scala

package scala

Type members

Classlikes

object #::
sealed abstract class *:[+H, +T <: Tuple] extends NonEmptyTuple
Companion
object
object *:
Companion
class
@implicitNotFound(msg = "Cannot prove that ${From} <:< ${To}.")
sealed abstract class <:<[-From, +To] extends From => To with Serializable

An instance of A <:< B witnesses that A is a subtype of B.

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.

Type Params
From

a type which is proved a subtype of To

To

a type which is proved a supertype of From

See also

=:= for expressing equality constraints

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.
}
Companion
object
object <:<
Companion
class
@implicitNotFound(msg = "Cannot prove that ${From} =:= ${To}.")
sealed abstract class =:=[From, To] extends From <:< To with Serializable

An instance of A =:= B witnesses that the types A and B are equal.

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.

Type Params
From

a type which is proved equal to To

To

a type which is proved equal to From

See also

&lt;:&lt; for expressing subtyping constraints

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.
}
@nowarn("cat=deprecation&origin=scala\\.DelayedInit")
trait App extends DelayedInit

The App trait can be used to quickly turn objects into executable programs.

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.

object Array

Utility methods for operating on arrays.

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).

Companion
class
final class Array[T](_length: Int) extends Serializable with Cloneable

Arrays are mutable, indexed collections of values.

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.

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.

Companion
object
final abstract class Boolean extends AnyVal

Boolean (equivalent to Java's boolean primitive type) is a subtype of scala.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.

Companion
object
object Boolean extends AnyValCompanion
Companion
class
final abstract class Byte extends AnyVal

Byte, a 8-bit signed integer (equivalent to Java's byte primitive type) is a subtype of scala.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.

Companion
object
object Byte extends AnyValCompanion
Companion
class
@implicitNotFound("Values of types ${L} and ${R} cannot be compared with == or !=")
sealed trait CanEqual[-L, -R]

A marker trait indicating that values of type L can be compared to values of type R.

A marker trait indicating that values of type L can be compared to values of type R.

Companion
object
object CanEqual

Companion object containing a few universally known CanEqual instances.

Companion object containing a few universally known CanEqual instances. CanEqual instances involving primitive types or the Null type are handled directly in the compiler (see Implicits.synthesizedCanEqual), so they are not included here.

Companion
class
final abstract class Char extends AnyVal

Char, a 16-bit unsigned integer (equivalent to Java's char primitive type) is a subtype of scala.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.

Companion
object
object Char extends AnyValCompanion
Companion
class
object Console extends AnsiColor

Implements functionality for printing Scala values on the terminal.

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)

abstract class Conversion[-T, +U] extends T => U

A class for implicit values that can serve as implicit conversions The implicit resolution algorithm will act as if there existed the additional implicit definition:

A class for implicit values that can serve as implicit conversions The implicit resolution algorithm will act as if there existed the additional implicit definition:

def $implicitConversion[T, U](x: T)(c: Conversion[T, U]): U = c(x)

However, the presence of this definition would slow down implicit search since its outermost type matches any pair of types. Therefore, implicit search contains a special case in Implicits#discardForView which emulates the conversion in a more efficient way.

Note that this is a SAM class - function literals are automatically converted to the Conversion values.

Also note that in bootstrapped dotty, Predef.<:< should inherit from Conversion. This would cut the number of special cases in discardForView from two to one.

The Conversion class can also be used to convert explicitly, using the convert extension method.

final abstract 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.

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.

Companion
object
object Double extends AnyValCompanion
Companion
class
final class DummyImplicit

A type for which there is always an implicit value.

A type for which there is always an implicit value.

Companion
object
Companion
class
trait Dynamic

A marker trait that enables dynamic invocations.

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.

object EmptyTuple extends Tuple

A tuple of 0 elements.

A tuple of 0 elements.

@SerialVersionUID(8476000850333817230L)
abstract class Enumeration(initial: Int) extends Serializable

Defines a finite set of values specific to the enumeration.

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.

Value Params
initial

The initial value from which to count the integers that identifies values at run-time.

Example

// 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 PlanetVal(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): PlanetVal = x.asInstanceOf[PlanetVal]
 val G: Double = 6.67300E-11
 val Mercury = PlanetVal(3.303e+23, 2.4397e6)
 val Venus   = PlanetVal(4.869e+24, 6.0518e6)
 val Earth   = PlanetVal(5.976e+24, 6.37814e6)
 val Mars    = PlanetVal(6.421e+23, 3.3972e6)
 val Jupiter = PlanetVal(1.9e+27, 7.1492e7)
 val Saturn  = PlanetVal(5.688e+26, 6.0268e7)
 val Uranus  = PlanetVal(8.686e+25, 2.5559e7)
 val Neptune = PlanetVal(1.024e+26, 2.4746e7)
}
println(Planet.values.filter(_.radius > 7.0e6))
// output:
// Planet.ValueSet(Jupiter, Saturn, Uranus, Neptune)
trait Equals

An interface containing operations for equality.

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

final abstract 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.

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.

Companion
object
object Float extends AnyValCompanion
Companion
class
object Function

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

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

trait Function0[@specialized +R] extends AnyRef

A function of 0 parameters.

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())
}
object Function1
Companion
class
@implicitNotFound(msg = "No implicit view available from ${T1} => ${R}.")
trait Function1[@specialized -T1, @specialized +R] extends AnyRef

A function of 1 parameter.

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.

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

A function of 10 parameters.

A function of 10 parameters.

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

A function of 11 parameters.

A function of 11 parameters.

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

A function of 12 parameters.

A function of 12 parameters.

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

A function of 13 parameters.

A function of 13 parameters.

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

A function of 14 parameters.

A function of 14 parameters.

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

A function of 15 parameters.

A function of 15 parameters.

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

A function of 16 parameters.

A function of 16 parameters.

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

A function of 17 parameters.

A function of 17 parameters.

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

A function of 18 parameters.

A function of 18 parameters.

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

A function of 19 parameters.

A function of 19 parameters.

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

A function of 2 parameters.

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

A function of 20 parameters.

A function of 20 parameters.

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

A function of 21 parameters.

A function of 21 parameters.

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

A function of 22 parameters.

A function of 22 parameters.

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

A function of 3 parameters.

A function of 3 parameters.

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

A function of 4 parameters.

A function of 4 parameters.

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

A function of 5 parameters.

A function of 5 parameters.

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

A function of 6 parameters.

A function of 6 parameters.

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

A function of 7 parameters.

A function of 7 parameters.

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

A function of 8 parameters.

A function of 8 parameters.

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

A function of 9 parameters.

A function of 9 parameters.

object IArray

An immutable array.

An immutable array. An IArray[T] has the same representation as an Array[T], but it cannot be updated. Unlike regular arrays, immutable arrays are covariant.

final abstract class Int extends AnyVal

Int, a 32-bit signed integer (equivalent to Java's int primitive type) is a subtype of scala.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.

Companion
object
object Int extends AnyValCompanion
Companion
class
final abstract class Long extends AnyVal

Long, a 64-bit signed integer (equivalent to Java's long primitive type) is a subtype of scala.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.

Companion
object
object Long extends AnyValCompanion
Companion
class
final class MatchError(obj: Any) extends RuntimeException

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

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

sealed trait NonEmptyTuple extends Tuple

Tuple of arbitrary non-zero arity

Tuple of arbitrary non-zero arity

@SerialVersionUID(5066590221178148012L)
case object None extends Option[Nothing]

This case object represents non-existent values.

This case object represents non-existent values.

final class NotImplementedError(msg: String) extends Error

Throwing this exception can be a temporary replacement for a method body that remains to be implemented.

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.???.

object Option
Companion
class
@SerialVersionUID(-114498752079829388L)
sealed abstract class Option[+A] extends IterableOnce[A] with Product with Serializable

Represents optional values.

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")
}
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.

Companion
object
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.

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)
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 | Function1.UnliftOps#unlift or Function.unlift | Predef.identity | Function1.UnliftOps#unlift | | from an extractor | { case extractor(x) => x } | extractor.unapply _ | Predef.identity |  

Companion
object

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

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 }
Companion
class

Marker trait for polymorphic function types.

Marker trait for polymorphic function types.

This is the only trait that can be refined with a polymorphic method, as long as that method is called apply, e.g.: PolyFunction { def apply[T_1, ..., T_M](x_1: P_1, ..., x_N: P_N): R } This type will be erased to FunctionN.

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

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 and scala.collection.immutable.Set.

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.

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.

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.

object Product1
Companion
class
trait Product1[@specialized(Int, Long, Double) +T1] extends Product

Product1 is a Cartesian product of 1 component.

Product1 is a Cartesian product of 1 component.

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

Product10 is a Cartesian product of 10 components.

Product10 is a Cartesian product of 10 components.

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

Product11 is a Cartesian product of 11 components.

Product11 is a Cartesian product of 11 components.

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

Product12 is a Cartesian product of 12 components.

Product12 is a Cartesian product of 12 components.

Companion
object
object Product13
Companion
class
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.

Product13 is a Cartesian product of 13 components.

Companion
object
object Product14
Companion
class
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.

Product14 is a Cartesian product of 14 components.

Companion
object
object Product15
Companion
class
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.

Product15 is a Cartesian product of 15 components.

Companion
object
object Product16
Companion
class
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.

Product16 is a Cartesian product of 16 components.

Companion
object
object Product17
Companion
class
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.

Product17 is a Cartesian product of 17 components.

Companion
object
object Product18
Companion
class
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.

Product18 is a Cartesian product of 18 components.

Companion
object
object Product19
Companion
class
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.

Product19 is a Cartesian product of 19 components.

Companion
object
object Product2
Companion
class
trait Product2[@specialized(Int, Long, Double) +T1, @specialized(Int, Long, Double) +T2] extends Product

Product2 is a Cartesian product of 2 components.

Product2 is a Cartesian product of 2 components.

Companion
object
object Product20
Companion
class
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.

Product20 is a Cartesian product of 20 components.

Companion
object
object Product21
Companion
class
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.

Product21 is a Cartesian product of 21 components.

Companion
object
object Product22
Companion
class
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.

Product22 is a Cartesian product of 22 components.

Companion
object
object Product3
Companion
class
trait Product3[+T1, +T2, +T3] extends Product

Product3 is a Cartesian product of 3 components.

Product3 is a Cartesian product of 3 components.

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

Product4 is a Cartesian product of 4 components.

Product4 is a Cartesian product of 4 components.

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

Product5 is a Cartesian product of 5 components.

Product5 is a Cartesian product of 5 components.

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

Product6 is a Cartesian product of 6 components.

Product6 is a Cartesian product of 6 components.

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

Product7 is a Cartesian product of 7 components.

Product7 is a Cartesian product of 7 components.

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

Product8 is a Cartesian product of 8 components.

Product8 is a Cartesian product of 8 components.

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

Product9 is a Cartesian product of 9 components.

Product9 is a Cartesian product of 9 components.

Companion
object
case class ScalaReflectionException(msg: String) extends Exception

An exception that indicates an error during Scala reflection

An exception that indicates an error during Scala reflection

trait Selectable

A marker trait for objects that support structural selection via selectDynamic and applyDynamic

A marker trait for objects that support structural selection via selectDynamic and applyDynamic

Implementation classes should define, or make available as extension methods, the following two method signatures:

def selectDynamic(name: String): Any def applyDynamic(name: String)(args: Any*): Any =

selectDynamic is invoked for simple selections v.m, whereas applyDynamic is invoked for selections with arguments v.m(...). If there's only one kind of selection, the method supporting the other may be omitted. The applyDynamic can also have a second parameter list of java.lang.Class arguments, i.e. it may alternatively have the signature

def applyDynamic(name: String, paramClasses: Class[_]*)(args: Any*): Any

In this case the call will synthesize Class arguments for the erasure of all formal parameter types of the method in the structural type.

Companion
object
object Selectable
Companion
class
@deprecatedInheritance("Scheduled for being final in the future", "2.13.0")

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

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.

See also
final abstract class Short extends AnyVal

Short, a 16-bit signed integer (equivalent to Java's short primitive type) is a subtype of scala.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.

Companion
object
object Short extends AnyValCompanion
Companion
class
@SerialVersionUID(1234815782226070388L)
final case class Some[+A](value: A) extends Option[A]

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

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

A common supertype for companions of specializable types.

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

Companion
object
Companion
class
case class StringContext(parts: String*)

This class provides the basic mechanism to do String Interpolation.

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.

Value Params
parts

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

Companion
object
Companion
class
final class Symbol extends Serializable

This class provides a simple way to get unique objects for equal strings.

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").

Companion
object
Companion
class
sealed trait Tuple extends Product

Tuple of arbitrary arity

Tuple of arbitrary arity

Companion
object
object Tuple
Companion
class
final case class Tuple1[@specialized(Int, Long, Double) +T1](_1: T1) extends Product1[T1]

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

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

Value Params
_1

Element 1 of this Tuple1

Constructor

Create a new tuple with 1 elements.

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]

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

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

Value Params
_1

Element 1 of this Tuple10

_10

Element 10 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

Constructor

Create a new tuple with 10 elements. Note that it is more idiomatic to create a Tuple10 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10)

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]

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

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

Value Params
_1

Element 1 of this Tuple11

_10

Element 10 of this Tuple11

_11

Element 11 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

Constructor

Create a new tuple with 11 elements. Note that it is more idiomatic to create a Tuple11 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11)

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]

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

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

Value Params
_1

Element 1 of this Tuple12

_10

Element 10 of this Tuple12

_11

Element 11 of this Tuple12

_12

Element 12 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

Constructor

Create a new tuple with 12 elements. Note that it is more idiomatic to create a Tuple12 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12)

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]

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

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

Value Params
_1

Element 1 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

_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

Constructor

Create a new tuple with 13 elements. Note that it is more idiomatic to create a Tuple13 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13)

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]

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

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

Value Params
_1

Element 1 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

_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

Constructor

Create a new tuple with 14 elements. Note that it is more idiomatic to create a Tuple14 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14)

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]

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

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

Value Params
_1

Element 1 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

_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

Constructor

Create a new tuple with 15 elements. Note that it is more idiomatic to create a Tuple15 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15)

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]

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

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

Value Params
_1

Element 1 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

_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

Constructor

Create a new tuple with 16 elements. Note that it is more idiomatic to create a Tuple16 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15, t16)

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]

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

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

Value Params
_1

Element 1 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

_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

Constructor

Create a new tuple with 17 elements. Note that it is more idiomatic to create a Tuple17 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15, t16, t17)

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]

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

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

Value Params
_1

Element 1 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

_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

Constructor

Create a new tuple with 18 elements. Note that it is more idiomatic to create a Tuple18 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15, t16, t17, t18)

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]

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

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

Value Params
_1

Element 1 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

_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

Constructor

Create a new tuple with 19 elements. Note that it is more idiomatic to create a Tuple19 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15, t16, t17, t18, t19)

final case class Tuple2[@specialized(Int, Long, Double, Char, Boolean) +T1, @specialized(Int, Long, Double, Char, Boolean) +T2](_1: T1, _2: T2) extends Product2[T1, T2]

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

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

Value Params
_1

Element 1 of this Tuple2

_2

Element 2 of this Tuple2

Constructor

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

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]

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

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

Value Params
_1

Element 1 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

_2

Element 2 of this Tuple20

_20

Element 20 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

Constructor

Create a new tuple with 20 elements. Note that it is more idiomatic to create a Tuple20 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15, t16, t17, t18, t19, t20)

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]

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

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

Value Params
_1

Element 1 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

_2

Element 2 of this Tuple21

_20

Element 20 of this Tuple21

_21

Element 21 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

Constructor

Create a new tuple with 21 elements. Note that it is more idiomatic to create a Tuple21 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15, t16, t17, t18, t19, t20, t21)

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]

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

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

Value Params
_1

Element 1 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

_2

Element 2 of this Tuple22

_20

Element 20 of this Tuple22

_21

Element 21 of this Tuple22

_22

Element 22 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

Constructor

Create a new tuple with 22 elements. Note that it is more idiomatic to create a Tuple22 via (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15, t16, t17, t18, t19, t20, t21, t22)

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

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

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

Value Params
_1

Element 1 of this Tuple3

_2

Element 2 of this Tuple3

_3

Element 3 of this Tuple3

Constructor

Create a new tuple with 3 elements. Note that it is more idiomatic to create a Tuple3 via (t1, t2, t3)

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

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

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

Value Params
_1

Element 1 of this Tuple4

_2

Element 2 of this Tuple4

_3

Element 3 of this Tuple4

_4

Element 4 of this Tuple4

Constructor

Create a new tuple with 4 elements. Note that it is more idiomatic to create a Tuple4 via (t1, t2, t3, t4)

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]

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

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

Value Params
_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

Constructor

Create a new tuple with 5 elements. Note that it is more idiomatic to create a Tuple5 via (t1, t2, t3, t4, t5)

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]

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

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

Value Params
_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

Constructor

Create a new tuple with 6 elements. Note that it is more idiomatic to create a Tuple6 via (t1, t2, t3, t4, t5, t6)

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]

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

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

Value Params
_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

Constructor

Create a new tuple with 7 elements. Note that it is more idiomatic to create a Tuple7 via (t1, t2, t3, t4, t5, t6, t7)

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]

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

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

Value Params
_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

Constructor

Create a new tuple with 8 elements. Note that it is more idiomatic to create a Tuple8 via (t1, t2, t3, t4, t5, t6, t7, t8)

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]

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

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

Value Params
_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

Constructor

Create a new tuple with 9 elements. Note that it is more idiomatic to create a Tuple9 via (t1, t2, t3, t4, t5, t6, t7, t8, t9)

final case class UninitializedFieldError(msg: String) extends RuntimeException

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

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.

final abstract class Unit extends AnyVal

Unit is a subtype of scala.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.

Companion
object
@compileTimeOnly("`Unit` companion object is not allowed in source; instead, use `()` for the unit value")
object Unit extends AnyValCompanion
Companion
class
@implicitNotFound(msg = "No singleton value available for ${T}.")
final class ValueOf[T](val value: T) extends AnyVal

ValueOf[T] provides the unique value of the type T where T is a type which has a single inhabitant.

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].

@getter @setter @beanGetter @beanSetter @field @deprecatedInheritance("Scheduled for being final in the future", "2.13.0")
class deprecated(message: String, since: String) extends StaticAnnotation

An annotation that designates that a definition is deprecated.

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 the future. (A deprecated element might be kept longer to ease migration, but developers should not rely on this.)

Value Params
message

the message to print during compilation if the definition is accessed

since

a string identifying the first version in which the definition was deprecated

See also
final class deprecatedInheritance(message: String, since: String) extends StaticAnnotation

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

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
//                   ^
Value Params
message

the message to print during compilation if the class was sub-classed

since

a string identifying the first version in which inheritance was deprecated

See also
@param @deprecatedInheritance("Scheduled for being final in the future", "2.13.0")
class deprecatedName(name: String, since: String) extends StaticAnnotation

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

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)
         ^
See also
@getter @setter @beanGetter @beanSetter @deprecatedInheritance("Scheduled for being final in the future", "2.13.0")
class deprecatedOverriding(message: String, since: String) extends StaticAnnotation

An annotation that designates that overriding a member is deprecated.

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
//              ^
Value Params
message

the message to print during compilation if the member was overridden

since

a string identifying the first version in which overriding was deprecated

See also
@deprecatedInheritance("Scheduled for being final in the future", "2.13.0")
class inline extends StaticAnnotation

An annotation for methods that the optimizer should inline.

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
object language

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

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:

class main extends Annotation

An annotation that designates a main function

An annotation that designates a main function

@deprecatedInheritance("Scheduled for being final in the future", "2.13.0")
class native extends StaticAnnotation

Marker for native methods.

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).

final class noinline extends StaticAnnotation

An annotation for methods that the optimizer should not inline.

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(group: SpecializedGroup) extends StaticAnnotation

Annotate type parameters on which code should be automatically specialized.

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] ..
final class throws[T <: Throwable](cause: String) extends StaticAnnotation

Annotation for specifying the exceptions thrown by a method.

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()
}
final class transient extends StaticAnnotation
final class unchecked extends Annotation

An annotation to designate that the annotated entity should not be considered for additional compiler checks.

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 and reachability 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 }
}
final class volatile extends StaticAnnotation

Deprecated classlikes

@deprecated("DelayedInit semantics can be surprising. Support for `App` will continue. See the release notes for more details: https://github.com/scala/scala/releases/tag/v2.11.0", "2.11.0")

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

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

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

Example:

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

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

object Test extends App {
  val c = new C
}

Should result in the following being printed:

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

"Delayed Initialization" subsection of the Scala Language Specification (section 5.1)

Deprecated
@deprecated("Explicitly override hashCode, equals and toString instead.", "2.13.0")
trait Proxy

This class implements a simple proxy that forwards all calls to the public, non-final methods defined in class Any to another object self.

This class implements a simple proxy that forwards all calls to the public, non-final methods defined in class Any to another object self. Those methods are:

def hashCode(): Int
def equals(other: Any): Boolean
def toString(): String

Note: forwarding methods in this way will most likely create an asymmetric equals method, which is not generally recommended.

Companion
object
Deprecated
@deprecated("All members of this object are deprecated.", "2.13.0")
object Proxy
Companion
class
Deprecated
@deprecated("will be removed in a future release", since = "2.12.7")

This class represents uninitialized variable/value errors.

This class represents uninitialized variable/value errors.

Deprecated
[Since version 2.12.7]

Types

type ::[+A] = ::[A]
type BigInt = BigInt
type Either[+A, +B] = Either[A, B]

A tuple of 0 elements

A tuple of 0 elements

type Equiv[T] = Equiv[T]
type Error = Error
type Fractional[T] = Fractional[T]
opaque type IArray[+T]
@migration("scala.IndexedSeq is now scala.collection.immutable.IndexedSeq instead of scala.collection.IndexedSeq", "2.13.0")
type IndexedSeq[+A] = IndexedSeq[A]
type Integral[T] = Integral[T]
type Iterable[+A] = Iterable[A]
type Iterator[+A] = Iterator[A]
type LazyList[+A] = LazyList[A]
type Left[+A, +B] = Left[A, B]
type List[+A] = List[A]
type Numeric[T] = Numeric[T]
type Ordered[T] = Ordered[T]
type Ordering[T] = Ordering[T]
type Range = Range
type Right[+A, +B] = Right[A, B]
@migration("scala.Seq is now scala.collection.immutable.Seq instead of scala.collection.Seq", "2.13.0")
type Seq[+A] = Seq[A]
type Vector[+A] = Vector[A]

Deprecated types

@deprecated("Use scala.collection.BufferedIterator instead of scala.BufferedIterator", "2.13.0")
Deprecated
@deprecated("Use LazyList instead of Stream", "2.13.0")
type Stream[+A] = Stream[A]
Deprecated
@deprecated("Use Iterable instead of Traversable", "2.13.0")
type Traversable[+A] = Iterable[A]
Deprecated
@deprecated("Use IterableOnce instead of TraversableOnce", "2.13.0")
Deprecated

Value members

Deprecated fields

@deprecated("Use LazyList instead of Stream", "2.13.0")
Deprecated
@deprecated("Use Iterable instead of Traversable", "2.13.0")
Deprecated