Scala Standard Library2.13.5 < 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 `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) = …
      //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
- #::
- <:<
- =:=
- 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

c

scala

# Unit

###
Companion object Unit

#### abstract final class Unit extends AnyVal

`Unit` is a subtype of scala.AnyVal. There is only one value of type `Unit`, `()`, and it is not represented by any object in the underlying runtime system. A method with return type `Unit` is analogous to a Java method which is declared `void`.

Source
  Unit.scala

Linear Supertypes
AnyVal, Any
Type Hierarchy

Ordering

1. Alphabetic
2. By Inheritance

Inherited

1. Unit
2. AnyVal
3. Any

Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

1. Hide All
2. Show All

Visibility

1. Public
2. Protected

### Value Members

1.  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
2.  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
3.  def +(other: String): String
   Implicit
     This member is added by an implicit conversion from Unit toany2stringadd[Unit] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd
4.  def ->[B](y: B): (Unit, B)
   Implicit
     This member is added by an implicit conversion from Unit toArrowAssoc[Unit] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()
5.  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
6.  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`.

7.  def ensuring(cond: (Unit) => Boolean, msg: => Any): Unit
   Implicit
     This member is added by an implicit conversion from Unit toEnsuring[Unit] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
8.  def ensuring(cond: (Unit) => Boolean): Unit
   Implicit
     This member is added by an implicit conversion from Unit toEnsuring[Unit] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
9.  def ensuring(cond: Boolean, msg: => Any): Unit
   Implicit
     This member is added by an implicit conversion from Unit toEnsuring[Unit] performed by method Ensuring in scala.Predef.
   Definition Classes
     Ensuring
10.  def ensuring(cond: Boolean): Unit
    Implicit
      This member is added by an implicit conversion from Unit toEnsuring[Unit] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring
11.  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
12.  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 Unit toStringFormat[Unit] performed by method StringFormat in scala.Predef.
    Definition Classes
      StringFormat
    Annotations
      @inline()
13.  def getClass(): Class[Unit]

    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
      Unit → AnyVal → Any
14.  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
15.  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
16.  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

### Deprecated Value Members

1.  def →[B](y: B): (Unit, B)
   Implicit
     This member is added by an implicit conversion from Unit toArrowAssoc[Unit] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @deprecated
   Deprecated

     (Since version 2.13.0) Use `->` instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.

### Inherited from AnyVal

### Inherited from Any

### Inherited by implicit conversion any2stringadd fromUnit to any2stringadd[Unit]

### Inherited by implicit conversion StringFormat fromUnit to StringFormat[Unit]

### Inherited by implicit conversion Ensuring fromUnit to Ensuring[Unit]

### Inherited by implicit conversion ArrowAssoc fromUnit to ArrowAssoc[Unit]

### Ungrouped