Packages

package root

This is the documentation for the Scala standard library.

Package structure

The scala package contains core types like Int, Float, Array or Option which are accessible in all Scala compilation units without explicit qualification or imports.

Notable packages include:

scala.collection and its sub-packages contain Scala's collections framework
- scala.collection.immutable - Immutable, sequential data-structures such as Vector, List, Range, HashMap or HashSet
- scala.collection.mutable - Mutable, sequential data-structures such as ArrayBuffer, StringBuilder, HashMap or HashSet
- scala.collection.concurrent - Mutable, concurrent data-structures such as TrieMap
- scala.collection.parallel.immutable - Immutable, parallel data-structures such as ParVector, ParRange, ParHashMap or ParHashSet
- scala.collection.parallel.mutable - Mutable, parallel data-structures such as ParArray, ParHashMap, ParTrieMap or ParHashSet
scala.concurrent - Primitives for concurrent programming such as Futures and Promises
scala.io - Input and output operations
scala.math - Basic math functions and additional numeric types like BigInt and BigDecimal
scala.sys - Interaction with other processes and the operating system
scala.util.matching - Regular expressions

Other packages exist. See the complete list on the right.

Additional parts of the standard library are shipped as separate libraries. These include:

scala.reflect - Scala's reflection API (scala-reflect.jar)
scala.xml - XML parsing, manipulation, and serialization (scala-xml.jar)
scala.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)
scala.util.parsing - Parser combinators (scala-parser-combinators.jar)

Automatic imports

Identifiers in the scala package and the scala.Predef object are always in scope by default.

Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example, List is an alias for scala.collection.immutable.List.

Other aliases refer to classes provided by the underlying platform. For example, on the JVM, String is an alias for java.lang.String.

Definition Classes: root

package scala

Core Scala types.

Core Scala types. They are always available without an explicit import.

Definition Classes: root

package collection

Contains the base traits and objects needed to use and extend Scala's collection library.

Guide

A detailed guide for using the collections library is available at http://docs.scala-lang.org/overviews/collections/introduction.html. Developers looking to extend the collections library can find a description of its architecture at http://docs.scala-lang.org/overviews/core/architecture-of-scala-collections.html.

Using Collections

It is convenient to treat all collections as either a scala.collection.Traversable or scala.collection.Iterable, as these traits define the vast majority of operations on a collection.

Collections can, of course, be treated as specifically as needed, and the library is designed to ensure that the methods that transform collections will return a collection of the same type:

scala> val array = Array(1,2,3,4,5,6)
array: Array[Int] = Array(1, 2, 3, 4, 5, 6)

scala> array map { _.toString }
res0: Array[String] = Array(1, 2, 3, 4, 5, 6)

scala> val list = List(1,2,3,4,5,6)
list: List[Int] = List(1, 2, 3, 4, 5, 6)

scala> list map { _.toString }
res1: List[String] = List(1, 2, 3, 4, 5, 6)

Creating Collections

The most common way to create a collection is to use its companion object as a factory. The three most commonly used collections are scala.collection.Seq, scala.collection.immutable.Set, and scala.collection.immutable.Map. They can be used directly as shown below since their companion objects are all available as type aliases in either the scala package or in scala.Predef. New collections are created like this:

scala> val seq = Seq(1,2,3,4,1)
seq: Seq[Int] = List(1, 2, 3, 4, 1)

scala> val set = Set(1,2,3,4,1)
set: scala.collection.immutable.Set[Int] = Set(1, 2, 3, 4)

scala> val map = Map(1 -> "one", 2 -> "two", 3 -> "three", 2 -> "too")
map: scala.collection.immutable.Map[Int,String] = Map(1 -> one, 2 -> too, 3 -> three)

It is also typical to prefer the scala.collection.immutable collections over those in scala.collection.mutable; the types aliased in the scala.Predef object are the immutable versions.

Also note that the collections library was carefully designed to include several implementations of each of the three basic collection types. These implementations have specific performance characteristics which are described in the guide.

The concrete parallel collections also have specific performance characteristics which are described in the parallel collections guide

Converting to and from Java Collections

The scala.collection.JavaConverters object provides a collection of decorators that allow converting between Scala and Java collections using asScala and asJava methods.

Definition Classes: scala

package concurrent

Definition Classes: collection

Map

TrieMap

package convert

Definition Classes: collection

package generic

Definition Classes: collection

package immutable

Definition Classes: collection

package mutable

Definition Classes: collection

package parallel

Package object for parallel collections.

Definition Classes: collection

package script

Definition Classes: collection

scala.collection

concurrent

package concurrent

Ordering

Alphabetic

Visibility

Public
All

Type Members

trait Map[A, B] extends mutable.Map[A, B]
A template trait for mutable maps that allow concurrent access.
A template trait for mutable maps that allow concurrent access.
This is a base trait for all Scala concurrent map implementations. It provides all of the methods a Map does, with the difference that all the changes are atomic. It also describes methods specific to concurrent maps.
Note: The concurrent maps do not accept null for keys or values.
A
the key type of the map
B
the value type of the map

Since
2.8
See also
"Scala's Collection Library overview" section on Concurrent Maps for more information.
final class TrieMap[K, V] extends Map[K, V] with mutable.MapLike[K, V, TrieMap[K, V]] with CustomParallelizable[(K, V), ParTrieMap[K, V]] with Serializable
A concurrent hash-trie or TrieMap is a concurrent thread-safe lock-free implementation of a hash array mapped trie.
A concurrent hash-trie or TrieMap is a concurrent thread-safe lock-free implementation of a hash array mapped trie. It is used to implement the concurrent map abstraction. It has particularly scalable concurrent insert and remove operations and is memory-efficient. It supports O(1), atomic, lock-free snapshots which are used to implement linearizable lock-free size, iterator and clear operations. The cost of evaluating the (lazy) snapshot is distributed across subsequent updates, thus making snapshot evaluation horizontally scalable.
For details, see: http://lampwww.epfl.ch/~prokopec/ctries-snapshot.pdf

Annotations
@SerialVersionUID()
Since
2.10

Value Members

object TrieMap extends MutableMapFactory[TrieMap] with Serializable

Packages

Package structure

Automatic imports

Guide

Using Collections

Creating Collections

Converting to and from Java Collections

concurrent 

package concurrent

Type Members

Value Members

Ungrouped

concurrent