Scala Standard Library2.13.10 < 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.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 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 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 Accumulators, 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
#::
<:<
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Any
AnyVal
App
Array
Boolean
Byte
Char
Console
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Double
DummyImplicit
Dynamic
Enumeration
Equals
Float
Function
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Function1
Function10
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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
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Tuple1
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Tuple7
Tuple8
Tuple9
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deprecatedName
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language
languageFeature
native
noinline
specialized
throws
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unchecked
volatile

PartialFunction

Companion trait PartialFunction

object PartialFunction

A few handy operations which leverage the extra bit of information available in partial functions. Examples:

import PartialFunction._

def strangeConditional(other: Any): Boolean = cond(other) {
  case x: String if x == "abc" || x == "def"  => true
  case x: Int => true
}
def onlyInt(v: Any): Option[Int] = condOpt(v) { case x: Int => x }

Source: PartialFunction.scala

Linear Supertypes

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Type Members

final class ElementWiseExtractor[-A, +B] extends AnyVal

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
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[lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()
Note
not specified by SLS as a member of AnyRef
def cond[A](x: A)(pf: PartialFunction[A, Boolean]): Boolean
A Boolean test that is the result of the given function where defined, and false otherwise.
A Boolean test that is the result of the given function where defined, and false otherwise.
It behaves like a case _ => false were added to the partial function.
x
the value to test
pf
the partial function
returns
true, iff x is in the domain of pf and pf(x) == true.
def condOpt[A, B](x: A)(pf: PartialFunction[A, B]): Option[B]
Apply the function to the given value if defined, and return the result in a Some; otherwise, return None.
Apply the function to the given value if defined, and return the result in a Some; otherwise, return None.
x
the value to test
pf
the PartialFunction[T, U]
returns
Some(pf(x)) if pf isDefinedAt x, None otherwise.
def empty[A, B]: PartialFunction[A, B]
The partial function with empty domain.
The partial function with empty domain. Any attempt to invoke empty partial function leads to throwing scala.MatchError exception.
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: AnyRef): 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[lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable])
Note
not specified by SLS as a member of AnyRef
def fromFunction[A, B](f: (A) => B): PartialFunction[A, B]
Converts an ordinary function to a partial function.
Converts an ordinary function to a partial function. Note that calling isDefinedAt(x) on this partial function will return true for every x.
f
an ordinary function
returns
a partial function which delegates to the ordinary function f
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()
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 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
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
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-
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])
Note
not specified by SLS as a member of AnyRef
final def wait(arg0: Long): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()
Note
not specified by SLS as a member of AnyRef

Packages

Package structure

Automatic imports

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

PartialFunction

Companion trait PartialFunction

object PartialFunction

Type Members

Value Members

Inherited from AnyRef

Inherited from Any

Ungrouped

Packages

Package structure

Automatic imports

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

PartialFunction

Companion trait PartialFunction

object PartialFunction

Type Members

Value Members

Inherited from AnyRef

Inherited from Any

Ungrouped

PartialFunction