKeys(p) with DefaultMap[A, B]

  /** Transforms this map by applying a function to every retrieved value.
   *  @param  f   the function used to transform values of this map.
   *  @return a map view which maps every key of this map
   *          to `f(this(key))`. The resulting map wraps the original map without copying any elements.
   */
  override def mapValues[C](f: B => C): Map[A, C] = new MappedValues(f) with DefaultMap[A, C]

  /** Collects all keys of this map in a set.
   *  @return  a set containing all keys of this map.
   */
  override def keySet: immutable.Set[A] = new ImmutableDefaultKeySet

  protected class ImmutableDefaultKeySet extends super.DefaultKeySet with immutable.Set[A] {
    override def + (elem: A): immutable.Set[A] =
      if (this(elem)) this
      else immutable.Set[A]() ++ this + elem
    override def - (elem: A): immutable.Set[A] =
      if (this(elem)) immutable.Set[A]() ++ this - elem
      else this
  }

  /** This function transforms all the values of mappings contained
   *  in this map with function `f`.
   *
   *  @param f A function over keys and values
   *  @return  the updated map
   */
  def transform[C, That](f: (A, B) => C)(implicit bf: CanBuildFrom[This, (A, C), That]): That = {
    val b = bf(repr)
    for ((key, value) <- this) b += ((key, f(key, value)))
    b.result()
  }
}