Scala Standard Library2.12.4 < Back

Packages

package root
This is the documentation for the Scala standard library.
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.
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.
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.
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.
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
Version
2.9
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

DelayedInit

trait DelayedInit extends AnyRef

Classes and objects (but note, not traits) inheriting the DelayedInit marker trait will have their initialization code rewritten as follows: code becomes delayedInit(code).

Initialization code comprises all statements and all value definitions that are executed during initialization.

Example:

trait Helper extends DelayedInit {
  def delayedInit(body: => Unit) = {
    println("dummy text, printed before initialization of C")
    body // evaluates the initialization code of C
  }
}

class C extends Helper {
  println("this is the initialization code of C")
}

object Test extends App {
  val c = new C
}

Should result in the following being printed:

dummy text, printed before initialization of C
this is the initialization code of C

Annotations: @deprecated
Deprecated: (Since version 2.11.0) DelayedInit semantics can be surprising. Support for App will continue. See the release notes for more details: https://github.com/scala/scala/releases/tag/v2.11.0-RC1
Source: DelayedInit.scala
See also: "Delayed Initialization" subsection of the Scala Language Specification (section 5.1)

Linear Supertypes

AnyRef, Any

Known Subclasses

App

Ordering

Alphabetic
By Inheritance

Inherited

DelayedInit
AnyRef
Any

Implicitly

by any2stringadd
by StringFormat
by Ensuring
by ArrowAssoc

Hide All
Show All

Visibility

Public
All

Abstract Value Members

abstract def delayedInit(x: ⇒ Unit): Unit

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
AnyRef → 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
AnyRef → Any
def +(other: String): String

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

Implicit
This member is added by an implicit conversion from DelayedInit to ArrowAssoc[DelayedInit] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()
final def ==(arg0: Any): Boolean
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
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
AnyRef → 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 clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
returns
a copy of the receiver object.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@native() @throws( ... )
Note
not specified by SLS as a member of AnyRef
def ensuring(cond: (DelayedInit) ⇒ Boolean, msg: ⇒ Any): DelayedInit

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

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

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

Implicit
This member is added by an implicit conversion from DelayedInit to Ensuring[DelayedInit] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
final def eq(arg0: AnyRef): Boolean
Tests whether the argument (that) is a reference to the receiver object (this).
Tests whether the argument (that) is a reference to the receiver object (this).
The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:
- It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
- For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
- null.eq(null) returns true.
When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).
returns
true if the argument is a reference to the receiver object; false otherwise.

Definition Classes
AnyRef
def equals(arg0: Any): Boolean
The equality method for reference types.
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
returns
true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any
def finalize(): Unit
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
Note
not specified by SLS as a member of AnyRef
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 DelayedInit to StringFormat[DelayedInit] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()
final 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
AnyRef → Any
Annotations
@native()
def hashCode(): Int
The hashCode method for reference types.
The hashCode method for reference types. See hashCode in scala.Any.
returns
the hash code value for this object.

Definition Classes
AnyRef → Any
Annotations
@native()
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
final def ne(arg0: AnyRef): Boolean
Equivalent to !(this eq that).
Equivalent to !(this eq that).
returns
true if the argument is not a reference to the receiver object; false otherwise.

Definition Classes
AnyRef
final def notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note
not specified by SLS as a member of AnyRef
final def notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note
not specified by SLS as a member of AnyRef
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def toString(): String
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
returns
a String representation of the object.

Definition Classes
AnyRef → Any
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@native() @throws( ... )
def →[B](y: B): (DelayedInit, B)

Implicit
This member is added by an implicit conversion from DelayedInit to ArrowAssoc[DelayedInit] 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

DelayedInit

trait DelayedInit extends AnyRef

Abstract Value Members

Concrete Value Members

Inherited from AnyRef

Inherited from Any

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

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

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

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

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

DelayedInit 

trait DelayedInit extends AnyRef

Abstract Value Members

Concrete Value Members

Inherited from AnyRef

Inherited from Any

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

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

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

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

Ungrouped

DelayedInit