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@adriaanm adriaanm released this May 17, 2019 · 48 commits to 2.13.x since this release

Scala 2.13 is almost here! We are delighted to present the second 2.13 release candidate.

Since RC1, we and our crew of community contributors have been fixing bugs and improving Java interop.

We ask all library maintainers to test and publish their libraries for RC2 as soon as possible. This is crucial to validate the release candidate and enable 2.13.0 to go forward.

About these notes

These are the detailed technical release notes for RC2 only, documenting changes since RC1 only.

We don't yet have a combined, friendlier release note covering 2.13 as a whole yet. That will follow in time for 2.13.0. For now, see also the notes for RC1, M5, M4, M3, M2, and M1.

Binary compatibility

As usual for Scala pre-releases, RC2 is not binary compatible with any other Scala version, including previous 2.13 milestones and release candidates.

We will not break binary compatibility between RC2 and 2.13.0 unless really necessary.

Libraries for Scala 2.13.0-RC2

As libraries are published for RC2, they're added to .

Collections changes

To learn about the collections changes since 2.12 and how to adapt your code, take a look at these documents:

These documents are still being expanded and improved.

RC2 changes

We merged 50 pull requests for RC2. The highlights are:

  • Emit mixin forwarders as ordinary, non-bridge methods again (#8037)
  • Rework unification of Object and Any in Java/Scala interop (#7966)
  • Make Option extend IterableOnce (#8038)
  • Organize JDK converters: extension methods for Scala in scala.jdk, explicit converters for Java in jdk.javaapi (#7987)
  • Un-deprecate left Either projections (#8012)
  • Scaladoc: support setting canonical URLs (#7834)

For further changes, see merged PRs and closed bugs.

See also the notes for the previous release candidates and milestones: RC1, M5, M4, M3, M2, M1.

Compiler performance in 2.13 is 5-10% better than 2.12. The integration of the new collections library shows up in the performance graph as a nice improvement.


A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 23 contributors, according to git shortlog -sn --no-merges v2.13.0-RC1..v2.13.0-RC2. Thank you Lukas Rytz, Jason Zaugg, Aaron S. Hawley, Seth Tisue, Adriaan Moors, Stefan Zeiger, NthPortal, Michael Pollmeier, Philippus, Guillaume Martres, Diego E. Alonso-Blas, Christopher Hunt, Kenji Yoshida, Nicolas Rinaudo, Sébastien Doeraene, Arnout Engelen, Dale Wijnand, Enno Runne, Georgi Krastev, Harrison Houghton, Josh Lemer, Odd Möller, Rex Kerr.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

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