davoclavo / dotty-example-project

An example sbt project that compiles using Dotty

Example mill project that compiles using Dotty

NOTE: Dotty support in mill is experimental. For now, sbt remains the preferred option, see http://github.com/lampepfl/dotty-example-project for an example sbt project.

Usage

This is a normal mill project, you can compile code with mill root.compile and run it with mill root.run, mill -i root.console will start a Dotty REPL.

IDE support

Dotty comes built-in with IDE support, unfortunately this support is only available using sbt and not mill for now, see http://dotty.epfl.ch/docs/usage/ide-support.html

Using Dotty in an existing project

build.sc

Any version number that starts with 0. is automatically recognized as Dotty, you don't need to set up anything:

def scalaVersion = "0.15.0-RC1"

Nightly builds

If the latest release of Dotty is missing a bugfix or feature you need, you may wish to use a nightly build. Look at the bottom of https://repo1.maven.org/maven2/ch/epfl/lamp/dotty_0.14/ to find the version number for the latest nightly build.

Getting your project to compile with Dotty

When porting an existing project, it's a good idea to start out with the Scala 2 compatibility mode (note that this mode affects typechecking and thus may prevent some valid Dotty code from compiling) by adding to your build.sc:

def scalacOptions = T {
  if (Dep.isDotty(scalaVersion()))
    Seq("-language:Scala2")
  else
    Seq()
}

Using the Dep.isDotty method ensures that this option will only be set when compiling with Dotty.

A tool to port code from Scala 2.x to Dotty is currently in development at https://github.com/scalacenter/scalafix

If your build contains dependencies that have only been published for Scala 2.x, you may be able to get them to work on Dotty by replacing:

ivy"a::b:c"

by:

ivy"a::b:c".withDottyCompat(scalaVersion())

This will have no effect when compiling with Scala 2.x, but when compiling with Dotty this will change the cross-version to a Scala 2.x one. This works because Dotty is currently retro-compatible with Scala 2.x.

Discuss

Feel free to come chat with us on the Dotty gitter!