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/Scala 2.13 Library

Package scala

package scala

Core Scala types. They are always available without an explicit import.

Source
package.scala
Linear Supertypes
AnyRef, Any

Package Members

package annotation

package beans

package collection

package compat

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")
}

package io

package jdk

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.

See also

java.lang.Math

package ref

package reflect

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.

Since

2.9

package util

Type Members

type ::[A] = scala.collection.immutable.::[A]

sealed abstract class <:<[-From, +To] extends (From) => To with Serializable

An instance of A <:< B witnesses that A is a subtype of B. Requiring an implicit argument of the type A <:< B encodes the generalized constraint A <: B.

To constrain any abstract type T that's in scope in a method's argument list (not just the method's own type parameters) simply add an implicit argument of type T <:< U, where U is the required upper bound; or for lower-bounds, use: L <:< T, where L is the required lower bound.

In case of any confusion over which method goes in what direction, all the "Co" methods (including apply) go from left to right in the type ("with" the type), and all the "Contra" methods go from right to left ("against" the type). E.g., apply turns a From into a To, and substituteContra replaces the Tos in a type with Froms.

In part contributed by Jason Zaugg.

From

a type which is proved a subtype of To

To

a type which is proved a supertype of From

Annotations
@implicitNotFound("Cannot prove that ${From} <:< ${To}.")
Example:

    scala.Option#flatten

    sealed trait Option[+A] {
      // def flatten[B, A <: Option[B]]: Option[B] = ...
      // won't work, since the A in flatten shadows the class-scoped A.
      def flatten[B](implicit ev: A <:< Option[B]): Option[B]
        = if(isEmpty) None else ev(get)
      // Because (A <:< Option[B]) <: (A => Option[B]), ev can be called to turn the
      // A from get into an Option[B], and because ev is implicit, that call can be
      // left out and inserted automatically.
    }
See also

=:= for expressing equality constraints

sealed abstract class =:=[From, To] extends <:<[From, To] with Serializable

An instance of A =:= B witnesses that the types A and B are equal. It also acts as a A <:< B, but not a B <:< A (directly) due to restrictions on subclassing.

In case of any confusion over which method goes in what direction, all the "Co" methods (including apply) go from left to right in the type ("with" the type), and all the "Contra" methods go from right to left ("against" the type). E.g., apply turns a From into a To, and substituteContra replaces the Tos in a type with Froms.

From

a type which is proved equal to To

To

a type which is proved equal to From

Annotations
@implicitNotFound("Cannot prove that ${From} =:= ${To}.")
Example:

    An in-place variant of scala.collection.mutable.ArrayBuffer#transpose

    implicit class BufOps[A](private val buf: ArrayBuffer[A]) extends AnyVal {
      def inPlaceTranspose[E]()(implicit ev: A =:= ArrayBuffer[E]) = ???
      // Because ArrayBuffer is invariant, we can't make do with just a A <:< ArrayBuffer[E]
      // Getting buffers *out* from buf would work, but adding them back *in* wouldn't.
    }
See also

<:< for expressing subtyping constraints

type AbstractMethodError = java.lang.AbstractMethodError

abstract class Any

Class Any is the root of the Scala class hierarchy. Every class in a Scala execution environment inherits directly or indirectly from this class.

Starting with Scala 2.10 it is possible to directly extend Any using universal traits. A universal trait is a trait that extends Any, only has defs as members, and does no initialization.

The main use case for universal traits is to allow basic inheritance of methods for value classes. For example,

trait Printable extends Any {
  def print(): Unit = println(this)
}
class Wrapper(val underlying: Int) extends AnyVal with Printable

val w = new Wrapper(3)
w.print()

See the Value Classes and Universal Traits for more details on the interplay of universal traits and value classes.

abstract class AnyVal extends Any

AnyVal is the root class of all value types, which describe values not implemented as objects in the underlying host system. Value classes are specified in Scala Language Specification, section 12.2.

The standard implementation includes nine AnyVal subtypes:

scala.Double, scala.Float, scala.Long, scala.Int, scala.Char, scala.Short, and scala.Byte are the numeric value types.

scala.Unit and scala.Boolean are the non-numeric value types.

Other groupings:

Prior to Scala 2.10, AnyVal was a sealed trait. Beginning with Scala 2.10, however, it is possible to define a subclass of AnyVal called a user-defined value class which is treated specially by the compiler. Properly-defined user value classes provide a way to improve performance on user-defined types by avoiding object allocation at runtime, and by replacing virtual method invocations with static method invocations.

User-defined value classes which avoid object allocation...

    must have a single val parameter that is the underlying runtime representation.can define defs, but no vals, vars, or nested traitss, classes or objects.typically extend no other trait apart from AnyVal.cannot be used in type tests or pattern matching.may not override equals or hashCode methods.

A minimal example:

class Wrapper(val underlying: Int) extends AnyVal {
  def foo: Wrapper = new Wrapper(underlying * 19)
}

It's important to note that user-defined value classes are limited, and in some circumstances, still must allocate a value class instance at runtime. These limitations and circumstances are explained in greater detail in the Value Classes and Universal Traits.

trait App extends DelayedInit

The App trait can be used to quickly turn objects into executable programs. Here is an example:

object Main extends App {
  Console.println("Hello World: " + (args mkString ", "))
}

No explicit main method is needed. Instead, the whole class body becomes the “main method”.

args returns the current command line arguments as an array.

Caveats

It should be noted that this trait is implemented using the DelayedInit functionality, which means that fields of the object will not have been initialized before the main method has been executed.

Future versions of this trait will no longer extend DelayedInit.

Since

2.1

final class Array[T] extends java.io.Serializable with java.lang.Cloneable

Arrays are mutable, indexed collections of values. Array[T] is Scala's representation for Java's T[].

val numbers = Array(1, 2, 3, 4)
val first = numbers(0) // read the first element
numbers(3) = 100 // replace the 4th array element with 100
val biggerNumbers = numbers.map(_ * 2) // multiply all numbers by two

Arrays make use of two common pieces of Scala syntactic sugar, shown on lines 2 and 3 of the above example code. Line 2 is translated into a call to apply(Int), while line 3 is translated into a call to update(Int, T).

Two implicit conversions exist in scala.Predef that are frequently applied to arrays: a conversion to scala.collection.ArrayOps (shown on line 4 of the example above) and a conversion to scala.collection.mutable.ArraySeq (a subtype of scala.collection.Seq). Both types make available many of the standard operations found in the Scala collections API. The conversion to ArrayOps is temporary, as all operations defined on ArrayOps return an Array, while the conversion to ArraySeq is permanent as all operations return a ArraySeq.

The conversion to ArrayOps takes priority over the conversion to ArraySeq. For instance, consider the following code:

val arr = Array(1, 2, 3)
val arrReversed = arr.reverse
val seqReversed : collection.Seq[Int] = arr.reverse

Value arrReversed will be of type Array[Int], with an implicit conversion to ArrayOps occurring to perform the reverse operation. The value of seqReversed, on the other hand, will be computed by converting to ArraySeq first and invoking the variant of reverse that returns another ArraySeq.

Since

1.0

See also

Scala Language Specification, for in-depth information on the transformations the Scala compiler makes on Arrays (Sections 6.6 and 6.15 respectively.)

"Scala 2.8 Arrays" the Scala Improvement Document detailing arrays since Scala 2.8.

"The Scala 2.8 Collections' API" section on Array by Martin Odersky for more information.

type ArrayIndexOutOfBoundsException = java.lang.ArrayIndexOutOfBoundsException

type BigDecimal = scala.math.BigDecimal

type BigInt = scala.math.BigInt

abstract final class Boolean extends AnyVal

Boolean (equivalent to Java's boolean primitive type) is a subtype of scala.AnyVal. Instances of Boolean are not represented by an object in the underlying runtime system.

There is an implicit conversion from scala.Boolean => scala.runtime.RichBoolean which provides useful non-primitive operations.

abstract final class Byte extends AnyVal

Byte, a 8-bit signed integer (equivalent to Java's byte primitive type) is a subtype of scala.AnyVal. Instances of Byte are not represented by an object in the underlying runtime system.

There is an implicit conversion from scala.Byte => scala.runtime.RichByte which provides useful non-primitive operations.

abstract final class Char extends AnyVal

Char, a 16-bit unsigned integer (equivalent to Java's char primitive type) is a subtype of scala.AnyVal. Instances of Char are not represented by an object in the underlying runtime system.

There is an implicit conversion from scala.Char => scala.runtime.RichChar which provides useful non-primitive operations.

type ClassCastException = java.lang.ClassCastException

type Cloneable = java.lang.Cloneable

abstract final class Double extends AnyVal

Double, a 64-bit IEEE-754 floating point number (equivalent to Java's double primitive type) is a subtype of scala.AnyVal. Instances of Double are not represented by an object in the underlying runtime system.

There is an implicit conversion from scala.Double => scala.runtime.RichDouble which provides useful non-primitive operations.

final class DummyImplicit extends AnyRef

trait Dynamic extends Any

A marker trait that enables dynamic invocations. Instances x of this trait allow method invocations x.meth(args) for arbitrary method names meth and argument lists args as well as field accesses x.field for arbitrary field names field.

If a call is not natively supported by x (i.e. if type checking fails), it is rewritten according to the following rules:

foo.method("blah")      ~~> foo.applyDynamic("method")("blah")
foo.method(x = "blah")  ~~> foo.applyDynamicNamed("method")(("x", "blah"))
foo.method(x = 1, 2)    ~~> foo.applyDynamicNamed("method")(("x", 1), ("", 2))
foo.field           ~~> foo.selectDynamic("field")
foo.varia = 10      ~~> foo.updateDynamic("varia")(10)
foo.arr(10) = 13    ~~> foo.selectDynamic("arr").update(10, 13)
foo.arr(10)         ~~> foo.applyDynamic("arr")(10)

As of Scala 2.10, defining direct or indirect subclasses of this trait is only possible if the language feature dynamics is enabled.

type Either[+A, +B] = scala.util.Either[A, B]

abstract class Enumeration extends Serializable

Defines a finite set of values specific to the enumeration. Typically these values enumerate all possible forms something can take and provide a lightweight alternative to case classes.

Each call to a Value method adds a new unique value to the enumeration. To be accessible, these values are usually defined as val members of the enumeration.

All values in an enumeration share a common, unique type defined as the Value type member of the enumeration (Value selected on the stable identifier path of the enumeration instance).

Values SHOULD NOT be added to an enumeration after its construction; doing so makes the enumeration thread-unsafe. If values are added to an enumeration from multiple threads (in a non-synchronized fashion) after construction, the behavior of the enumeration is undefined.

Annotations
@SerialVersionUID()
Examples:
    // Define a new enumeration with a type alias and work with the full set of enumerated values
    object WeekDay extends Enumeration {
      type WeekDay = Value
      val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
    }
    import WeekDay._
    
    def isWorkingDay(d: WeekDay) = ! (d == Sat || d == Sun)
    
    WeekDay.values filter isWorkingDay foreach println
    // output:
    // Mon
    // Tue
    // Wed
    // Thu
    // Fri
    ,
    // Example of adding attributes to an enumeration by extending the Enumeration.Val class
    object Planet extends Enumeration {
      protected case class Val(mass: Double, radius: Double) extends super.Val {
        def surfaceGravity: Double = Planet.G * mass / (radius * radius)
        def surfaceWeight(otherMass: Double): Double = otherMass * surfaceGravity
      }
      import scala.language.implicitConversions
      implicit def valueToPlanetVal(x: Value): Val = x.asInstanceOf[Val]
    
      val G: Double = 6.67300E-11
      val Mercury = Val(3.303e+23, 2.4397e6)
      val Venus   = Val(4.869e+24, 6.0518e6)
      val Earth   = Val(5.976e+24, 6.37814e6)
      val Mars    = Val(6.421e+23, 3.3972e6)
      val Jupiter = Val(1.9e+27, 7.1492e7)
      val Saturn  = Val(5.688e+26, 6.0268e7)
      val Uranus  = Val(8.686e+25, 2.5559e7)
      val Neptune = Val(1.024e+26, 2.4746e7)
    }
    
    println(Planet.values.filter(_.radius > 7.0e6))
    // output:
    // Planet.ValueSet(Jupiter, Saturn, Uranus, Neptune)

trait Equals extends Any

An interface containing operations for equality. The only method not already present in class AnyRef is canEqual.

type Equiv[T] = scala.math.Equiv[T]

type Error = java.lang.Error

type Exception = java.lang.Exception

abstract final class Float extends AnyVal

Float, a 32-bit IEEE-754 floating point number (equivalent to Java's float primitive type) is a subtype of scala.AnyVal. Instances of Float are not represented by an object in the underlying runtime system.

There is an implicit conversion from scala.Float => scala.runtime.RichFloat which provides useful non-primitive operations.

type Fractional[T] = scala.math.Fractional[T]

trait Function0[+R] extends AnyRef

A function of 0 parameters.

In the following example, the definition of javaVersion is a shorthand for the anonymous class definition anonfun0:

 object Main extends App {
   val javaVersion = () => sys.props("java.version")

   val anonfun0 = new Function0[String] {
     def apply(): String = sys.props("java.version")
   }
   assert(javaVersion() == anonfun0())
}

trait Function1[-T1, +R] extends AnyRef

A function of 1 parameter.

In the following example, the definition of succ is a shorthand for the anonymous class definition anonfun1:

 object Main extends App {
   val succ = (x: Int) => x + 1
   val anonfun1 = new Function1[Int, Int] {
     def apply(x: Int): Int = x + 1
   }
   assert(succ(0) == anonfun1(0))
}

Note that the difference between Function1 and scala.PartialFunction is that the latter can specify inputs which it will not handle.

Annotations
@implicitNotFound("No implicit view available from ${T1} => ${R}.")

trait Function10[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, +R] extends AnyRef

trait Function11[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, +R] extends AnyRef

trait Function12[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, +R] extends AnyRef

trait Function13[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, +R] extends AnyRef

trait Function14[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, +R] extends AnyRef

trait Function15[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, -T15, +R] extends AnyRef

trait Function16[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, -T15, -T16, +R] extends AnyRef

trait Function17[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, -T15, -T16, -T17, +R] extends AnyRef

trait Function18[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, -T15, -T16, -T17, -T18, +R] extends AnyRef

trait Function19[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, -T15, -T16, -T17, -T18, -T19, +R] extends AnyRef

trait Function2[-T1, -T2, +R] extends AnyRef

A function of 2 parameters.

In the following example, the definition of max is a shorthand for the anonymous class definition anonfun2:

 object Main extends App {
   val max = (x: Int, y: Int) => if (x < y) y else x

   val anonfun2 = new Function2[Int, Int, Int] {
     def apply(x: Int, y: Int): Int = if (x < y) y else x
   }
   assert(max(0, 1) == anonfun2(0, 1))
}

trait Function20[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, -T15, -T16, -T17, -T18, -T19, -T20, +R] extends AnyRef

trait Function21[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, -T15, -T16, -T17, -T18, -T19, -T20, -T21, +R] extends AnyRef

trait Function22[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, -T10, -T11, -T12, -T13, -T14, -T15, -T16, -T17, -T18, -T19, -T20, -T21, -T22, +R] extends AnyRef

trait Function3[-T1, -T2, -T3, +R] extends AnyRef

trait Function4[-T1, -T2, -T3, -T4, +R] extends AnyRef

trait Function5[-T1, -T2, -T3, -T4, -T5, +R] extends AnyRef

trait Function6[-T1, -T2, -T3, -T4, -T5, -T6, +R] extends AnyRef

trait Function7[-T1, -T2, -T3, -T4, -T5, -T6, -T7, +R] extends AnyRef

trait Function8[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, +R] extends AnyRef

trait Function9[-T1, -T2, -T3, -T4, -T5, -T6, -T7, -T8, -T9, +R] extends AnyRef

type IllegalArgumentException = java.lang.IllegalArgumentException

type IndexOutOfBoundsException = java.lang.IndexOutOfBoundsException

type IndexedSeq[+A] = scala.collection.immutable.IndexedSeq[A]

Annotations
@migration
Migration

(Changed in version 2.13.0) scala.IndexedSeq is now scala.collection.immutable.IndexedSeq instead of scala.collection.IndexedSeq

abstract final class Int extends AnyVal

Int, a 32-bit signed integer (equivalent to Java's int primitive type) is a subtype of scala.AnyVal. Instances of Int are not represented by an object in the underlying runtime system.

There is an implicit conversion from scala.Int => scala.runtime.RichInt which provides useful non-primitive operations.

type Integral[T] = scala.math.Integral[T]

type InterruptedException = java.lang.InterruptedException

type Iterable[+A] = scala.collection.Iterable[A]

type IterableOnce[+A] = scala.collection.IterableOnce[A]

type Iterator[+A] = scala.collection.Iterator[A]

type LazyList[+A] = scala.collection.immutable.LazyList[A]

type Left[+A, +B] = scala.util.Left[A, B]

type List[+A] = scala.collection.immutable.List[A]

abstract final class Long extends AnyVal

Long, a 64-bit signed integer (equivalent to Java's long primitive type) is a subtype of scala.AnyVal. Instances of Long are not represented by an object in the underlying runtime system.

There is an implicit conversion from scala.Long => scala.runtime.RichLong which provides useful non-primitive operations.

final class MatchError extends RuntimeException

This class implements errors which are thrown whenever an object doesn't match any pattern of a pattern matching expression.

Since

2.0

type NoSuchElementException = java.util.NoSuchElementException

final class NotImplementedError extends Error

Throwing this exception can be a temporary replacement for a method body that remains to be implemented. For instance, the exception is thrown by Predef.???.

abstract final class Nothing extends Any

Nothing is - together with scala.Null - at the bottom of Scala's type hierarchy.

Nothing is a subtype of every other type (including scala.Null); there exist no instances of this type. Although type Nothing is uninhabited, it is nevertheless useful in several ways. For instance, the Scala library defines a value scala.collection.immutable.Nil of type List[Nothing]. Because lists are covariant in Scala, this makes scala.collection.immutable.Nil an instance of List[T], for any element of type T.

Another usage for Nothing is the return type for methods which never return normally. One example is method error in scala.sys, which always throws an exception.

abstract final class Null extends AnyRef

Null is - together with scala.Nothing - at the bottom of the Scala type hierarchy.

Null is a subtype of all reference types; its only instance is the null reference. Since Null is not a subtype of value types, null is not a member of any such type. For instance, it is not possible to assign null to a variable of type scala.Int.

type NullPointerException = java.lang.NullPointerException

type NumberFormatException = java.lang.NumberFormatException

type Numeric[T] = scala.math.Numeric[T]

sealed abstract class Option[+A] extends IterableOnce[A] with Product with Serializable

Represents optional values. Instances of Option are either an instance of scala.Some or the object None.

The most idiomatic way to use an scala.Option instance is to treat it as a collection or monad and use map,flatMap, filter, or foreach:

val name: Option[String] = request getParameter "name"
val upper = name map { _.trim } filter { _.length != 0 } map { _.toUpperCase }
println(upper getOrElse "")

Note that this is equivalent to

val upper = for {
  name <- request getParameter "name"
  trimmed <- Some(name.trim)
  upper <- Some(trimmed.toUpperCase) if trimmed.length != 0
} yield upper
println(upper getOrElse "")

Because of how for comprehension works, if None is returned from request.getParameter, the entire expression results in None

This allows for sophisticated chaining of scala.Option values without having to check for the existence of a value.

These are useful methods that exist for both scala.Some and None.

    isDefined — True if not empty isEmpty — True if empty nonEmpty — True if not empty orElse — Evaluate and return alternate optional value if empty getOrElse — Evaluate and return alternate value if empty get — Return value, throw exception if empty fold — Apply function on optional value, return default if empty map — Apply a function on the optional value flatMap — Same as map but function must return an optional value foreach — Apply a procedure on option value collect — Apply partial pattern match on optional value filter — An optional value satisfies predicate filterNot — An optional value doesn't satisfy predicate exists — Apply predicate on optional value, or false if empty forall — Apply predicate on optional value, or true if empty contains — Checks if value equals optional value, or false if empty zip — Combine two optional values to make a paired optional value unzip — Split an optional pair to two optional values unzip3 — Split an optional triple to three optional values toList — Unary list of optional value, otherwise the empty list

A less-idiomatic way to use scala.Option values is via pattern matching:

val nameMaybe = request getParameter "name"
nameMaybe match {
  case Some(name) =>
    println(name.trim.toUppercase)
  case None =>
    println("No name value")
}

Interacting with code that can occasionally return null can be safely wrapped in scala.Option to become None and scala.Some otherwise.

val abc = new java.util.HashMap[Int, String]
abc.put(1, "A")
bMaybe = Option(abc.get(2))
bMaybe match {
  case Some(b) =>
    println(s"Found $b")
  case None =>
    println("Not found")
}
Annotations
@SerialVersionUID()
Since

1.1

Note

Many of the methods in here are duplicative with those in the Traversable hierarchy, but they are duplicated for a reason: the implicit conversion tends to leave one with an Iterable in situations where one could have retained an Option.

type Ordered[T] = scala.math.Ordered[T]

type Ordering[T] = scala.math.Ordering[T]

trait PartialFunction[-A, +B] extends (A) => B

A partial function of type PartialFunction[A, B] is a unary function where the domain does not necessarily include all values of type A. The function isDefinedAt allows to test dynamically if a value is in the domain of the function.

Even if isDefinedAt returns true for an a: A, calling apply(a) may still throw an exception, so the following code is legal:

val f: PartialFunction[Int, Any] = { case _ => 1/0 }

It is the responsibility of the caller to call isDefinedAt before calling apply, because if isDefinedAt is false, it is not guaranteed apply will throw an exception to indicate an error condition. If an exception is not thrown, evaluation may result in an arbitrary value.

The main distinction between PartialFunction and scala.Function1 is that the user of a PartialFunction may choose to do something different with input that is declared to be outside its domain. For example:

val sample = 1 to 10
val isEven: PartialFunction[Int, String] = {
  case x if x % 2 == 0 => x+" is even"
}

// the method collect can use isDefinedAt to select which members to collect
val evenNumbers = sample collect isEven

val isOdd: PartialFunction[Int, String] = {
  case x if x % 2 == 1 => x+" is odd"
}

// the method orElse allows chaining another partial function to handle
// input outside the declared domain
val numbers = sample map (isEven orElse isOdd)
Since

1.0

Note

Optional Functions, PartialFunctions and extractor objects can be converted to each other as shown in the following table. | How to convert ... | to a PartialFunction | to an optional Function | to an extractor | | :---: | --- | --- | --- | | from a PartialFunction | Predef.identity | lift | Predef.identity | | from optional Function | Function.UnliftOps#unlift or Function.unlift | Predef.identity | Function.UnliftOps#unlift | | from an extractor | { case extractor(x) => x } | extractor.unapply _ | Predef.identity |

type PartialOrdering[T] = scala.math.PartialOrdering[T]

type PartiallyOrdered[T] = scala.math.PartiallyOrdered[T]

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.

Since

2.3

trait Product1[+T1] extends Product

Product1 is a Cartesian product of 1 component.

Since

2.3

trait Product10[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10] extends Product

Product10 is a Cartesian product of 10 components.

Since

2.3

trait Product11[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11] extends Product

Product11 is a Cartesian product of 11 components.

Since

2.3

trait Product12[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12] extends Product

Product12 is a Cartesian product of 12 components.

Since

2.3

trait Product13[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13] extends Product

Product13 is a Cartesian product of 13 components.

Since

2.3

trait Product14[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14] extends Product

Product14 is a Cartesian product of 14 components.

Since

2.3

trait Product15[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15] extends Product

Product15 is a Cartesian product of 15 components.

Since

2.3

trait Product16[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16] extends Product

Product16 is a Cartesian product of 16 components.

Since

2.3

trait Product17[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17] extends Product

Product17 is a Cartesian product of 17 components.

Since

2.3

trait Product18[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18] extends Product

Product18 is a Cartesian product of 18 components.

Since

2.3

trait Product19[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18, +T19] extends Product

Product19 is a Cartesian product of 19 components.

Since

2.3

trait Product2[+T1, +T2] extends Product

Product2 is a Cartesian product of 2 components.

Since

2.3

trait Product20[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18, +T19, +T20] extends Product

Product20 is a Cartesian product of 20 components.

Since

2.3

trait Product21[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18, +T19, +T20, +T21] extends Product

Product21 is a Cartesian product of 21 components.

Since

2.3

trait Product22[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18, +T19, +T20, +T21, +T22] extends Product

Product22 is a Cartesian product of 22 components.

Since

2.3

trait Product3[+T1, +T2, +T3] extends Product

Product3 is a Cartesian product of 3 components.

Since

2.3

trait Product4[+T1, +T2, +T3, +T4] extends Product

Product4 is a Cartesian product of 4 components.

Since

2.3

trait Product5[+T1, +T2, +T3, +T4, +T5] extends Product

Product5 is a Cartesian product of 5 components.

Since

2.3

trait Product6[+T1, +T2, +T3, +T4, +T5, +T6] extends Product

Product6 is a Cartesian product of 6 components.

Since

2.3

trait Product7[+T1, +T2, +T3, +T4, +T5, +T6, +T7] extends Product

Product7 is a Cartesian product of 7 components.

Since

2.3

trait Product8[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8] extends Product

Product8 is a Cartesian product of 8 components.

Since

2.3

trait Product9[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9] extends Product

Product9 is a Cartesian product of 9 components.

Since

2.3

type Range = scala.collection.immutable.Range

type Right[+A, +B] = scala.util.Right[A, B]

type RuntimeException = java.lang.RuntimeException

case class ScalaReflectionException(msg: String) extends Exception with Product with Serializable

type Seq[+A] = scala.collection.immutable.Seq[A]

Annotations
@migration
Migration

(Changed in version 2.13.0) scala.Seq is now scala.collection.immutable.Seq instead of scala.collection.Seq

class SerialVersionUID extends Annotation with ConstantAnnotation

Annotation for specifying the serialVersionUID field of a (serializable) class.

On the JVM, a class with this annotation will receive a private, static, and final field called serialVersionUID with the provided value, which the JVM's serialization mechanism uses to determine serialization compatibility between different versions of a class.

Annotations
@deprecatedInheritance("Scheduled for being final in 2.14", "2.13.0")
See also

java.io.Serializable

Serializable

type Serializable = java.io.Serializable

abstract final class Short extends AnyVal

Short, a 16-bit signed integer (equivalent to Java's short primitive type) is a subtype of scala.AnyVal. Instances of Short are not represented by an object in the underlying runtime system.

There is an implicit conversion from scala.Short => scala.runtime.RichShort which provides useful non-primitive operations.

final trait Singleton extends Any

Singleton is used by the compiler as a supertype for singleton types. This includes literal types, as they are also singleton types.

scala> object A { val x = 42 }
defined object A

scala> implicitly[A.type <:< Singleton]
res12: A.type <:< Singleton = generalized constraint

scala> implicitly[A.x.type <:< Singleton]
res13: A.x.type <:< Singleton = generalized constraint

scala> implicitly[42 <:< Singleton]
res14: 42 <:< Singleton = generalized constraint

scala> implicitly[Int <:< Singleton]
^
error: Cannot prove that Int <:< Singleton.

Singleton has a special meaning when it appears as an upper bound on a formal type parameter. Normally, type inference in Scala widens singleton types to the underlying non-singleton type. When a type parameter has an explicit upper bound of Singleton, the compiler infers a singleton type.

scala> def check42[T](x: T)(implicit ev: T =:= 42): T = x
check42: [T](x: T)(implicit ev: T =:= 42)T

scala> val x1 = check42(42)
^
error: Cannot prove that Int =:= 42.

scala> def singleCheck42[T <: Singleton](x: T)(implicit ev: T =:= 42): T = x
singleCheck42: [T <: Singleton](x: T)(implicit ev: T =:= 42)T

scala> val x2 = singleCheck42(42)
x2: Int = 42

See also SIP-23 about Literal-based Singleton Types.

final case class Some[+A](value: A) extends Option[A] with Product with Serializable

Class Some[A] represents existing values of type A.

Annotations
@SerialVersionUID()
Since

1.0

trait Specializable extends AnyRef

A common supertype for companions of specializable types. Should not be extended in user code.

type StringBuilder = scala.collection.mutable.StringBuilder

case class StringContext(parts: String*) extends Product with Serializable

This class provides the basic mechanism to do String Interpolation. String Interpolation allows users to embed variable references directly in *processed* string literals. Here's an example:

val name = "James"
println(s"Hello, $name")  // Hello, James

Any processed string literal is rewritten as an instantiation and method call against this class. For example:

s"Hello, $name"

is rewritten to be:

StringContext("Hello, ", "").s(name)

By default, this class provides the raw, s and f methods as available interpolators.

To provide your own string interpolator, create an implicit class which adds a method to StringContext. Here's an example:

implicit class JsonHelper(private val sc: StringContext) extends AnyVal {
  def json(args: Any*): JSONObject = ...
}
val x: JSONObject = json"{ a: $a }"

Here the JsonHelper extension class implicitly adds the json method to StringContext which can be used for json string literals.

parts

The parts that make up the interpolated string, without the expressions that get inserted by interpolation.

Since

2.10.0

type StringIndexOutOfBoundsException = java.lang.StringIndexOutOfBoundsException

final class Symbol extends Serializable

This class provides a simple way to get unique objects for equal strings. Since symbols are interned, they can be compared using reference equality. Instances of Symbol can be created easily with Scala's built-in quote mechanism.

For instance, the Scala term 'mysym will invoke the constructor of the Symbol class in the following way: Symbol("mysym").

Since

1.7

type Throwable = java.lang.Throwable

final case class Tuple1[+T1](_1: T1) extends Product1[T1] with Product with Serializable

A tuple of 1 elements; the canonical representation of a scala.Product1.

_1

Element 1 of this Tuple1

final case class Tuple10[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10) extends Product10[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10] with Product with Serializable

A tuple of 10 elements; the canonical representation of a scala.Product10.

_1

Element 1 of this Tuple10

_2

Element 2 of this Tuple10

_3

Element 3 of this Tuple10

_4

Element 4 of this Tuple10

_5

Element 5 of this Tuple10

_6

Element 6 of this Tuple10

_7

Element 7 of this Tuple10

_8

Element 8 of this Tuple10

_9

Element 9 of this Tuple10

_10

Element 10 of this Tuple10

final case class Tuple11[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11) extends Product11[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11] with Product with Serializable

A tuple of 11 elements; the canonical representation of a scala.Product11.

_1

Element 1 of this Tuple11

_2

Element 2 of this Tuple11

_3

Element 3 of this Tuple11

_4

Element 4 of this Tuple11

_5

Element 5 of this Tuple11

_6

Element 6 of this Tuple11

_7

Element 7 of this Tuple11

_8

Element 8 of this Tuple11

_9

Element 9 of this Tuple11

_10

Element 10 of this Tuple11

_11

Element 11 of this Tuple11

final case class Tuple12[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12) extends Product12[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12] with Product with Serializable

A tuple of 12 elements; the canonical representation of a scala.Product12.

_1

Element 1 of this Tuple12

_2

Element 2 of this Tuple12

_3

Element 3 of this Tuple12

_4

Element 4 of this Tuple12

_5

Element 5 of this Tuple12

_6

Element 6 of this Tuple12

_7

Element 7 of this Tuple12

_8

Element 8 of this Tuple12

_9

Element 9 of this Tuple12

_10

Element 10 of this Tuple12

_11

Element 11 of this Tuple12

_12

Element 12 of this Tuple12

final case class Tuple13[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13) extends Product13[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13] with Product with Serializable

A tuple of 13 elements; the canonical representation of a scala.Product13.

_1

Element 1 of this Tuple13

_2

Element 2 of this Tuple13

_3

Element 3 of this Tuple13

_4

Element 4 of this Tuple13

_5

Element 5 of this Tuple13

_6

Element 6 of this Tuple13

_7

Element 7 of this Tuple13

_8

Element 8 of this Tuple13

_9

Element 9 of this Tuple13

_10

Element 10 of this Tuple13

_11

Element 11 of this Tuple13

_12

Element 12 of this Tuple13

_13

Element 13 of this Tuple13

final case class Tuple14[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14) extends Product14[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14] with Product with Serializable

A tuple of 14 elements; the canonical representation of a scala.Product14.

_1

Element 1 of this Tuple14

_2

Element 2 of this Tuple14

_3

Element 3 of this Tuple14

_4

Element 4 of this Tuple14

_5

Element 5 of this Tuple14

_6

Element 6 of this Tuple14

_7

Element 7 of this Tuple14

_8

Element 8 of this Tuple14

_9

Element 9 of this Tuple14

_10

Element 10 of this Tuple14

_11

Element 11 of this Tuple14

_12

Element 12 of this Tuple14

_13

Element 13 of this Tuple14

_14

Element 14 of this Tuple14

final case class Tuple15[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14, _15: T15) extends Product15[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15] with Product with Serializable

A tuple of 15 elements; the canonical representation of a scala.Product15.

_1

Element 1 of this Tuple15

_2

Element 2 of this Tuple15

_3

Element 3 of this Tuple15

_4

Element 4 of this Tuple15

_5

Element 5 of this Tuple15

_6

Element 6 of this Tuple15

_7

Element 7 of this Tuple15

_8

Element 8 of this Tuple15

_9

Element 9 of this Tuple15

_10

Element 10 of this Tuple15

_11

Element 11 of this Tuple15

_12

Element 12 of this Tuple15

_13

Element 13 of this Tuple15

_14

Element 14 of this Tuple15

_15

Element 15 of this Tuple15

final case class Tuple16[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14, _15: T15, _16: T16) extends Product16[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16] with Product with Serializable

A tuple of 16 elements; the canonical representation of a scala.Product16.

_1

Element 1 of this Tuple16

_2

Element 2 of this Tuple16

_3

Element 3 of this Tuple16

_4

Element 4 of this Tuple16

_5

Element 5 of this Tuple16

_6

Element 6 of this Tuple16

_7

Element 7 of this Tuple16

_8

Element 8 of this Tuple16

_9

Element 9 of this Tuple16

_10

Element 10 of this Tuple16

_11

Element 11 of this Tuple16

_12

Element 12 of this Tuple16

_13

Element 13 of this Tuple16

_14

Element 14 of this Tuple16

_15

Element 15 of this Tuple16

_16

Element 16 of this Tuple16

final case class Tuple17[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14, _15: T15, _16: T16, _17: T17) extends Product17[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17] with Product with Serializable

A tuple of 17 elements; the canonical representation of a scala.Product17.

_1

Element 1 of this Tuple17

_2

Element 2 of this Tuple17

_3

Element 3 of this Tuple17

_4

Element 4 of this Tuple17

_5

Element 5 of this Tuple17

_6

Element 6 of this Tuple17

_7

Element 7 of this Tuple17

_8

Element 8 of this Tuple17

_9

Element 9 of this Tuple17

_10

Element 10 of this Tuple17

_11

Element 11 of this Tuple17

_12

Element 12 of this Tuple17

_13

Element 13 of this Tuple17

_14

Element 14 of this Tuple17

_15

Element 15 of this Tuple17

_16

Element 16 of this Tuple17

_17

Element 17 of this Tuple17

final case class Tuple18[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14, _15: T15, _16: T16, _17: T17, _18: T18) extends Product18[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18] with Product with Serializable

A tuple of 18 elements; the canonical representation of a scala.Product18.

_1

Element 1 of this Tuple18

_2

Element 2 of this Tuple18

_3

Element 3 of this Tuple18

_4

Element 4 of this Tuple18

_5

Element 5 of this Tuple18

_6

Element 6 of this Tuple18

_7

Element 7 of this Tuple18

_8

Element 8 of this Tuple18

_9

Element 9 of this Tuple18

_10

Element 10 of this Tuple18

_11

Element 11 of this Tuple18

_12

Element 12 of this Tuple18

_13

Element 13 of this Tuple18

_14

Element 14 of this Tuple18

_15

Element 15 of this Tuple18

_16

Element 16 of this Tuple18

_17

Element 17 of this Tuple18

_18

Element 18 of this Tuple18

final case class Tuple19[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18, +T19](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14, _15: T15, _16: T16, _17: T17, _18: T18, _19: T19) extends Product19[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19] with Product with Serializable

A tuple of 19 elements; the canonical representation of a scala.Product19.

_1

Element 1 of this Tuple19

_2

Element 2 of this Tuple19

_3

Element 3 of this Tuple19

_4

Element 4 of this Tuple19

_5

Element 5 of this Tuple19

_6

Element 6 of this Tuple19

_7

Element 7 of this Tuple19

_8

Element 8 of this Tuple19

_9

Element 9 of this Tuple19

_10

Element 10 of this Tuple19

_11

Element 11 of this Tuple19

_12

Element 12 of this Tuple19

_13

Element 13 of this Tuple19

_14

Element 14 of this Tuple19

_15

Element 15 of this Tuple19

_16

Element 16 of this Tuple19

_17

Element 17 of this Tuple19

_18

Element 18 of this Tuple19

_19

Element 19 of this Tuple19

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

final case class Tuple20[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18, +T19, +T20](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14, _15: T15, _16: T16, _17: T17, _18: T18, _19: T19, _20: T20) extends Product20[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20] with Product with Serializable

A tuple of 20 elements; the canonical representation of a scala.Product20.

_1

Element 1 of this Tuple20

_2

Element 2 of this Tuple20

_3

Element 3 of this Tuple20

_4

Element 4 of this Tuple20

_5

Element 5 of this Tuple20

_6

Element 6 of this Tuple20

_7

Element 7 of this Tuple20

_8

Element 8 of this Tuple20

_9

Element 9 of this Tuple20

_10

Element 10 of this Tuple20

_11

Element 11 of this Tuple20

_12

Element 12 of this Tuple20

_13

Element 13 of this Tuple20

_14

Element 14 of this Tuple20

_15

Element 15 of this Tuple20

_16

Element 16 of this Tuple20

_17

Element 17 of this Tuple20

_18

Element 18 of this Tuple20

_19

Element 19 of this Tuple20

_20

Element 20 of this Tuple20

final case class Tuple21[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18, +T19, +T20, +T21](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14, _15: T15, _16: T16, _17: T17, _18: T18, _19: T19, _20: T20, _21: T21) extends Product21[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21] with Product with Serializable

A tuple of 21 elements; the canonical representation of a scala.Product21.

_1

Element 1 of this Tuple21

_2

Element 2 of this Tuple21

_3

Element 3 of this Tuple21

_4

Element 4 of this Tuple21

_5

Element 5 of this Tuple21

_6

Element 6 of this Tuple21

_7

Element 7 of this Tuple21

_8

Element 8 of this Tuple21

_9

Element 9 of this Tuple21

_10

Element 10 of this Tuple21

_11

Element 11 of this Tuple21

_12

Element 12 of this Tuple21

_13

Element 13 of this Tuple21

_14

Element 14 of this Tuple21

_15

Element 15 of this Tuple21

_16

Element 16 of this Tuple21

_17

Element 17 of this Tuple21

_18

Element 18 of this Tuple21

_19

Element 19 of this Tuple21

_20

Element 20 of this Tuple21

_21

Element 21 of this Tuple21

final case class Tuple22[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9, +T10, +T11, +T12, +T13, +T14, +T15, +T16, +T17, +T18, +T19, +T20, +T21, +T22](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9, _10: T10, _11: T11, _12: T12, _13: T13, _14: T14, _15: T15, _16: T16, _17: T17, _18: T18, _19: T19, _20: T20, _21: T21, _22: T22) extends Product22[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22] with Product with Serializable

A tuple of 22 elements; the canonical representation of a scala.Product22.

_1

Element 1 of this Tuple22

_2

Element 2 of this Tuple22

_3

Element 3 of this Tuple22

_4

Element 4 of this Tuple22

_5

Element 5 of this Tuple22

_6

Element 6 of this Tuple22

_7

Element 7 of this Tuple22

_8

Element 8 of this Tuple22

_9

Element 9 of this Tuple22

_10

Element 10 of this Tuple22

_11

Element 11 of this Tuple22

_12

Element 12 of this Tuple22

_13

Element 13 of this Tuple22

_14

Element 14 of this Tuple22

_15

Element 15 of this Tuple22

_16

Element 16 of this Tuple22

_17

Element 17 of this Tuple22

_18

Element 18 of this Tuple22

_19

Element 19 of this Tuple22

_20

Element 20 of this Tuple22

_21

Element 21 of this Tuple22

_22

Element 22 of this Tuple22

final case class Tuple3[+T1, +T2, +T3](_1: T1, _2: T2, _3: T3) extends Product3[T1, T2, T3] with Product with Serializable

A tuple of 3 elements; the canonical representation of a scala.Product3.

_1

Element 1 of this Tuple3

_2

Element 2 of this Tuple3

_3

Element 3 of this Tuple3

final case class Tuple4[+T1, +T2, +T3, +T4](_1: T1, _2: T2, _3: T3, _4: T4) extends Product4[T1, T2, T3, T4] with Product with Serializable

A tuple of 4 elements; the canonical representation of a scala.Product4.

_1

Element 1 of this Tuple4

_2

Element 2 of this Tuple4

_3

Element 3 of this Tuple4

_4

Element 4 of this Tuple4

final case class Tuple5[+T1, +T2, +T3, +T4, +T5](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5) extends Product5[T1, T2, T3, T4, T5] with Product with Serializable

A tuple of 5 elements; the canonical representation of a scala.Product5.

_1

Element 1 of this Tuple5

_2

Element 2 of this Tuple5

_3

Element 3 of this Tuple5

_4

Element 4 of this Tuple5

_5

Element 5 of this Tuple5

final case class Tuple6[+T1, +T2, +T3, +T4, +T5, +T6](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6) extends Product6[T1, T2, T3, T4, T5, T6] with Product with Serializable

A tuple of 6 elements; the canonical representation of a scala.Product6.

_1

Element 1 of this Tuple6

_2

Element 2 of this Tuple6

_3

Element 3 of this Tuple6

_4

Element 4 of this Tuple6

_5

Element 5 of this Tuple6

_6

Element 6 of this Tuple6

final case class Tuple7[+T1, +T2, +T3, +T4, +T5, +T6, +T7](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7) extends Product7[T1, T2, T3, T4, T5, T6, T7] with Product with Serializable

A tuple of 7 elements; the canonical representation of a scala.Product7.

_1

Element 1 of this Tuple7

_2

Element 2 of this Tuple7

_3

Element 3 of this Tuple7

_4

Element 4 of this Tuple7

_5

Element 5 of this Tuple7

_6

Element 6 of this Tuple7

_7

Element 7 of this Tuple7

final case class Tuple8[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8) extends Product8[T1, T2, T3, T4, T5, T6, T7, T8] with Product with Serializable

A tuple of 8 elements; the canonical representation of a scala.Product8.

_1

Element 1 of this Tuple8

_2

Element 2 of this Tuple8

_3

Element 3 of this Tuple8

_4

Element 4 of this Tuple8

_5

Element 5 of this Tuple8

_6

Element 6 of this Tuple8

_7

Element 7 of this Tuple8

_8

Element 8 of this Tuple8

final case class Tuple9[+T1, +T2, +T3, +T4, +T5, +T6, +T7, +T8, +T9](_1: T1, _2: T2, _3: T3, _4: T4, _5: T5, _6: T6, _7: T7, _8: T8, _9: T9) extends Product9[T1, T2, T3, T4, T5, T6, T7, T8, T9] with Product with Serializable

A tuple of 9 elements; the canonical representation of a scala.Product9.

_1

Element 1 of this Tuple9

_2

Element 2 of this Tuple9

_3

Element 3 of this Tuple9

_4

Element 4 of this Tuple9

_5

Element 5 of this Tuple9

_6

Element 6 of this Tuple9

_7

Element 7 of this Tuple9

_8

Element 8 of this Tuple9

_9

Element 9 of this Tuple9

final case class UninitializedFieldError(msg: String) extends RuntimeException with Product with Serializable

This class implements errors which are thrown whenever a field is used before it has been initialized.

Such runtime checks are not emitted by default. They can be enabled by the -Xcheckinit compiler option.

Since

2.7

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.

type UnsupportedOperationException = java.lang.UnsupportedOperationException

final class ValueOf[T] extends AnyVal

ValueOf[T] provides the unique value of the type T where T is a type which has a single inhabitant. Eligible types are singleton types of the form stablePath.type, Unit and singleton types corresponding to value literals.

Instances of ValueOf[T] are provided implicitly for all eligible types. Typically an instance would be required where a runtime value corresponding to a type level computation is needed.

For example, we might define a type Residue[M <: Int] corresponding to the group of integers modulo M. We could then mandate that residues can be summed only when they are parameterized by the same modulus,

case class Residue[M <: Int](n: Int) extends AnyVal {
  def +(rhs: Residue[M])(implicit m: ValueOf[M]): Residue[M] =
    Residue((this.n + rhs.n) % valueOf[M])
}

val fiveModTen = Residue[10](5)
val nineModTen = Residue[10](9)

fiveModTen + nineModTen    // OK == Residue[10](4)

val fourModEleven = Residue[11](4)

fiveModTen + fourModEleven // compiler error: type mismatch;
                           //   found   : Residue[11]
                           //   required: Residue[10]

Notice that here the modulus is encoded in the type of the values and so does not incur any additional per-value storage cost. When a runtime value of the modulus is required in the implementation of + it is provided at the call site via the implicit argument m of type ValueOf[M].

Annotations
@implicitNotFound("No singleton value available for ${T}.")

type Vector[+A] = scala.collection.immutable.Vector[A]

class deprecated extends Annotation with StaticAnnotation

An annotation that designates that a definition is deprecated. A deprecation warning is issued upon usage of the annotated definition.

Library authors should state the library's deprecation policy in their documentation to give developers guidance on how long a deprecated definition will be preserved.

Library authors should prepend the name of their library to the version number to help developers distinguish deprecations coming from different libraries:

@deprecated("this method will be removed", "FooLib 12.0")
def oldMethod(x: Int) = ...

The compiler will emit deprecation warnings grouped by library and version:

oldMethod(1)
oldMethod(2)
aDeprecatedMethodFromLibraryBar(3, 4)

// warning: there was one deprecation warning (since BarLib 3.2)
// warning: there were two deprecation warnings (since FooLib 12.0)
// warning: there were three deprecation warnings in total; re-run with -deprecation for details

@deprecated in the Scala language and its standard library

A deprecated element of the Scala language or a definition in the Scala standard library will be preserved at least for the current major version.

This means that an element deprecated in some 2.13.x release will be preserved in all 2.13.x releases, but may be removed in 2.14. (A deprecated element might be kept longer to ease migration, but developers should not rely on this.)

Annotations
@getter() @setter() @beanGetter() @beanSetter() @deprecatedInheritance("Scheduled for being final in 2.14", "2.13.0")
Since

2.3

See also

The official documentation on binary compatibility.

scala.deprecatedInheritance

scala.deprecatedOverriding

scala.deprecatedName

final class deprecatedInheritance extends Annotation with StaticAnnotation

An annotation that designates that inheriting from a class is deprecated.

This is usually done to warn about a non-final class being made final in a future version. Sub-classing such a class then generates a warning.

No warnings are generated if the subclass is in the same compilation unit.

Library authors should state the library's deprecation policy in their documentation to give developers guidance on when a type annotated with @deprecatedInheritance will be finalized.

Library authors should prepend the name of their library to the version number to help developers distinguish deprecations coming from different libraries:

@deprecatedInheritance("this class will be made final", "FooLib 12.0")
class Foo
val foo = new Foo     // no deprecation warning
class Bar extends Foo
// warning: inheritance from class Foo is deprecated (since FooLib 12.0): this class will be made final
// class Bar extends Foo
//                   ^
Annotations
@getter() @setter() @beanGetter() @beanSetter()
Since

2.10

See also

scala.deprecated

scala.deprecatedOverriding

scala.deprecatedName

class deprecatedName extends Annotation with StaticAnnotation

An annotation that designates that the name of a parameter is deprecated.

Using this name in a named argument generates a deprecation warning.

Library authors should state the library's deprecation policy in their documentation to give developers guidance on how long a deprecated name will be preserved.

Library authors should prepend the name of their library to the version number to help developers distinguish deprecations coming from different libraries:

def inc(x: Int, @deprecatedName("y", "FooLib 12.0") n: Int): Int = x + n
inc(1, y = 2)

will produce the following warning:

warning: the parameter name y is deprecated (since FooLib 12.0): use n instead
inc(1, y = 2)
         ^
Annotations
@param() @deprecatedInheritance("Scheduled for being final in 2.14", "2.13.0")
Since

2.8.1

See also

scala.deprecated

scala.deprecatedInheritance

scala.deprecatedOverriding

class deprecatedOverriding extends Annotation with StaticAnnotation

An annotation that designates that overriding a member is deprecated.

Overriding such a member in a sub-class then generates a warning.

Library authors should state the library's deprecation policy in their documentation to give developers guidance on when a method annotated with @deprecatedOverriding will be finalized.

Library authors should prepend the name of their library to the version number to help developers distinguish deprecations coming from different libraries:

class Foo {
  @deprecatedOverriding("this method will be made final", "FooLib 12.0")
  def add(x: Int, y: Int) = x + y
}
class Bar extends Foo // no deprecation warning
class Baz extends Foo {
  override def add(x: Int, y: Int) = x - y
}
// warning: overriding method add in class Foo is deprecated (since FooLib 12.0): this method will be made final
// override def add(x: Int, y: Int) = x - y
//              ^
Annotations
@getter() @setter() @beanGetter() @beanSetter() @deprecatedInheritance("Scheduled for being final in 2.14", "2.13.0")
Since

2.10

See also

scala.deprecated

scala.deprecatedInheritance

scala.deprecatedName

class inline extends Annotation with StaticAnnotation

An annotation for methods that the optimizer should inline.

Note that by default, the Scala optimizer is disabled and no callsites are inlined. See -opt:help for information on how to enable the optimizer and inliner.

When inlining is enabled, the inliner will always try to inline methods or callsites annotated @inline (under the condition that inlining from the defining class is allowed, see -opt-inline-from:help). If inlining is not possible, for example because the method is not final, an optimizer warning will be issued. See -opt-warnings:help for details.

Examples:

@inline   final def f1(x: Int) = x
@noinline final def f2(x: Int) = x
          final def f3(x: Int) = x

 def t1 = f1(1)              // inlined if possible
 def t2 = f2(1)              // not inlined
 def t3 = f3(1)              // may be inlined (the inliner heuristics can select the callsite)
 def t4 = f1(1): @noinline   // not inlined (override at callsite)
 def t5 = f2(1): @inline     // inlined if possible (override at callsite)
 def t6 = f3(1): @inline     // inlined if possible
 def t7 = f3(1): @noinline   // not inlined
}

Note: parentheses are required when annotating a callsite within a larger expression.

def t1 = f1(1) + f1(1): @noinline   // equivalent to (f1(1) + f1(1)): @noinline
def t2 = f1(1) + (f1(1): @noinline) // the second call to f1 is not inlined
Annotations
@deprecatedInheritance("Scheduled for being final in 2.14", "2.13.0")

class native extends Annotation with StaticAnnotation

Marker for native methods.

@native def f(x: Int, y: List[Long]): String = ...

A @native method is compiled to the platform's native method, while discarding the method's body (if any). The body will be type checked if present.

A method marked @native must be a member of a class, not a trait (since 2.12).

Annotations
@deprecatedInheritance("Scheduled for being final in 2.14", "2.13.0")
Since

2.6

final class noinline extends Annotation with StaticAnnotation

An annotation for methods that the optimizer should not inline.

Note that by default, the Scala optimizer is disabled and no callsites are inlined. See -opt:help for information how to enable the optimizer and inliner.

When inlining is enabled, the inliner will never inline methods or callsites annotated @noinline.

Examples:

@inline   final def f1(x: Int) = x
@noinline final def f2(x: Int) = x
          final def f3(x: Int) = x

 def t1 = f1(1)              // inlined if possible
 def t2 = f2(1)              // not inlined
 def t3 = f3(1)              // may be inlined (the inliner heuristics can select the callsite)
 def t4 = f1(1): @noinline   // not inlined (override at callsite)
 def t5 = f2(1): @inline     // inlined if possible (override at callsite)
 def t6 = f3(1): @inline     // inlined if possible
 def t7 = f3(1): @noinline   // not inlined
}

Note: parentheses are required when annotating a callsite within a larger expression.

def t1 = f1(1) + f1(1): @noinline   // equivalent to (f1(1) + f1(1)): @noinline
def t2 = f1(1) + (f1(1): @noinline) // the second call to f1 is not inlined

final class specialized extends Annotation with StaticAnnotation

Annotate type parameters on which code should be automatically specialized. For example:

class MyList[@specialized T] ...

Type T can be specialized on a subset of the primitive types by specifying a list of primitive types to specialize at:

class MyList[@specialized(Int, Double, Boolean) T] ..
Since

2.8

final class throws[T <: Throwable] extends Annotation with StaticAnnotation

Annotation for specifying the exceptions thrown by a method. For example:

class Reader(fname: String) {
  private val in = new BufferedReader(new FileReader(fname))
  @throws[IOException]("if the file doesn't exist")
  def read() = in.read()
}
Since

2.1

final class transient extends Annotation with StaticAnnotation

Annotations
@field()

final class unchecked extends Annotation

An annotation to designate that the annotated entity should not be considered for additional compiler checks. Specific applications include annotating the subject of a match expression to suppress exhaustiveness warnings, and annotating a type argument in a match case to suppress unchecked warnings.

Such suppression should be used with caution, without which one may encounter scala.MatchError or java.lang.ClassCastException at runtime. In most cases one can and should address the warning instead of suppressing it.

object Test extends App {
  // This would normally warn "match is not exhaustive"
  // because `None` is not covered.
  def f(x: Option[String]) = (x: @unchecked) match { case Some(y) => y }
  // This would normally warn "type pattern is unchecked"
  // but here will blindly cast the head element to String.
  def g(xs: Any) = xs match { case x: List[String @unchecked] => x.head }
}
Since

2.4

final class volatile extends Annotation with StaticAnnotation

Annotations
@field()

Value Members

val +:: scala.collection.+:.type

val :+: scala.collection.:+.type

val ::: scala.collection.immutable.::.type

val AnyRef: Specializable

val BigDecimal: scala.math.BigDecimal.type

val BigInt: scala.math.BigInt.type

val Either: scala.util.Either.type

val Equiv: scala.math.Equiv.type

val Fractional: scala.math.Fractional.type

val IndexedSeq: scala.collection.immutable.IndexedSeq.type

val Integral: scala.math.Integral.type

val Iterable: scala.collection.Iterable.type

val Iterator: scala.collection.Iterator.type

val LazyList: scala.collection.immutable.LazyList.type

val Left: scala.util.Left.type

val List: scala.collection.immutable.List.type

val Nil: scala.collection.immutable.Nil.type

val Numeric: scala.math.Numeric.type

val Ordered: scala.math.Ordered.type

val Ordering: scala.math.Ordering.type

val Range: scala.collection.immutable.Range.type

val Seq: scala.collection.immutable.Seq.type

val StringBuilder: scala.collection.mutable.StringBuilder.type

val Vector: scala.collection.immutable.Vector.type

object #::

object <:< extends java.io.Serializable

object Array extends java.io.Serializable

Utility methods for operating on arrays. For example:

val a = Array(1, 2)
val b = Array.ofDim[Int](2)
val c = Array.concat(a, b)

where the array objects a, b and c have respectively the values Array(1, 2), Array(0, 0) and Array(1, 2, 0, 0).

Since

1.0

object Boolean extends AnyValCompanion

object Byte extends AnyValCompanion

object Char extends AnyValCompanion

object Console extends AnsiColor

Implements functionality for printing Scala values on the terminal. For reading values use StdIn. Also defines constants for marking up text on ANSI terminals.

Console Output

Use the print methods to output text.

scala> Console.printf(
  "Today the outside temperature is a balmy %.1f°C. %<.1f°C beats the previous record of %.1f°C.\n",
  -137.0,
  -135.05)
Today the outside temperature is a balmy -137.0°C. -137.0°C beats the previous record of -135.1°C.

ANSI escape codes

Use the ANSI escape codes for colorizing console output either to STDOUT or STDERR.

import Console.{GREEN, RED, RESET, YELLOW_B, UNDERLINED}

object PrimeTest {

  def isPrime(): Unit = {

    val candidate = io.StdIn.readInt().ensuring(_ > 1)

    val prime = (2 to candidate - 1).forall(candidate % _ != 0)

    if (prime)
      Console.println(s"${RESET}${GREEN}yes${RESET}")
    else
      Console.err.println(s"${RESET}${YELLOW_B}${RED}${UNDERLINED}NO!${RESET}")
  }

  def main(args: Array[String]): Unit = isPrime()

}
$ scala PrimeTest
1234567891
yes
$ scala PrimeTest
56474
NO!

IO redefinition

Use IO redefinition to temporarily swap in a different set of input and/or output streams. In this example the stream based method above is wrapped into a function.

import java.io.{ByteArrayOutputStream, StringReader}

object FunctionalPrimeTest {

  def isPrime(candidate: Int): Boolean = {

    val input = new StringReader(s"$candidate\n")
    val outCapture = new ByteArrayOutputStream
    val errCapture = new ByteArrayOutputStream

    Console.withIn(input) {
      Console.withOut(outCapture) {
        Console.withErr(errCapture) {
          PrimeTest.isPrime()
        }
      }
    }

    if (outCapture.toByteArray.nonEmpty) // "yes"
      true
    else if (errCapture.toByteArray.nonEmpty) // "NO!"
      false
    else throw new IllegalArgumentException(candidate.toString)
  }

  def main(args: Array[String]): Unit = {
    val primes = (2 to 50) filter (isPrime)
    println(s"First primes: $primes")
  }

}
$ scala FunctionalPrimeTest
First primes: Vector(2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47)
Since

1.0

object Double extends AnyValCompanion

object DummyImplicit

object Float extends AnyValCompanion

object Function

A module defining utility methods for higher-order functional programming.

Since

1.0

object Function1

object Int extends AnyValCompanion

object Long extends AnyValCompanion

object None extends Option[Nothing] with Product with Serializable

This case object represents non-existent values.

Annotations
@SerialVersionUID()
Since

1.0

object Option extends java.io.Serializable

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 }
Since

2.8

object Predef extends LowPriorityImplicits

The Predef object provides definitions that are accessible in all Scala compilation units without explicit qualification.

Commonly Used Types

Predef provides type aliases for types which are commonly used, such as the immutable collection types scala.collection.immutable.Map, scala.collection.immutable.Set, and the scala.collection.immutable.List constructors (scala.collection.immutable.:: and scala.collection.immutable.Nil).

Console Output

For basic console output, Predef provides convenience methods print and println, which are aliases of the methods in the object scala.Console.

Assertions

A set of assert functions are provided for use as a way to document and dynamically check invariants in code. Invocations of assert can be elided at compile time by providing the command line option -Xdisable-assertions, which raises -Xelide-below above elidable.ASSERTION, to the scalac command.

Variants of assert intended for use with static analysis tools are also provided: assume, require and ensuring. require and ensuring are intended for use as a means of design-by-contract style specification of pre- and post-conditions on functions, with the intention that these specifications could be consumed by a static analysis tool. For instance,

def addNaturals(nats: List[Int]): Int = {
  require(nats forall (_ >= 0), "List contains negative numbers")
  nats.foldLeft(0)(_ + _)
} ensuring(_ >= 0)

The declaration of addNaturals states that the list of integers passed should only contain natural numbers (i.e. non-negative), and that the result returned will also be natural. require is distinct from assert in that if the condition fails, then the caller of the function is to blame rather than a logical error having been made within addNaturals itself. ensuring is a form of assert that declares the guarantee the function is providing with regards to its return value.

Implicit Conversions

A number of commonly applied implicit conversions are also defined here, and in the parent type scala.LowPriorityImplicits. Implicit conversions are provided for the "widening" of numeric values, for instance, converting a Short value to a Long value as required, and to add additional higher-order functions to Array values. These are described in more detail in the documentation of scala.Array.

object Product1

object Product10

object Product11

object Product12

object Product13

object Product14

object Product15

object Product16

object Product17

object Product18

object Product19

object Product2

object Product20

object Product21

object Product22

object Product3

object Product4

object Product5

object Product6

object Product7

object Product8

object Product9

object Short extends AnyValCompanion

object Specializable

object StringContext extends java.io.Serializable

object Symbol extends UniquenessCache[String, Symbol] with java.io.Serializable

object Unit extends AnyValCompanion

Annotations
@compileTimeOnly("`Unit` companion object is not allowed in source; instead, use `()` for the unit value")

object language

The scala.language object controls the language features available to the programmer, as proposed in the SIP-18 document.

Each of these features has to be explicitly imported into the current scope to become available:

import language.postfixOps // or language._
List(1, 2, 3) reverse

The language features are:

object languageFeature

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/index.html