Packages

  • package root

    This is the documentation for the Scala standard library.

    This is the documentation for the Scala standard library.

    Package structure

    The scala package contains core types like Int, Float, Array or Option which are accessible in all Scala compilation units without explicit qualification or imports.

    Notable packages include:

    Other packages exist. See the complete list on the right.

    Additional parts of the standard library are shipped as separate libraries. These include:

    Automatic imports

    Identifiers in the scala package and the scala.Predef object are always in scope by default.

    Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example, List is an alias for scala.collection.immutable.List.

    Other aliases refer to classes provided by the underlying platform. For example, on the JVM, String is an alias for java.lang.String.

    Definition Classes
    root
  • package scala

    Core Scala types.

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

    Definition Classes
    root
  • package concurrent

    This package object contains primitives for concurrent and parallel programming.

    This package object contains primitives for concurrent and parallel programming.

    Guide

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

    Common Imports

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

    import scala.concurrent._

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

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

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

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

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

    import scala.concurrent.ExcutionContext.Implicits.global

    Specifying Durations

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

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

    Using Futures For Non-blocking Computation

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

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

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

    Avoid Blocking

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

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

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

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

animalRange.onSuccess {
  case x if x > 500000 => println("It's a long way from Aardvark to Zebra")
}
    Definition Classes
    scala
  • package duration
    Definition Classes
    concurrent
  • Deadline
  • DoubleMult
  • Duration
  • DurationConversions
  • DurationDouble
  • DurationInt
  • DurationLong
  • FiniteDuration
  • IntMult
  • LongMult
  • fromNow
  • span

object Duration extends java.io.Serializable

Ordering
  1. Alphabetic
  2. By Inheritance
Inherited
  1. Duration
  2. Serializable
  3. AnyRef
  4. Any
  1. Hide All
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Visibility
  1. Public
  2. Protected

Type Members

  1. sealed abstract class Infinite extends Duration

Value Members

  1. val Inf: Infinite

    Infinite duration: greater than any other (apart from Undefined) and not equal to any other but itself.

    Infinite duration: greater than any other (apart from Undefined) and not equal to any other but itself. This value closely corresponds to Double.PositiveInfinity, matching its semantics in arithmetic operations.

  2. val MinusInf: Infinite

    Infinite duration: less than any other and not equal to any other but itself.

    Infinite duration: less than any other and not equal to any other but itself. This value closely corresponds to Double.NegativeInfinity, matching its semantics in arithmetic operations.

  3. val Undefined: Infinite

    The Undefined value corresponds closely to Double.NaN:

    The Undefined value corresponds closely to Double.NaN:

    • it is the result of otherwise invalid operations
    • it does not equal itself (according to equals())
    • it compares greater than any other Duration apart from itself (for which compare returns 0)

    The particular comparison semantics mirror those of Double.NaN.

    Use eq when checking an input of a method against this value.

  4. val Zero: FiniteDuration

    Preconstructed value of 0.days.

  5. def apply(s: String): Duration

    Parse String into Duration.

    Parse String into Duration. Format is "<length><unit>", where whitespace is allowed before, between and after the parts. Infinities are designated by "Inf", "PlusInf", "+Inf", "Duration.Inf" and "-Inf", "MinusInf" or "Duration.MinusInf". Undefined is designated by "Duration.Undefined".

    Exceptions thrown

    NumberFormatException if format is not parsable

  6. def apply(length: Long, unit: String): FiniteDuration

    Construct a finite duration from the given length and time unit, where the latter is looked up in a list of string representation.

    Construct a finite duration from the given length and time unit, where the latter is looked up in a list of string representation. Valid choices are:

    d, day, h, hr, hour, m, min, minute, s, sec, second, ms, milli, millisecond, µs, micro, microsecond, ns, nano, nanosecond and their pluralized forms (for every but the first mentioned form of each unit, i.e. no "ds", but "days").

  7. def apply(length: Long, unit: TimeUnit): FiniteDuration

    Construct a finite duration from the given length and time unit.

    Construct a finite duration from the given length and time unit. The unit given is retained throughout calculations as long as possible, so that it can be retrieved later.

  8. def apply(length: Double, unit: TimeUnit): Duration

    Construct a Duration from the given length and unit.

    Construct a Duration from the given length and unit. Observe that nanosecond precision may be lost if

    • the unit is NANOSECONDS
    • and the length has an absolute value greater than 2^53

    Infinite inputs (and NaN) are converted into Duration.Inf, Duration.MinusInf and Duration.Undefined, respectively.

    Exceptions thrown

    IllegalArgumentException if the length was finite but the resulting duration cannot be expressed as a FiniteDuration

  9. def create(s: String): Duration

    Parse String into Duration.

    Parse String into Duration. Format is "<length><unit>", where whitespace is allowed before, between and after the parts. Infinities are designated by "Inf", "PlusInf", "+Inf" and "-Inf" or "MinusInf".

    Exceptions thrown

    NumberFormatException if format is not parsable

  10. def create(length: Long, unit: String): FiniteDuration

    Construct a finite duration from the given length and time unit, where the latter is looked up in a list of string representation.

    Construct a finite duration from the given length and time unit, where the latter is looked up in a list of string representation. Valid choices are:

    d, day, h, hour, min, minute, s, sec, second, ms, milli, millisecond, µs, micro, microsecond, ns, nano, nanosecond and their pluralized forms (for every but the first mentioned form of each unit, i.e. no "ds", but "days").

  11. def create(length: Double, unit: TimeUnit): Duration

    Construct a Duration from the given length and unit.

    Construct a Duration from the given length and unit. Observe that nanosecond precision may be lost if

    • the unit is NANOSECONDS
    • and the length has an absolute value greater than 2^53

    Infinite inputs (and NaN) are converted into Duration.Inf, Duration.MinusInf and Duration.Undefined, respectively.

    Exceptions thrown

    IllegalArgumentException if the length was finite but the resulting duration cannot be expressed as a FiniteDuration

  12. def create(length: Long, unit: TimeUnit): FiniteDuration

    Construct a finite duration from the given length and time unit.

    Construct a finite duration from the given length and time unit. The unit given is retained throughout calculations as long as possible, so that it can be retrieved later.

  13. def fromNanos(nanos: Long): FiniteDuration

    Construct a finite duration from the given number of nanoseconds.

    Construct a finite duration from the given number of nanoseconds. The result will have the coarsest possible time unit which can exactly express this duration.

    Exceptions thrown

    IllegalArgumentException for Long.MinValue since that would lead to inconsistent behavior afterwards (cannot be negated)

  14. def fromNanos(nanos: Double): Duration

    Construct a possibly infinite or undefined Duration from the given number of nanoseconds.

    Construct a possibly infinite or undefined Duration from the given number of nanoseconds.

    The semantics of the resulting Duration objects matches the semantics of their Double counterparts with respect to arithmetic operations.

    Exceptions thrown

    IllegalArgumentException if the length was finite but the resulting duration cannot be expressed as a FiniteDuration

  15. def unapply(d: Duration): Option[(Long, TimeUnit)]

    Extract length and time unit out of a duration, if it is finite.

  16. def unapply(s: String): Option[(Long, TimeUnit)]

    Extract length and time unit out of a string, where the format must match the description for apply(String).

    Extract length and time unit out of a string, where the format must match the description for apply(String). The extractor will not match for malformed strings or non-finite durations.

  17. implicit object DurationIsOrdered extends Ordering[Duration]

    The natural ordering of durations matches the natural ordering for Double, including non-finite values.