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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2006, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */

// $Id$


package scala.collection;

/** This class defines the interface of collections that unambiguously map
* keys to values (i.e. a key is mapped to at least one value).
* Class <code>Map</code> may only be used for
* accessing elements from map implementations. Two different extensions
* of class <code>Map</code> in the package <code>scala.collections.mutable</code>
* and <code>scala.collections.immutable</code> provide functionality for
* adding new key/value mappings to a map. The class in the first package is
* implemented by maps that are modified destructively, whereas the class in
* the second package is used by functional map implementations that rely on
* immutable data structures.
*
* @author Matthias Zenger
* @version 1.1, 02/05/2004
*/
trait Map[A, +B] extends AnyRef
      with PartialFunction[A, B]
      with Iterable[Pair[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];

    /** Is this an empty map?
*
* @return true, iff the map is empty.
*/
    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 true, 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 true, 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;
    }

    /** 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;
    }

    /** Executes the given function for all (key, value) pairs
* contained in this map.
*
* @param f the function to execute.
*/
    def foreach(f: (A, B) => Unit) = {
        val iter = elements;
        while (iter.hasNext) {
            val Pair(key, value) = iter.next;
            f(key, value);
        }
    }

    /** Applies the given predicate to all (key, value) mappings
* contained in this map and returns true if this predicate
* yields true for all mappings.
*
* @param p the predicate
* @return true, iff p yields true for all mappings.
*/
    def forall(p: (A, B) => Boolean): Boolean = elements.forall {
        case Pair(key, value) => p(key, value)
    }

    /** Applies the given predicate to all (key, value) mappings
* contained in this map and returns true if there is at least
* one mapping for which this predicate yields true.
*
* @param p the predicate
* @return true, iff there is at least one mapping for which
* p yields true.
*/
    def exists(p: (A, B) => Boolean): Boolean = elements.exists {
        case Pair(key, value) => p(key, value)
    }

    /** Compares two maps structurally; i.e. checks if all mappings
* contained in this map are also contained in the other map,
* and vice versa.
*
* @return true, 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 Pair(key, value) => other.get(key) match {
            case None => false;
            case Some(otherval) => value == otherval;
          }
        }
      case _ => false
    }

    /** Returns the mappings of this map as a list.
*
* @return a list containing all mappings
*/
    def toList: List[Pair[A, B]] = elements.toList;

    /** Creates a string representation for this map.
*
* @return a string showing all mappings
*/
    override def toString() =
        if (size == 0)
            "{}"
        else
            "{" + {
                val iter = elements;
                var res = iter.next.toString();
                while (iter.hasNext) {
                    res = res + ", " + iter.next;
                }
                res;
            } + "}";

    /** 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.
*/
    def default(key: A): B =
      error("key not found: " + key)
}
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