scala.collection.MapLike.scala Maven / Gradle / Ivy
/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
package scala
package collection
import generic._
import mutable.{ Builder, MapBuilder }
import scala.annotation.migration
import parallel.ParMap
/** A template trait for maps, which associate keys with values.
*
* $mapNote
* $mapTags
* @since 2.8
*
* @define mapNote
* '''Implementation note:'''
* This trait provides most of the operations of a `Map` independently of its representation.
* It is typically inherited by concrete implementations of maps.
*
* To implement a concrete map, you need to provide implementations of the
* following methods:
* {{{
* def get(key: K): Option[V]
* def iterator: Iterator[(K, V)]
* def + [V1 >: V](kv: (K, V1)): This
* def -(key: K): This
* }}}
* If you wish that methods like `take`, `drop`, `filter` also 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.
*
* @define mapTags
* @tparam K the type of the keys.
* @tparam V the type of associated values.
* @tparam This the type of the map itself.
*
* @author Martin Odersky
*
* @define coll map
* @define Coll Map
* @define willNotTerminateInf
* @define mayNotTerminateInf
*/
trait MapLike[K, +V, +This <: MapLike[K, V, This] with Map[K, V]]
extends PartialFunction[K, V]
with IterableLike[(K, V), This]
with GenMapLike[K, V, This]
with Subtractable[K, This]
with Parallelizable[(K, V), ParMap[K, V]]
{
self =>
/** The empty map of the same type as this map
* @return an empty map of type `This`.
*/
def empty: This
/** A common implementation of `newBuilder` for all maps in terms of `empty`.
* Overridden for mutable maps in `mutable.MapLike`.
*/
override protected[this] def newBuilder: Builder[(K, V), This] = new MapBuilder[K, V, This](empty)
/** Optionally returns the value associated with a key.
*
* @param key the key value
* @return an option value containing the value associated with `key` in this map,
* or `None` if none exists.
*/
def get(key: K): Option[V]
/** Creates a new iterator over all key/value pairs of this map
*
* @return the new iterator
*/
def iterator: Iterator[(K, V)]
/** Adds a key/value pair to this map, returning a new map.
* @param kv the key/value pair
* @tparam V1 the type of the value in the key/value pair.
* @return a new map with the new binding added to this map
*
* @usecase def + (kv: (K, V)): Map[K, V]
* @inheritdoc
*/
def + [V1 >: V] (kv: (K, V1)): Map[K, V1]
/** 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 `key`
*
* @usecase def - (key: K): Map[K, V]
* @inheritdoc
*/
def - (key: K): This
/** Tests whether the map is empty.
*
* @return `true` if the map does not contain any key/value binding, `false` otherwise.
*/
override def isEmpty: Boolean = size == 0
/** Returns the value associated with a key, or a default value if the key is not contained in the map.
* @param key the key.
* @param default a computation that yields a default value in case no binding for `key` is
* found in the map.
* @tparam V1 the result type of the default computation.
* @return the value associated with `key` if it exists,
* otherwise the result of the `default` computation.
*
* @usecase def getOrElse(key: K, default: => V): V
* @inheritdoc
*/
def getOrElse[V1 >: V](key: K, default: => V1): V1 = get(key) match {
case Some(v) => v
case None => default
}
/** Retrieves the value which is associated with the given key. This
* method invokes the `default` method of the map if there is no mapping
* from the given key to a value. Unless overridden, the `default` method throws a
* `NoSuchElementException`.
*
* @param key the key
* @return the value associated with the given key, or the result of the
* map's `default` method, if none exists.
*/
def apply(key: K): V = get(key) match {
case None => default(key)
case Some(value) => value
}
/** Tests whether this map contains a binding for a key.
*
* @param key the key
* @return `true` if there is a binding for `key` in this map, `false` otherwise.
*/
def contains(key: K): Boolean = get(key).isDefined
/** Tests whether this map contains a binding for a key. This method,
* which implements an abstract method of trait `PartialFunction`,
* is equivalent to `contains`.
*
* @param key the key
* @return `true` if there is a binding for `key` in this map, `false` otherwise.
*/
def isDefinedAt(key: K) = contains(key)
override /*PartialFunction*/
def applyOrElse[K1 <: K, V1 >: V](x: K1, default: K1 => V1): V1 =
getOrElse(x, default(x))
/** Collects all keys of this map in a set.
* @return a set containing all keys of this map.
*/
def keySet: Set[K] = new DefaultKeySet
/** The implementation class of the set returned by `keySet`.
*/
@SerialVersionUID(1589106351530299313L)
protected class DefaultKeySet extends AbstractSet[K] with Set[K] with Serializable {
def contains(key : K) = self.contains(key)
def iterator = keysIterator
def + (elem: K): Set[K] = (Set[K]() ++ this + elem).asInstanceOf[Set[K]] // !!! concrete overrides abstract problem
def - (elem: K): Set[K] = (Set[K]() ++ this - elem).asInstanceOf[Set[K]] // !!! concrete overrides abstract problem
override def size = self.size
override def foreach[U](f: K => U) = self.keysIterator foreach f
}
/** Creates an iterator for all keys.
*
* @return an iterator over all keys.
*/
def keysIterator: Iterator[K] = new AbstractIterator[K] {
val iter = self.iterator
def hasNext = iter.hasNext
def next() = iter.next()._1
}
/** Collects all keys of this map in an iterable collection.
*
* @return the keys of this map as an iterable.
*/
@migration("`keys` returns `Iterable[K]` rather than `Iterator[K]`.", "2.8.0")
def keys: Iterable[K] = keySet
/** Collects all values of this map in an iterable collection.
*
* @return the values of this map as an iterable.
*/
@migration("`values` returns `Iterable[V]` rather than `Iterator[V]`.", "2.8.0")
def values: Iterable[V] = new DefaultValuesIterable
/** The implementation class of the iterable returned by `values`.
*/
protected class DefaultValuesIterable extends AbstractIterable[V] with Iterable[V] with Serializable {
def iterator = valuesIterator
override def size = self.size
override def foreach[U](f: V => U) = self.valuesIterator foreach f
}
/** Creates an iterator for all values in this map.
*
* @return an iterator over all values that are associated with some key in this map.
*/
def valuesIterator: Iterator[V] = new AbstractIterator[V] {
val iter = self.iterator
def hasNext = iter.hasNext
def next() = iter.next()._2
}
/** Defines the default value computation for the map,
* returned when a key is not found
* The method implemented here throws an exception,
* but it might be overridden in subclasses.
*
* @param key the given key value for which a binding is missing.
* @throws NoSuchElementException
*/
def default(key: K): V =
throw new NoSuchElementException("key not found: " + key)
protected class FilteredKeys(p: K => Boolean) extends AbstractMap[K, V] with DefaultMap[K, V] {
override def foreach[U](f: ((K, V)) => U): Unit = for (kv <- self) if (p(kv._1)) f(kv)
def iterator = self.iterator.filter(kv => p(kv._1))
override def contains(key: K) = p(key) && self.contains(key)
def get(key: K) = if (!p(key)) None else self.get(key)
}
/** Filters this map by retaining only keys satisfying a predicate.
*
* '''Note''': the predicate must accept any key of type `K`, not just those already
* present in the map, as the predicate is tested before the underlying map is queried.
*
* @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.
*/
def filterKeys(p: K => Boolean): Map[K, V] = new FilteredKeys(p)
protected class MappedValues[W](f: V => W) extends AbstractMap[K, W] with DefaultMap[K, W] {
override def foreach[U](g: ((K, W)) => U): Unit = for ((k, v) <- self) g((k, f(v)))
def iterator = for ((k, v) <- self.iterator) yield (k, f(v))
override def size = self.size
override def contains(key: K) = self.contains(key)
def get(key: K) = self.get(key).map(f)
}
/** 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.
*/
def mapValues[W](f: V => W): Map[K, W] = new MappedValues(f)
// The following 5 operations (updated, two times +, two times ++) should really be
// generic, returning This[V]. We need better covariance support to express that though.
// So right now we do the brute force approach of code duplication.
/** Creates a new map obtained by updating this map with a given key/value pair.
* @param key the key
* @param value the value
* @tparam V1 the type of the added value
* @return A new map with the new key/value mapping added to this map.
*
* @usecase def updated(key: K, value: V): Map[K, V]
* @inheritdoc
*/
def updated [V1 >: V](key: K, value: V1): Map[K, V1] = this + ((key, value))
/** Adds key/value pairs to this map, returning a new map.
*
* This method takes two or more key/value pairs. Another overloaded
* variant of this method handles the case where a single key/value pair is
* added.
* @param kv1 the first key/value pair
* @param kv2 the second key/value pair
* @param kvs the remaining key/value pairs
* @tparam V1 the type of the added values
* @return a new map with the given bindings added to this map
*
* @usecase def + (kvs: (K, V)*): Map[K, V]
* @inheritdoc
* @param kvs the key/value pairs
*/
def + [V1 >: V] (kv1: (K, V1), kv2: (K, V1), kvs: (K, V1) *): Map[K, V1] =
this + kv1 + kv2 ++ kvs
/** Adds all key/value pairs in a traversable collection to this map, returning a new map.
*
* @param xs the collection containing the added key/value pairs
* @tparam V1 the type of the added values
* @return a new map with the given bindings added to this map
*
* @usecase def ++ (xs: Traversable[(K, V)]): Map[K, V]
* @inheritdoc
*/
def ++[V1 >: V](xs: GenTraversableOnce[(K, V1)]): Map[K, V1] =
((repr: Map[K, V1]) /: xs.seq) (_ + _)
/** Returns a new map obtained by removing all key/value pairs for which the predicate
* `p` returns `true`.
*
* '''Note:''' This method works by successively removing elements for which the
* predicate is true from this set.
* If removal is slow, or you expect that most elements of the set
* will be removed, you might consider using `filter`
* with a negated predicate instead.
* @param p A predicate over key-value pairs
* @return A new map containing elements not satisfying the predicate.
*/
override def filterNot(p: ((K, V)) => Boolean): This = {
var res: This = repr
for (kv <- this)
if (p(kv)) res = (res - kv._1).asInstanceOf[This] // !!! concrete overrides abstract problem
res
}
override def toSeq: Seq[(K, V)] = {
if (isEmpty) Vector.empty[(K, V)]
else {
// Default appropriate for immutable collections; mutable collections override this
val vb = Vector.newBuilder[(K, V)]
foreach(vb += _)
vb.result
}
}
override def toBuffer[E >: (K, V)]: mutable.Buffer[E] = {
val result = new mutable.ArrayBuffer[E](size)
// Faster to let the map iterate itself than to defer through copyToBuffer
foreach(result += _)
result
}
protected[this] override def parCombiner = ParMap.newCombiner[K, V]
/** Appends all bindings of this map to a string builder using start, end, and separator strings.
* The written text begins with the string `start` and ends with the string
* `end`. Inside, the string representations of all bindings of this map
* in the form of `key -> value` are separated by the string `sep`.
*
* @param b the builder to which strings are appended.
* @param start the starting string.
* @param sep the separator string.
* @param end the ending string.
* @return the string builder `b` to which elements were appended.
*/
override def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder =
this.iterator.map { case (k, v) => k+" -> "+v }.addString(b, start, sep, end)
/** Defines the prefix of this object's `toString` representation.
* @return a string representation which starts the result of `toString` applied to this $coll.
* Unless overridden in subclasses, the string prefix of every map is `"Map"`.
*/
override def stringPrefix: String = "Map"
override /*PartialFunction*/
def toString = super[IterableLike].toString
}
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