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 annotation

Definition Classes: scala

package beans

Definition Classes: scala

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 compat

Definition Classes: scala

package concurrent

This package object contains primitives for concurrent and parallel programming.

Guide

A more detailed guide to Futures and Promises, including discussion and examples can be found at http://docs.scala-lang.org/overviews/core/futures.html.

Common Imports

When working with Futures, you will often find that importing the whole concurrent package is convenient:

import scala.concurrent._

When using things like Futures, it is often required to have an implicit ExecutionContext in scope. The general advice for these implicits are as follows.

If the code in question is a class or method definition, and no ExecutionContext is available, request one from the caller by adding an implicit parameter list:

def myMethod(myParam: MyType)(implicit ec: ExecutionContext) = …
//Or
class MyClass(myParam: MyType)(implicit ec: ExecutionContext) { … }

This allows the caller of the method, or creator of the instance of the class, to decide which ExecutionContext should be used.

For typical REPL usage and experimentation, importing the global ExecutionContext is often desired.

import scala.concurrent.ExcutionContext.Implicits.global

Specifying Durations

Operations often require a duration to be specified. A duration DSL is available to make defining these easier:

import scala.concurrent.duration._
val d: Duration = 10.seconds

Using Futures For Non-blocking Computation

Basic use of futures is easy with the factory method on Future, which executes a provided function asynchronously, handing you back a future result of that function without blocking the current thread. In order to create the Future you will need either an implicit or explicit ExecutionContext to be provided:

import scala.concurrent._
import ExecutionContext.Implicits.global  // implicit execution context

val firstZebra: Future[Int] = Future {
  val source = scala.io.Source.fromFile("/etc/dictionaries-common/words")
  source.toSeq.indexOfSlice("zebra")
}

Avoid Blocking

Although blocking is possible in order to await results (with a mandatory timeout duration):

import scala.concurrent.duration._
Await.result(firstZebra, 10.seconds)

and although this is sometimes necessary to do, in particular for testing purposes, blocking in general is discouraged when working with Futures and concurrency in order to avoid potential deadlocks and improve performance. Instead, use callbacks or combinators to remain in the future domain:

val animalRange: Future[Int] = for {
  aardvark <- firstAardvark
  zebra <- firstZebra
} yield zebra - aardvark

animalRange.onSuccess {
  case x if x > 500000 => println("It's a long way from Aardvark to Zebra")
}

Definition Classes: scala

package io

Definition Classes: scala

package math

The package object scala.math contains methods for performing basic numeric operations such as elementary exponential, logarithmic, root and trigonometric functions.

All methods forward to java.lang.Math unless otherwise noted.

Definition Classes: scala
See also: java.lang.Math

package ref

Definition Classes: scala

package reflect

Definition Classes: scala

package runtime

Definition Classes: scala

package sys

The package object scala.sys contains methods for reading and altering core aspects of the virtual machine as well as the world outside of it.

Definition Classes: scala
Since: 2.9

package text

Definition Classes: scala

package util

Definition Classes: scala

Any

AnyVal

App

Array

Boolean

Byte

Char

Cloneable

Console

DelayedInit

Double

Dynamic

Enumeration

Equals

FallbackArrayBuilding

Float

Function

Function0

Function1

Function10

Function11

Function12

Function13

Function14

Function15

Function16

Function17

Function18

Function19

Function2

Function20

Function21

Function22

Function3

Function4

Function5

Function6

Function7

Function8

Function9

Immutable

Int

Long

MatchError

Mutable

None

NotImplementedError

NotNull

Nothing

Null

Option

PartialFunction

Predef

Product

Product1

Product10

Product11

Product12

Product13

Product14

Product15

Product16

Product17

Product18

Product19

Product2

Product20

Product21

Product22

Product3

Product4

Product5

Product6

Product7

Product8

Product9

Proxy

Responder

ScalaReflectionException

SerialVersionUID

Serializable

Short

Some

Specializable

StringContext

Symbol

Tuple1

Tuple10

Tuple11

Tuple12

Tuple13

Tuple14

Tuple15

Tuple16

Tuple17

Tuple18

Tuple19

Tuple2

Tuple20

Tuple21

Tuple22

Tuple3

Tuple4

Tuple5

Tuple6

Tuple7

Tuple8

Tuple9

UninitializedError

UninitializedFieldError

Unit

deprecated

deprecatedInheritance

deprecatedName

deprecatedOverriding

inline

language

languageFeature

native

noinline

remote

specialized

throws

transient

unchecked

volatile

scala

Product

trait Product extends Equals

Base trait for all products, which in the standard library include at least scala.Product1 through scala.Product22 and therefore also their subclasses scala.Tuple1 through scala.Tuple22. In addition, all case classes implement Product with synthetically generated methods.

Source: Product.scala
Since: 2.3

Linear Supertypes

Equals, Any

Known Subclasses

None, Option, Product1, Product10, Product11, Product12, Product13, Product14, Product15, Product16, Product17, Product18, Product19, Product2, Product20, Product21, Product22, Product3, Product4, Product5, Product6, Product7, Product8, Product9, ScalaReflectionException, Some, StringContext, Tuple1, Tuple10, Tuple11, Tuple12, Tuple13, Tuple14, Tuple15, Tuple16, Tuple17, Tuple18, Tuple19, Tuple2, Tuple20, Tuple21, Tuple22, Tuple3, Tuple4, Tuple5, Tuple6, Tuple7, Tuple8, Tuple9, UninitializedFieldError, Found, InsertionPoint, ::, List, Nil, ScanLeaf, ScanNode, Deadline, Either, LeftProjection, RightProjection, Failure, Left, Right, Success, Try, Call, Cont, Done, CompositeThrowable, End, Include, Index, NoLo, Remove, Reset, Start, Update, DocBreak, DocCons, DocGroup, DocNest, DocNil, DocText

Ordering

Alphabetic
By Inheritance

Inherited

Product
Equals
Any

Implicitly

by any2stringadd
by StringFormat
by Ensuring
by ArrowAssoc

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Visibility

Public
All

Abstract Value Members

abstract def canEqual(that: Any): Boolean
A method that should be called from every well-designed equals method that is open to be overridden in a subclass.
A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.
that
the value being probed for possible equality
returns
true if this instance can possibly equal that, otherwise false

Definition Classes
Equals
abstract def getClass(): Class[_]
Returns the runtime class representation of the object.
Returns the runtime class representation of the object.
returns
a class object corresponding to the runtime type of the receiver.

Definition Classes
Any
abstract def productArity: Int
The size of this product.
The size of this product.
returns
for a product A(x₁, ..., x_k), returns k
abstract def productElement(n: Int): Any
The n^th element of this product, 0-based.
The n^th element of this product, 0-based. In other words, for a product A(x₁, ..., x_k), returns x_(n+1) where 0 <= n < k.
n
the index of the element to return
returns
the element n elements after the first element

Exceptions thrown

Concrete Value Members

final def !=(arg0: Any): Boolean
Test two objects for inequality.
Test two objects for inequality.
returns
true if !(this == that), false otherwise.

Definition Classes
Any
final def ##(): Int
Equivalent to x.hashCode except for boxed numeric types and null.
Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.
returns
a hash value consistent with ==

Definition Classes
Any
def +(other: String): String

Implicit
This member is added by an implicit conversion from Product to any2stringadd[Product] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd
def ->[B](y: B): (Product, B)

Implicit
This member is added by an implicit conversion from Product to ArrowAssoc[Product] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()
final def ==(arg0: Any): Boolean
Test two objects for equality.
Test two objects for equality. The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
returns
true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
Any
final def asInstanceOf[T0]: T0
Cast the receiver object to be of type T0.
Cast the receiver object to be of type T0.
Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.
returns
the receiver object.

Definition Classes
Any
Exceptions thrown
ClassCastException if the receiver object is not an instance of the erasure of type T0.
def ensuring(cond: (Product) ⇒ Boolean, msg: ⇒ Any): Product

Implicit
This member is added by an implicit conversion from Product to Ensuring[Product] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: (Product) ⇒ Boolean): Product

Implicit
This member is added by an implicit conversion from Product to Ensuring[Product] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean, msg: ⇒ Any): Product

Implicit
This member is added by an implicit conversion from Product to Ensuring[Product] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean): Product

Implicit
This member is added by an implicit conversion from Product to Ensuring[Product] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def equals(arg0: Any): Boolean
Compares the receiver object (this) with the argument object (that) for equivalence.
Compares the receiver object (this) with the argument object (that) for equivalence.
Any implementation of this method should be an equivalence relation:
- It is reflexive: for any instance x of type Any, x.equals(x) should return true.
- It is symmetric: for any instances x and y of type Any, x.equals(y) should return true if and only if y.equals(x) returns true.
- It is transitive: for any instances x, y, and z of type Any if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
If you override this method, you should verify that your implementation remains an equivalence relation. Additionally, when overriding this method it is usually necessary to override hashCode to ensure that objects which are "equal" (o1.equals(o2) returns true) hash to the same scala.Int. (o1.hashCode.equals(o2.hashCode)).
returns
true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
Any
def formatted(fmtstr: String): String
Returns string formatted according to given format string.
Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

Implicit
This member is added by an implicit conversion from Product to StringFormat[Product] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()
def hashCode(): Int
Calculate a hash code value for the object.
Calculate a hash code value for the object.
The default hashing algorithm is platform dependent.
Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)) yet not be equal (o1.equals(o2) returns false). A degenerate implementation could always return 0. However, it is required that if two objects are equal (o1.equals(o2) returns true) that they have identical hash codes (o1.hashCode.equals(o2.hashCode)). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the equals method.
returns
the hash code value for this object.

Definition Classes
Any
final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object is T0.
Test whether the dynamic type of the receiver object is T0.
Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.
returns
true if the receiver object is an instance of erasure of type T0; false otherwise.

Definition Classes
Any
def productIterator: Iterator[Any]
An iterator over all the elements of this product.
An iterator over all the elements of this product.
returns
in the default implementation, an Iterator[Any]
def productPrefix: String
A string used in the toString methods of derived classes.
A string used in the toString methods of derived classes. Implementations may override this method to prepend a string prefix to the result of toString methods.
returns
in the default implementation, the empty string
def toString(): String
Returns a string representation of the object.
Returns a string representation of the object.
The default representation is platform dependent.
returns
a string representation of the object.

Definition Classes
Any
def →[B](y: B): (Product, B)

Implicit
This member is added by an implicit conversion from Product to ArrowAssoc[Product] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc

Packages

Package structure

Automatic imports

Guide

Using Collections

Creating Collections

Converting to and from Java Collections

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

Product

trait Product extends Equals

Abstract Value Members

Concrete Value Members

Inherited from Equals

Inherited from Any

Inherited by implicit conversion any2stringadd from Product to any2stringadd[Product]

Inherited by implicit conversion StringFormat from Product to StringFormat[Product]

Inherited by implicit conversion Ensuring from Product to Ensuring[Product]

Inherited by implicit conversion ArrowAssoc from Product to ArrowAssoc[Product]

Ungrouped

Packages

Package structure

Automatic imports

Guide

Using Collections

Creating Collections

Converting to and from Java Collections

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

Product 

trait Product extends Equals

Abstract Value Members

Concrete Value Members

Inherited from Equals

Inherited from Any

Inherited by implicit conversion any2stringadd from Product to any2stringadd[Product]

Inherited by implicit conversion StringFormat from Product to StringFormat[Product]

Inherited by implicit conversion Ensuring from Product to Ensuring[Product]

Inherited by implicit conversion ArrowAssoc from Product to ArrowAssoc[Product]

Ungrouped

Product