Parallel collections standard library module for Scala 2.13+
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Latest commit 03abdfb May 17, 2018

Scala parallel collections

This Scala standard module contains the package scala.collection.parallel, with all of the parallel collections that used to be part of the Scala standard library.

As of Scala 2.13.0-M1, this module is a separate JAR that can be omitted from projects that do not use parallel collections.

Maintenance status

This module is maintained by the Scala team at Lightbend. If you are interested in participating, please jump right in on issues and pull requests.

Modest, targeted improvements to the existing codebase are welcome at any time. More fundamental or sweeping changes should probably wait until after the Scala 2.13 collections rework is closer to final form.


To depend on scala-parallel-collections in sbt, add this to your build.sbt:

libraryDependencies +=
  "org.scala-lang.modules" %% "scala-parallel-collections" % "0.1.2"

In your code, adding this import:

import scala.collection.parallel.CollectionConverters._

will enable use of the .par method as in earlier Scala versions.

Cross-building: dependency

This module is published only for the Scala 2.13.x series, so in a cross-built project, the dependency should take this form:

libraryDependencies ++= {
  CrossVersion.partialVersion(scalaVersion.value) match {
    case Some((2, major)) if major >= 13 =>
      Seq("org.scala-lang.modules" %% "scala-parallel-collections" % "0.1.2")
    case _ =>

This way of testing scalaVersion is robust across varying Scala version number formats (nightlies, milestones, release candidates, community build, etc).

Cross-building: source compatibility

Using .par is problematic in a cross-built project, since in Scala 2.13 the CollectionConverters._ import shown above is necessary, but in earlier Scala versions, that import will not compile.

You may able to avoid the problem by directly constructing your parallel collections rather than going through .par. For other possible workarounds, see, which is still under discussion (as of April 2017).


As with other Scala standard modules, build and release infrastructure is provided by the sbt-scala-modules sbt plugin.