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.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.collection.parallel - Parallel collections (scala-parallel-collections.jar)
- scala.util.parsing - Parser combinators (scala-parser-combinators.jar)
- scala.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.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

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 https://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 Future s, 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) = …
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 words = Files.readAllLines("/etc/dictionaries-common/words").asScala
  words.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 jdk
The jdk package contains utilities to interact with JDK classes.
The jdk package contains utilities to interact with JDK classes.

This packages offers a number of converters, that are able to wrap or copy types from the scala library to equivalent types in the JDK class library and vice versa:
- CollectionConverters , converting collections like scala.collection.Seq , scala.collection.Map , scala.collection.Set , scala.collection.mutable.Buffer , scala.collection.Iterator and scala.collection.Iterable to their JDK counterparts
- OptionConverters , converting between Option and java.util.Optional and primitive variations
- StreamConverters , to create JDK Streams from scala collections
- DurationConverters , for conversions between scala scala.concurrent.duration.FiniteDuration and java.time.Duration
- FunctionConverters , from scala Functions to java java.util.function.Function , java.util.function.UnaryOperator , java.util.function.Consumer and java.util.function.Predicate , as well as primitive variations and Bi-variations.
By convention, converters that wrap an object to provide a different interface to the same underlying data structure use .asScala and .asJava extension methods, whereas converters that copy the underlying data structure use .toScala and .toJava.

In the javaapi package, the same converters can be found with a java-friendly interface that don't rely on implicit enrichments.

Additionally, this package offers Accumulator s, capable of efficiently traversing JDK Streams.
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 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
package util

Definition Classes

scala
#::
<:<
=:=
Any
AnyVal
App
Array
Boolean
Byte
Char
Console
DelayedInit
Double
DummyImplicit
Dynamic
Enumeration
Equals
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
Int
Long
MatchError
None
NotImplementedError
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
ScalaReflectionException
SerialVersionUID
Short
Singleton
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
ValueOf
deprecated
deprecatedInheritance
deprecatedName
deprecatedOverriding
inline
language
languageFeature
native
noinline
specialized
throws
transient
unchecked
volatile

scala

Tuple2

final case class Tuple2 [ +T1 , +T2 ] ( _1: T1 , _2: T2 ) extends Product2 [ T1 , T2 ] with Product with Serializable

A tuple of 2 elements; the canonical representation of a scala.Product2 .

_1: Element 1 of this Tuple2
_2: Element 2 of this Tuple2

Source: Tuple2.scala

Linear Supertypes

java.io.Serializable , Product2 [ T1 , T2 ], Product , Equals , AnyRef , Any

Type Hierarchy

Ordering

Alphabetic
By Inheritance

Inherited

Tuple2
Serializable
Product2
Product
Equals
AnyRef
Any

Implicitly

by tuple2ToZippedOps
by any2stringadd
by StringFormat
by Ensuring
by ArrowAssoc

Hide All
Show All

Visibility

Public
Protected

Instance Constructors

new Tuple2 ( _1: T1 , _2: T2 )
Create a new tuple with 2 elements.

Create a new tuple with 2 elements. Note that it is more idiomatic to create a Tuple2 via (t1, t2)

_1

Element 1 of this Tuple2

_2

Element 2 of this Tuple2

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 ( T1 , T2 ) to any2stringadd [( T1 , T2 )] performed by method any2stringadd in scala.Predef .

Definition Classes

any2stringadd
def -> [ B ] ( y: B ) : (( T1 , T2 ), B )

Implicit

This member is added by an implicit conversion from ( T1 , T2 ) to ArrowAssoc [( T1 , T2 )] 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
val _1 : T1
A projection of element 1 of this Product.

A projection of element 1 of this Product.

returns

A projection of element 1.

Definition Classes

Tuple2 → Product2
val _2 : T2
A projection of element 2 of this Product.

A projection of element 2 of this Product.

returns

A projection of element 2.

Definition Classes

Tuple2 → Product2
final def asInstanceOf [ T0 ] : T0
Forces the compiler to treat the receiver object as having type T0 , even though doing so may violate type safety.
Forces the compiler to treat the receiver object as having type T0 , even though doing so may violate type safety.

This method is useful when you believe you have type information the compiler doesn't, and it also isn't possible to check the type at runtime. In such situations, skipping type safety is the only option.

It is platform dependent whether asInstanceOf has any effect at runtime. It might do a runtime type test on the erasure of T0 , insert a conversion (such as boxing/unboxing), fill in a default value, or do nothing at all.

In particular, asInstanceOf is not a type test. It does **not** mean:
```
this match {
 case x: T0 => x
 case _     => throw ClassCastException("...")
```
Use pattern matching or isInstanceOf for type testing instead.

Situations where asInstanceOf is useful:
- when flow analysis fails to deduce T0 automatically
- when down-casting a type parameter or an abstract type member (which cannot be checked at runtime due to type erasure) If there is any doubt and you are able to type test instead, you should do so.
Be careful of using asInstanceOf when T0 is a primitive type. When T0 is primitive, asInstanceOf may insert a conversion instead of a type test. If your intent is to convert, use a toT method ( x.toChar , x.toByte , etc.).
returns

the receiver object.

Definition Classes

Any

Exceptions thrown

ClassCastException if the receiver is not an instance of the erasure of T0 , if that can be checked on this platform
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[ lang ]

Definition Classes

AnyRef

Annotations

@ throws ( classOf[java.lang.CloneNotSupportedException] ) @ native ()

Note

not specified by SLS as a member of AnyRef
def ensuring ( cond: (( T1 , T2 )) => Boolean , msg: => Any ) : ( T1 , T2 )

Implicit

This member is added by an implicit conversion from ( T1 , T2 ) to Ensuring [( T1 , T2 )] performed by method Ensuring in scala.Predef .

Definition Classes

Ensuring
def ensuring ( cond: (( T1 , T2 )) => Boolean ) : ( T1 , T2 )

Implicit

This member is added by an implicit conversion from ( T1 , T2 ) to Ensuring [( T1 , T2 )] performed by method Ensuring in scala.Predef .

Definition Classes

Ensuring
def ensuring ( cond: Boolean , msg: => Any ) : ( T1 , T2 )

Implicit

This member is added by an implicit conversion from ( T1 , T2 ) to Ensuring [( T1 , T2 )] performed by method Ensuring in scala.Predef .

Definition Classes

Ensuring
def ensuring ( cond: Boolean ) : ( T1 , T2 )

Implicit

This member is added by an implicit conversion from ( T1 , T2 ) to Ensuring [( T1 , T2 )] 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 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[ lang ]

Definition Classes

AnyRef

Annotations

@ throws ( classOf[java.lang.Throwable] )

Note

not specified by SLS as a member of AnyRef
final def getClass () : Class [_ <: AnyRef ]
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 ()
final def isInstanceOf [ T0 ] : Boolean
Test whether the dynamic type of the receiver object has the same erasure as T0 .
Test whether the dynamic type of the receiver object has the same erasure as T0 .

Depending on what T0 is, the test is done in one of the below ways:
- T0 is a non-parameterized class type, e.g. BigDecimal : this method returns true if the value of the receiver object is a BigDecimal or a subtype of BigDecimal .
- T0 is a parameterized class type, e.g. List[Int] : this method returns true if the value of the receiver object is some List[X] for any X . For example, List(1, 2, 3).isInstanceOf[List[String]] will return true.
- T0 is some singleton type x.type or literal x : this method returns this.eq(x) . For example, x.isInstanceOf[1] is equivalent to x.eq(1)
- T0 is an intersection X with Y or X & Y: this method is equivalent to x.isInstanceOf[X] && x.isInstanceOf[Y]
- T0 is a union X | Y : this method is equivalent to x.isInstanceOf[X] || x.isInstanceOf[Y]
- T0 is a type parameter or an abstract type member: this method is equivalent to isInstanceOf[U] where U is T0 's upper bound, Any if T0 is unbounded. For example, x.isInstanceOf[A] where A is an unbounded type parameter will return true for any value of x .
This is exactly equivalent to the type pattern _: T0
returns

true if the receiver object is an instance of erasure of type T0 ; false otherwise.

Definition Classes

Any

Note

due to the unexpectedness of List(1, 2, 3).isInstanceOf[List[String]] returning true and x.isInstanceOf[A] where A is a type parameter or abstract member returning true, these forms issue a warning.
 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
 def productArity : Int The arity of this product. The arity of this product. returns 2 Definition Classes Product2 → Product
 def productElement ( n: Int ) : Any Returns the n-th projection of this product if 0 <= n < productArity, otherwise throws an IndexOutOfBoundsException . Returns the n-th projection of this product if 0 <= n < productArity, otherwise throws an IndexOutOfBoundsException . n number of the projection to be returned returns same as ._(n+1) , for example productElement(0) is the same as ._1 . Definition Classes Product2 → Product Annotations @ throws ( clazz = classOf[IndexOutOfBoundsException] ) Exceptions thrown IndexOutOfBoundsException if the n is out of range(n < 0 || n >= 2).
 def productElementNames : Iterator [ String ] An iterator over the names of all the elements of this product. An iterator over the names of all the elements of this product. Definition Classes Product
 def swap : ( T2 , T1 ) Swaps the elements of this Tuple . Swaps the elements of this Tuple . returns a new Tuple where the first element is the second element of this Tuple and the second element is the first element of this Tuple.
 final def synchronized [ T0 ] ( arg0: => T0 ) : T0 Executes the code in body with an exclusive lock on this . Executes the code in body with an exclusive lock on this . returns the result of body 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 Tuple2 → AnyRef → Any
 final def wait () : Unit See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-- . See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-- . Definition Classes AnyRef Annotations @ throws ( classOf[java.lang.InterruptedException] ) Note not specified by SLS as a member of AnyRef
 final def wait ( arg0: Long , arg1: Int ) : Unit See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int- See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-

Packages

Package structure

Automatic imports

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

Tuple2 

final case class Tuple2 [ +T1 , +T2 ] ( _1: T1 , _2: T2 ) extends Product2 [ T1 , T2 ] with Product with Serializable

Instance Constructors

Value Members

Tuple2