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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2007, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */

// $Id$


package scala.collection

import Predef._

object Map {
  trait Projection[A, +B] extends Iterable.Projection[(A,B)] with Map[A,B];
}


/** <p>
* A map is a collection that maps each key to one or zero values.
* </p>
* <p>
* This trait provides a limited interface, only allowing reading of elements.
* There are two extensions of this trait, in packages
* <code><a href="mutable$content.html" target="contentFrame">
* scala.collection.mutable</a></code>
* and <code><a href="immutable$content.html" target="contentFrame">
* scala.collection.immutable</a></code>, which provide functionality for
* adding new key/value mappings to a map. The trait in the first package is
* for maps that are modified destructively, whereas the trait in
* the second package is for immutable maps which create a new map
* when something is added or removed from them.
* </p>
*
* @author Matthias Zenger
* @author Martin Odersky
* @version 1.2, 31/12/2006
*/
trait Map[A, +B] extends PartialFunction[A, B] with Collection[(A, B)] {

  /** Compute the number of key-to-value mappings.
*
* @return the number of mappings
*/
  def size: Int

  /** Check if this map maps <code>key</code> to a value and return the
* value if it exists.
*
* @param key the key of the mapping of interest
* @return the value of the mapping, if it exists
*/
  def get(key: A): Option[B]

  /** Check if this map maps <code>key</code> to a value.
* Return that value if it exists, otherwise return <code>default</code>.
*/
  def getOrElse[B2 >: B](key: A, default: =>B2): B2 =
    get(key) match {
      case Some(v) => v
      case None => default
    }

  /** Is this an empty map?
*
* @return <code>true</code> iff the map is empty.
*/
  override def isEmpty: Boolean = size == 0

  /** Retrieve the value which is associated with the given key. This
* method throws an exception if there is no mapping from the given
* key to a value.
*
* @param key the key
* @return the value associated with the given key.
*/
  def apply(key: A): B = get(key) match {
    case None => default(key)
    case Some(value) => value
  }

  /** Is the given key mapped to a value by this map?
*
* @param key the key
* @return <code>true</code> iff there is a mapping for key in this map
*/
  def contains(key: A): Boolean = get(key) match {
    case None => false
    case Some(_) => true
  }

  /** Does this map contain a mapping from the given key to a value?
*
* @param key the key
* @return <code>true</code> iff there is a mapping for key in this map
*/
  def isDefinedAt(key: A) = contains(key)

  /** Creates an iterator for all keys.
*
* @return an iterator over all keys.
*/
  def keys: Iterator[A] = new Iterator[A] {
    val iter = Map.this.elements
    def hasNext = iter.hasNext
    def next = iter.next._1
  }

  /** @return the keys of this map as a set.
*/
  def keySet: Set[A] = new Set[A] {
    def size = Map.this.size
    def contains(key : A) = Map.this.contains(key)
    def elements = Map.this.elements.map(_._1)
  }

  /** Creates an iterator for a contained values.
*
* @return an iterator over all values.
*/
  def values: Iterator[B] = new Iterator[B] {
    val iter = Map.this.elements
    def hasNext = iter.hasNext
    def next = iter.next._2
  }

  /** Compares two maps structurally; i.e. checks if all mappings
* contained in this map are also contained in the other map,
* and vice versa.
*
* @param that the other map
* @return <code>true</code> iff both maps contain exactly the
* same mappings.
*/
  override def equals(that: Any): Boolean = that match {
    case other: Map[a, b] =>
      this.size == other.size && this.elements.forall {
        case (key, value) => other.get(key.asInstanceOf[a]) match {
          case None => false
          case Some(otherval) => value == otherval
        }
      }
    case _ => false
  }

  /** A hash method compatible with <code>equals</code>
*/
  override def hashCode() =
    (0 /: elements) ((hash, kv) => hash + kv.hashCode)


  /** Creates a string representation for this map.
*
* @return a string showing all mappings
*/
  override def toString() =
    elements.toList.map(kv => kv._1 + " -> " + kv._2).mkString("Map(", ", ", ")")

  /** The default value for the map, returned when a key is not found
* The method implemented here yields an error,
* but it might be overridden in subclasses.
*
* @param key the given key value
* @throws Predef.NoSuchElementException
*/
  def default(key: A): B =
    throw new NoSuchElementException("key not found: " + key)

  override def projection : Map.Projection[A,B] = new Map.Projection[A,B] {
    override def elements = Map.this.elements
    override def size = Map.this.size
    override def get(key : A) : Option[B] = Map.this.get(key)
  }
  /** non-strict filter based on keys only */
  def filterKeys(p : A => Boolean) : Map.Projection[A,B] = new Map.Projection[A,B] {
    def elements = Map.this.elements.filter(x => p(x._1))
    def size = {
      var sz = 0
      Map.this.foreach(x => if (p(x._1)) sz = sz + 1)
      sz
    }
    override def contains(key : A) = Map.this.contains(key) && p(key)
    override def get(key : A) = if (!p(key)) None else Map.this.get(key)
  }
  /** non-strict map elements using existing key set */
  def mapElements[C](f : B => C) : Map.Projection[A,C] = new Map.Projection[A,C] {
    def elements = Map.this.elements.map(e => (e._1, f(e._2)))
    def size = Map.this.size
    override def contains(key : A) = Map.this.contains(key)
    override def get(key : A) = Map.this.get(key).map(f)
  }
}
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