Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

199 lines (174 sloc) 6.471 kb
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2008, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
// $Id$
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(stringPrefix + "(", ", ", ")")
/** 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)
}
/** Defines the prefix of this object's <code>toString</code> representation.
*/
override protected def stringPrefix: String = "Map"
}
Jump to Line
Something went wrong with that request. Please try again.