Announcing Dotty 0.24.0-RC1 - 2.13.2 standard library, better error messages and more

Hello! We are excited to announce 0.24.0-RC1 of Dotty. In this version, we have updated the standard library to 2.13.2. Also, we have made some work to make error messages more user-friendly and a bunch of other polishings to the language.

You can try out this version right now, from the comfort of your SBT, by visiting the home page and scrolling down to the "Create a Dotty Project" section.

Alternatively, you can try this version of Scala online via Scastie. Once you're there, click "Build Settings" and set "Target" to "Dotty".

Enjoy the ride🚀!

REPL works with indented code

REPL now supports indented code. Consider the following snippet:

scala> if true then
     |   print(1)
     |   print(2)

Previously, the REPL would have stopped after print(1). Now, it waits either for an else block or an extra newline to indicate the end of the expression. The above example will output 12 as expected.

Better error message for ifs that miss an else branch

The error messages are now more beginner-friendly. Consider the following:

def f: Int = if ??? then 1

Above, the if expression returns a Unit since an else clause is missing. Previously, the user would have gotten the following error:

-- [E007] Type Mismatch Error: ...
12 |def f: Int = if ??? then 1
   |             ^^^^^^^^^^^^^
   |             Found:    Unit
   |             Required: Int

Now, the above error message also contains the following sentence:

   |             Maybe you are missing an else part for the conditional?

We hope this change will make the language more intuitive for new users.

Inline overrides

Inline overrides are now supported. For example, consider the following code:

abstract class A:
  def f(x: Int) = s"Foo $x"

class B extends A:
  inline override def f(x: Int) = s"Bar $x"

@main def Test =
  val b = B()
  val a: A = b

The output of the above program is:

Bar 22
Bar 22

This new change, however, comes with rather intricated rules – if you are interested to learn about them in details, see documentation on inlines and the PR #8543 which introduced the change.

Let us know what you think!

If you have questions or any sort of feedback, feel free to send us a message on our Gitter channel. If you encounter a bug, please open an issue on GitHub.


Thank you to all the contributors who made this release possible 🎉

According to git shortlog -sn --no-merges 0.23.0-RC1..0.24.0-RC1 these are:

   136  Martin Odersky
    74  Nicolas Stucki
    37  Guillaume Martres
    33  Robert Stoll
    22  Liu Fengyun
    19  Anatolii Kmetiuk
    16  Arnaud ESTEVE
    15  Olivier Blanvillain
    10  Arnaud Esteve
     9  Martijn Hoekstra
     6  Anatolii
     4  Som Snytt
     4  bishabosha
     4  Aleksander Boruch-Gruszecki
     3  Miles Sabin
     2  odersky
     2  Fengyun Liu
     2  Julien Richard-Foy
     1  Ara Adkins
     1  Maxime Kjaer
     1  Philippus
     1  Rike-Benjamin Schuppner
     1  Julien Jean Paul Sirocchi
     1  Dani Rey
     1  Sébastien Doeraene
     1  aesteve
     1  Dale Wijnand
     1  fhackett
     1  gzoller
     1  Michael Pilquist

If you want to get your hands dirty and contribute to Dotty, now is a good time to get involved! Head to our Getting Started page for new contributors, and have a look at some of the good first issues. They make perfect entry points into hacking on the compiler.

We are looking forward to having you join the team of contributors.

Library authors: Join our community build

Dotty now has a set of widely-used community libraries that are built against every nightly Dotty snapshot. Currently, this includes shapeless, ScalaPB, algebra, scalatest, scopt and squants. Join our community build to make sure that our regression suite includes your library.

Anatolii Kmetiuk
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