scala (original) (raw)

This package object contains primitives for concurrent and parallel programming.

Guide

A more detailed guide to Futures and Promises, including discussion and examples can be found at https://docs.scala-lang.org/overviews/core/futures.html.

Common Imports

When working with Futures, you will often find that importing the whole concurrent package is convenient:

import scala.concurrent._

When using things like Futures, it is often required to have an implicit ExecutionContext in scope. The general advice for these implicits are as follows.

If the code in question is a class or method definition, and no ExecutionContext is available, request one from the caller by adding an implicit parameter list:

def myMethod(myParam: MyType)(implicit ec: ExecutionContext) = …
//Or
class MyClass(myParam: MyType)(implicit ec: ExecutionContext) { … }

This allows the caller of the method, or creator of the instance of the class, to decide which ExecutionContext should be used.

For typical REPL usage and experimentation, importing the global ExecutionContext is often desired.

import scala.concurrent.ExcutionContext.Implicits.global

Specifying Durations

Operations often require a duration to be specified. A duration DSL is available to make defining these easier:

import scala.concurrent.duration._
val d: Duration = 10.seconds

Using Futures For Non-blocking Computation

Basic use of futures is easy with the factory method on Future, which executes a provided function asynchronously, handing you back a future result of that function without blocking the current thread. In order to create the Future you will need either an implicit or explicit ExecutionContext to be provided:

import scala.concurrent._
import ExecutionContext.Implicits.global  // implicit execution context

val firstZebra: Future[Int] = Future {
 val words = Files.readAllLines("/etc/dictionaries-common/words").asScala
 words.indexOfSlice("zebra")
}

Avoid Blocking

Although blocking is possible in order to await results (with a mandatory timeout duration):

import scala.concurrent.duration._
Await.result(firstZebra, 10.seconds)

and although this is sometimes necessary to do, in particular for testing purposes, blocking in general is discouraged when working with Futures and concurrency in order to avoid potential deadlocks and improve performance. Instead, use callbacks or combinators to remain in the future domain:

val animalRange: Future[Int] = for {
 aardvark <- firstAardvark
 zebra <- firstZebra
} yield zebra - aardvark

animalRange.onSuccess {
 case x if x > 500000 => println("It's a long way from Aardvark to Zebra")
}

Attributes

The jdk package contains utilities to interact with JDK classes.

This packages offers a number of converters, that are able to wrap or copy types from the scala library to equivalent types in the JDK class library and vice versa:

- CollectionConverters, converting collections like scala.collection.Seq, scala.collection.Map, scala.collection.Set, scala.collection.mutable.Buffer, scala.collection.Iterator and scala.collection.Iterable to their JDK counterparts - OptionConverters, converting between Option and java.util.Optional and primitive variations - StreamConverters, to create JDK Streams from scala collections - DurationConverters, for conversions between scala scala.concurrent.duration.FiniteDuration and java.time.Duration - FunctionConverters, from scala Functions to java java.util.function.Function, java.util.function.UnaryOperator, java.util.function.Consumer and java.util.function.Predicate, as well as primitive variations and Bi-variations.

By convention, converters that wrap an object to provide a different interface to the same underlying data structure use .asScala and .asJava extension methods, whereas converters that copy the underlying data structure use .toScala and .toJava.

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

Additionally, this package offers Accumulators, capable of efficiently traversing JDK Streams.

Attributes

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.

Attributes

See also

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.

Attributes

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 parameters

From

a type which is proved a subtype of To

a type which is proved a supertype of From

Attributes

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

Source

typeConstraints.scala

Supertypes

Known subtypes

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.

Type parameters

From

a type which is proved equal to To

a type which is proved equal to From

Attributes

See also

<:< 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.
}

Source

typeConstraints.scala

Supertypes

class From <:< To

trait From => To

Show all

Class Any is the root of the Scala class hierarchy.

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.

Attributes

The super-type of all types.

Attributes

Class AnyRef is the root class of all reference types.

Class AnyRef is the root class of all reference types. All types except the value types descend from this class.

Attributes

Known subtypes

trait () => R

trait T1 => R

class From <:< To

class From =:= To

trait MapOps[K, V, CC, C]

trait Map[K, V]

trait MapOps[K, V, CC, C]

trait Map[K, V]

class Id[K, V]

class ::[A]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10) => R

class AbstractFunction10[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11) => R

class AbstractFunction11[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12) => R

class AbstractFunction12[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13) => R

class AbstractFunction13[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14) => R

class AbstractFunction14[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15) => R

class AbstractFunction15[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16) => R

class AbstractFunction16[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17) => R

class AbstractFunction17[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18) => R

class AbstractFunction18[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19) => R

class AbstractFunction19[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, R]

trait (T1, T2) => R

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20) => R

class AbstractFunction20[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21) => R

class AbstractFunction21[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, R]

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22) => R

class AbstractFunction22[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22, R]

trait (T1, T2, T3) => R

trait (T1, T2, T3, T4) => R

trait (T1, T2, T3, T4, T5) => R

trait (T1, T2, T3, T4, T5, T6) => R

trait (T1, T2, T3, T4, T5, T6, T7) => R

trait (T1, T2, T3, T4, T5, T6, T7, T8) => R

trait (T1, T2, T3, T4, T5, T6, T7, T8, T9) => R

Show all

AnyVal is the root class of all value types, which describe values not implemented as objects in the underlying host system.

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:

The subrange types are scala.Byte, scala.Short, and scala.Char.
The integer types include the subrange types as well as scala.Int and scala.Long.
The floating point types are scala.Float and scala.Double.

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.

Attributes

Supertypes

Known subtypes

class Ops[T1, T2]

class Ops[T1, T2, T3]

Show all

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.

In Scala 3, the DelayedInit feature was dropped. App exists only in a limited form that also does not support command line arguments and will be deprecated in the future.

@main methods are the recommended scheme to generate programs that can be invoked from the command line in Scala 3.

@main def runMyProgram(args: String*): Unit = {
  // your program here
}

If programs need to cross-build between Scala 2 and Scala 3, it is recommended to use an explicit main method:

object Main {
  def main(args: Array[String]): Unit = {
    // your program here
  }
}

Attributes

Source

App.scala

Supertypes

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).

Attributes

Companion

class

Source

Array.scala

Supertypes

Self type

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.

Attributes

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.

Companion

object

Source

Array.scala

Supertypes

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.

Attributes

Companion

object

Source

Boolean.scala

Supertypes

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.

Attributes

Companion

object

Source

Byte.scala

Supertypes

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

Attributes

Companion

object

Source

CanEqual.scala

Supertypes

Known subtypes

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.

Attributes

Companion

trait

Source

CanEqual.scala

Supertypes

Self type

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.

Attributes

Companion

object

Source

Char.scala

Supertypes

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)

Attributes

Source

Console.scala

Supertypes

Self type

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.

Attributes

Source

Conversion.scala

Supertypes

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.

Attributes

Companion

object

Source

Double.scala

Supertypes

A type for which there is always an implicit value.

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)

Defining direct or indirect subclasses of this trait is only possible if the language feature dynamics is enabled.

Attributes

Source

Dynamic.scala

Supertypes

A tuple of 0 elements.

Attributes

Source

Tuple.scala

Supertypes

Self type

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 parameters

initial

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

Attributes

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)

Source

Enumeration.scala

Supertypes

Known subtypes

Self type

An interface containing operations for equality.

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

Attributes

Source

Equals.scala

Supertypes

Known subtypes

trait Map[K, V]

class ::[A]

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19)

class (T1, T2)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22)

class (T1, T2, T3)

class (T1, T2, T3, T4)

trait Product5[T1, T2, T3, T4, T5]

class (T1, T2, T3, T4, T5)

trait Product6[T1, T2, T3, T4, T5, T6]

class (T1, T2, T3, T4, T5, T6)

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

class (T1, T2, T3, T4, T5, T6, T7)

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

class (T1, T2, T3, T4, T5, T6, T7, T8)

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

class (T1, T2, T3, T4, T5, T6, T7, T8, T9)

class H *: T

Show all

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.

Attributes

Companion

object

Source

Float.scala

Supertypes

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

Attributes

Source

Function.scala

Supertypes

Self type

A function of 0 parameters.

In the following example, the definition of greeting is shorthand, conceptually, for the anonymous class definition anonfun0, although the implementation details of how the function value is constructed may differ:

object Main extends App {
  val name = "world"
  val greeting = () => s"hello, $name"

  val anonfun0 = new Function0[String] {
    def apply(): String = s"hello, $name"
  }
  assert(greeting() == anonfun0())
}

Attributes

Source

Function0.scala

Supertypes

Known subtypes

Self type

A function of 1 parameter.

In the following example, the definition of succ is shorthand, conceptually, for the anonymous class definition anonfun1, although the implementation details of how the function value is constructed may differ:

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.

Attributes

Companion

object

Source

Function1.scala

Supertypes

Known subtypes

class From <:< To

class From =:= To

trait MapOps[K, V, CC, C]

trait Map[K, V]

trait MapOps[K, V, CC, C]

trait Map[K, V]

class Id[K, V]

class ::[A]

Show all

Self type

A function of 10 parameters.

Attributes

Source

Function10.scala

Supertypes

Known subtypes

class AbstractFunction10[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10) => R

A function of 11 parameters.

Attributes

Source

Function11.scala

Supertypes

Known subtypes

class AbstractFunction11[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11) => R

A function of 12 parameters.

Attributes

Source

Function12.scala

Supertypes

Known subtypes

class AbstractFunction12[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12) => R

A function of 13 parameters.

Attributes

Source

Function13.scala

Supertypes

Known subtypes

class AbstractFunction13[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13) => R

A function of 14 parameters.

Attributes

Source

Function14.scala

Supertypes

Known subtypes

class AbstractFunction14[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14) => R

A function of 15 parameters.

Attributes

Source

Function15.scala

Supertypes

Known subtypes

class AbstractFunction15[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15) => R

A function of 16 parameters.

Attributes

Source

Function16.scala

Supertypes

Known subtypes

class AbstractFunction16[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16) => R

A function of 17 parameters.

Attributes

Source

Function17.scala

Supertypes

Known subtypes

class AbstractFunction17[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17) => R

A function of 18 parameters.

Attributes

Source

Function18.scala

Supertypes

Known subtypes

class AbstractFunction18[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18) => R

A function of 19 parameters.

Attributes

Source

Function19.scala

Supertypes

Known subtypes

class AbstractFunction19[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19) => R

A function of 2 parameters.

In the following example, the definition of max is shorthand, conceptually, for the anonymous class definition anonfun2, although the implementation details of how the function value is constructed may differ:

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))
}

Attributes

Source

Function2.scala

Supertypes

Known subtypes

Self type

A function of 20 parameters.

Attributes

Source

Function20.scala

Supertypes

Known subtypes

class AbstractFunction20[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20) => R

A function of 21 parameters.

Attributes

Source

Function21.scala

Supertypes

Known subtypes

class AbstractFunction21[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21) => R

A function of 22 parameters.

Attributes

Source

Function22.scala

Supertypes

Known subtypes

class AbstractFunction22[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22, R]

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21, T22) => R

A function of 3 parameters.

Attributes

Source

Function3.scala

Supertypes

Known subtypes

Self type

A function of 4 parameters.

Attributes

Source

Function4.scala

Supertypes

Known subtypes

Self type

A function of 5 parameters.

Attributes

Source

Function5.scala

Supertypes

Known subtypes

Self type

(T1, T2, T3, T4, T5) => R

A function of 6 parameters.

Attributes

Source

Function6.scala

Supertypes

Known subtypes

Self type

(T1, T2, T3, T4, T5, T6) => R

A function of 7 parameters.

Attributes

Source

Function7.scala

Supertypes

Known subtypes

Self type

(T1, T2, T3, T4, T5, T6, T7) => R

A function of 8 parameters.

Attributes

Source

Function8.scala

Supertypes

Known subtypes

Self type

(T1, T2, T3, T4, T5, T6, T7, T8) => R

A function of 9 parameters.

Attributes

Source

Function9.scala

Supertypes

Known subtypes

Self type

(T1, T2, T3, T4, T5, T6, T7, T8, T9) => R

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.

Attributes

Source

IArray.scala

Supertypes

Self type

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.

Attributes

Companion

object

Source

Int.scala

Supertypes

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.

Attributes

Companion

object

Source

Long.scala

Supertypes

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

Attributes

Source

MatchError.scala

Supertypes

The base trait of types that can be safely pattern matched against.

Separate from NamedTuple object so that we can match on the opaque type NamedTuple.

Attributes

Source

NamedTuple.scala

Supertypes

Self type

Tuple of arbitrary non-zero arity

Attributes

Source

Tuple.scala

Supertypes

Known subtypes

This case object represents non-existent values.

Attributes

Source

Option.scala

Supertypes

Self type

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.???.

Attributes

Source

NotImplementedError.scala

Supertypes

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.

Attributes

Supertypes

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

Null is the type of the null literal. It is a subtype of every type except those of value classes. Value classes are subclasses of AnyVal, which includes primitive types such as Int, Boolean, and user-defined value classes.

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.

Attributes

Supertypes

Represents optional values.

Represents optional values. Instances of Option are either an instance of someortheobjectsome or the object someortheobjectnone.

The most idiomatic way to use an $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 noneisreturnedfrom‘request.getParameter‘,theentireexpressionresultsinnone is returned from request.getParameter, the entire expression results in noneisreturnedfrom‘request.getParameter‘,theentireexpressionresultsinnone

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

These are useful methods that exist for both someandsome and someandnone. - 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 $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 optiontobecomeoption to become optiontobecomenone and $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")
}

Attributes

Note

Many of the methods in here are duplicative with those in the Iterable 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

Source

Option.scala

Supertypes

Known subtypes

Self type

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 x => x / 0 }   // ArithmeticException: / by zero

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 usual way to respect this contract is to call applyOrElse, which is expected to be more efficient than calling both isDefinedAt and apply.

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
def isEven(n: Int) = n % 2 == 0
val eveningNews: PartialFunction[Int, String] = {
  case x if isEven(x) => s"$x is even"
}

// The method collect is described as "filter + map"
// because it uses a PartialFunction to select elements
// to which the function is applied.
val evenNumbers = sample.collect(eveningNews)

val oddlyEnough: PartialFunction[Int, String] = {
  case x if !isEven(x) => s"$x is odd"
}

// The method orElse allows chaining another PartialFunction
// to handle input outside the declared domain.
val numbers = sample.map(eveningNews orElse oddlyEnough)

// same as
val numbers = sample.map(n => eveningNews.applyOrElse(n, oddlyEnough))

val half: PartialFunction[Int, Int] = {
  case x if isEven(x) => x / 2
}

// Calculating the domain of a composition can be expensive.
val oddByHalf = half.andThen(oddlyEnough)

// Invokes `half.apply` on even elements!
val oddBalls = sample.filter(oddByHalf.isDefinedAt)

// Better than filter(oddByHalf.isDefinedAt).map(oddByHalf)
val oddBalls = sample.collect(oddByHalf)

// Providing "default" values.
val oddsAndEnds = sample.map(n => oddByHalf.applyOrElse(n, (i: Int) => s"[$i]"))

Attributes

Note

Companion

object

Source

PartialFunction.scala

Supertypes

Known subtypes

trait MapOps[K, V, CC, C]

trait Map[K, V]

trait MapOps[K, V, CC, C]

trait Map[K, V]

class Id[K, V]

class ::[A]

Show all

Self type

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 }

Attributes

Companion

trait

Source

PartialFunction.scala

Supertypes

Self type

Marker trait for polymorphic function types.

This trait can only 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 } Exactly one term argument list is expected. The term argument list may be contextual.

This type will be erased to FunctionN or FunctionXXL.

Attributes

Source

PolyFunction.scala

Supertypes

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.

Attributes

Source

Predef.scala

Supertypes

Self type

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.

Attributes

Source

Product.scala