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/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2009, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
// $Id: Map.scala 16884 2009-01-09 16:52:09Z cunei $
package scala.collection.generic
/** A generic template for 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 map in question):
*
* def get(key: A): Option[B]
* def elements: Iterator[(A, B)]
* def + [B1 >: B](kv: (A, B1)): This
* def -(key: A): This
*
* If you wish that 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.
*/
trait MapTemplate[A, +B, +This <: MapTemplate[A, B, This] with Map[A, B]]
extends PartialFunction[A, B]
with IterableTemplate[(A, B), This]
with Subtractable[A, This] {
self =>
def empty: This
/** Is this an empty map?
*
* @return <code>true</code> iff the map is empty.
*/
override def isEmpty: Boolean = size == 0
/** 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[B1 >: B](key: A, default: => B1): B1 = get(key) match {
case Some(v) => v
case None => default
}
/** 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 = self.elements
def hasNext = iter.hasNext
def next = iter.next._1
}
protected class DefaultKeySet extends Set[A] {
def contains(key : A) = self.contains(key)
def elements = self.elements.map(_._1)
def + (elem: A): Set[A] = (Set[A]() ++ this + elem).asInstanceOf[Set[A]] // !!! concrete overrides abstract problem
def - (elem: A): Set[A] = (Set[A]() ++ this - elem).asInstanceOf[Set[A]] // !!! concrete overrides abstract problem
override def size = self.size
override def foreach[B](f: A => B) = for ((k, v) <- self) f(k)
}
/** @return the keys of this map as a set.
*/
def keySet: Set[A] = new DefaultKeySet
/** Creates an iterator for a contained values.
*
* @return an iterator over all values.
*/
def values: Iterator[B] = new Iterator[B] {
val iter = self.elements
def hasNext = iter.hasNext
def next = iter.next._2
}
/** @return the values of this map as a set (can't do this since Set is covariant)
def valueSet: immutable.Set[B] = immutable.Set.empty[B] ++ (self map (_._2))
*/
/** 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)
/** A map view consisting only of those key value pairs where the key satisfies a given
* predicate `p`.
*/
def filterKeys(p: A => Boolean) = new DefaultMap[A, B] {
override def foreach[C](f: ((A, B)) => C): Unit = for (kv <- self) if (p(kv._1)) f(kv)
def elements = self.elements.filter(kv => p(kv._1))
override def contains(key: A) = self.contains(key) && p(key)
def get(key: A) = if (!p(key)) None else self.get(key)
}
/** A map view resulting from applying a given function `f` to each value.
*/
def mapValues[C](f: B => C) = new DefaultMap[A, C] {
override def foreach[D](g: ((A, C)) => D): Unit = for ((k, v) <- self) g((k, f(v)))
def elements = for ((k, v) <- self.elements) yield (k, f(v))
override def size = self.size
override def contains(key: A) = self.contains(key)
def get(key: A) = self.get(key).map(f)
}
/** @deprecated use mapValues instead
*/
@deprecated def mapElements[C](f: B => C) = mapValues(f)
/** 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
*/
def updated [B1 >: B](key: A, value: B1): 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)): 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.
*/
def + [B1 >: B] (elem1: (A, B1), elem2: (A, B1), elems: (A, B1) *): 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 elems the traversable object.
*/
def ++[B1 >: B](elems: Traversable[(A, B1)]): Map[A, B1] =
((thisCollection: Map[A, B1]) /: elems) (_ + _)
/** Adds a number of elements provided by an iterator
* and returns a new collection with the added elements.
*
* @param iter the iterator
*/
def ++[B1 >: B] (iter: Iterator[(A, B1)]): Map[A, B1] =
((thisCollection: Map[A, B1]) /: iter) (_ + _)
/** Removes a key from this map, returning a new map
* @param key the key to be removed
* @return A new map without a binding for <code>key</code>
*/
def - (key: A): This
/** Creates a string representation for this map.
*
* @return a string showing all mappings
*/
override def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder =
elements.map { case (k, v) => k+" -> "+v }.addString(b, start, sep, end)
/** 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] =>
if (this.size == other.size)
try { // can we find a safer way to do this?
this forall {
case (key, value) => other.get(key.asInstanceOf[a]) match {
case None => false
case Some(otherval) => value == otherval
}
}
} catch {
case ex: ClassCastException => false
}
else false
case _ => false
}
/** Defines the prefix of this object's <code>toString</code> representation.
*/
override def stringPrefix: String = "Map"
/** Need to override string, so that it's not the Function1's string that gets mixed in.
*/
override def toString = super[IterableTemplate].toString
}
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