Packages

•  package root

  This is the documentation for the Scala standard library.

  This is the documentation for the Scala standard library.

  Package structure

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

  Notable packages include:

  • scala.collection and its sub-packages contain Scala's collections framework
    • scala.collection.immutable - Immutable, sequential data-structures such as Vector, List, Range, HashMap or HashSet
    • scala.collection.mutable - Mutable, sequential data-structures such as ArrayBuffer, StringBuilder, HashMap or HashSet
    • scala.collection.concurrent - Mutable, concurrent data-structures such as TrieMap
  • scala.concurrent - Primitives for concurrent programming such as Futures and Promises
  • scala.io - Input and output operations
  • scala.math - Basic math functions and additional numeric types like BigInt and BigDecimal
  • scala.sys - Interaction with other processes and the operating system
  • scala.util.matching - Regular expressions

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

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

  • scala.reflect - Scala's reflection API (scala-reflect.jar)
  • scala.xml - XML parsing, manipulation, and serialization (scala-xml.jar)
  • scala.collection.parallel - Parallel collections (scala-parallel-collections.jar)
  • scala.util.parsing - Parser combinators (scala-parser-combinators.jar)
  • scala.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)

  Automatic imports

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

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

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

  Definition Classes

  root

•  package scala

  Core Scala types.

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

  Definition Classes

  root

•  package 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

• Await
• Awaitable
• Batchable
• BlockContext
• CanAwait
• Channel
• DelayedLazyVal
• ExecutionContext
• ExecutionContextExecutor
• ExecutionContextExecutorService
• Future
• JavaConversions
• OnCompleteRunnable
• Promise
• SyncChannel
• SyncVar

scala.concurrent

Awaitable