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‎docs/blog/_posts/2018-04-26-eighth-dotty-milestone-release.md

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---
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layout: blog-page
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title: Announcing Dotty 0.7.0 and 0.8.0-RC1
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author: Allan Renucci
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authorImg: /images/allan.jpg
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date: 2018-04-26
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---
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Today, we are excited to release Dotty versions 0.7.0 and 0.8.0-RC1. These releases
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serve as a technology preview that demonstrates new language features and the compiler supporting them.
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If you’re not familiar with Dotty, it's a platform to try out new language concepts and compiler
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technologies for Scala. The focus is mainly on simplification. We remove extraneous syntax
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(e.g. no XML literals), and try to boil down Scala’s types into a smaller set of more fundamental
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constructs. The theory behind these constructs is researched in
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[DOT](https://infoscience.epfl.ch/record/215280), a calculus for dependent object types.
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You can learn more about Dotty on our [website](https://dotty.epfl.ch).
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<!--more-->
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This is our eighth scheduled release according to our [6-week release schedule](https://dotty.epfl.ch/docs/usage/version-numbers.html).
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The [previous technology preview](https://github.com/lampepfl/dotty/releases/tag/0.7.0-RC1) simplified
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enums, introduced erased terms, improved IDE support and improved pattern matching for GADT.
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## What’s new in the 0.8.0-RC1 technology preview?
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### sbt 1 support [#3872](https://github.com/lampepfl/dotty/pull/3872)
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Starting with Dotty 0.8.0, we will only support versions of sbt >= 1.1.4. Migrating to sbt 1
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lets us use the new improved incremental compiler for Scala called [Zinc](https://github.com/sbt/zinc),
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and enables integration with tools such as [Bloop](https://scalacenter.github.io/bloop/).
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### Unchecked warnings [#4045](https://github.com/lampepfl/dotty/pull/4045)
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Dotty now emits `unchecked` warnings like `scalac` whenever a type test is performed but cannot
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safely be checked at runtime. For example:
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```scala
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scala> def foo(x: Any) = x.isInstanceOf[List[String]]
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1 |def foo(x: Any) = x.isInstanceOf[List[String]]
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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| the type test for List[String] cannot be checked at runtime
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```
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In some cases, the Dotty compiler is smarter than `scalac` and will not emit a warning:
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```scala
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trait Marker
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def foo[T](x: T) = x match {
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case _: T with Marker => // scalac emits a spurious warning
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case _ =>
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}
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```
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### Kind Polymorphism [#4108](https://github.com/lampepfl/dotty/pull/4108)
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Normally type parameters in Scala are partitioned into kinds. First-level types are types of values.
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Higher-kinded types are type constructors such as `List` or `Map`. The kind of a type is indicated
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by the top type of which it is a subtype. Normal types are subtypes of `Any`, covariant single
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argument type constructors such as List are subtypes of `[+X] => Any`, and the `Map` type
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constructor is a subtype of `[X, +Y] => Any`.
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Sometimes we would like to have type parameters that can have more than one kind, for instance to
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define an implicit value that works for parameters of any kind. This is now possible through a form
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of (subtype) kind polymorphism. Kind polymorphism relies on the special type `scala.AnyKind` that
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can be used as an upper bound of a type.
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```scala
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def f[T <: AnyKind] = ..
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```
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The actual type arguments of f can then be types of arbitrary kinds. So the following would all be
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legal:
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```scala
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f[Int]
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f[List]
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f[Map]
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f[[X] => String]
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```
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**Note**: This feature is considered experimental and is only enabled under a compiler flag
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(i.e. `-Ykind-polymorphism`). For more information, visit the [Kind Polymorphism](https://dotty.epfl.ch/docs/reference/kind-polymorphism.html)
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section of our documentation.
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### Improved support for SAM type [#4152](https://github.com/lampepfl/dotty/pull/4152)
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This release includes fixes to SAM types that greatly improve interoperability with Java 8 lambdas.
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One can now easely write Scala code that uses Java streams:
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```scala
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val myList =
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java.util.Arrays.asList("a1", "a2", "b1", "c2", "c1")
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myList
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.stream
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.filter(s => s.startsWith("c"))
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.map(_.toUpperCase)
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.sorted
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.forEach(println(_))
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// C1
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// C2
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```
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## Trying out Dotty
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### Scastie
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[Scastie], the online Scala playground, supports Dotty.
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This is an easy way to try Dotty without installing anything.
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### sbt
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Using sbt 1.1.4 or newer, do:
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```shell
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sbt new lampepfl/dotty.g8
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```
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This will setup a new sbt project with Dotty as compiler. For more details on
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using Dotty with sbt, see the
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[example project](https://github.com/lampepfl/dotty-example-project).
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### IDE support
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It is very easy to start using the Dotty IDE in any Dotty project by following
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the [IDE guide](https://dotty.epfl.ch/docs/usage/ide-support.html).
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### Standalone installation
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Releases are available for download on the _Releases_
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section of the Dotty repository:
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[https://github.com/lampepfl/dotty/releases](https://github.com/lampepfl/dotty/releases)
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We also provide a [homebrew](https://brew.sh/) package that can be installed by running:
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```shell
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brew install lampepfl/brew/dotty
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```
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In case you have already installed Dotty via brew, you should instead update it:
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```shell
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brew upgrade dotty
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```
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## Let us know what you think!
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If you have questions or any sort of feedback, feel free to send us a message on our
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[Gitter channel](https://gitter.im/lampepfl/dotty). If you encounter a bug, please
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[open an issue on GitHub](https://github.com/lampepfl/dotty/issues/new).
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## Contributing
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Thank you to all the contributors who made this release possible!
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According to `git shortlog -sn --no-merges 0.7.0..0.8.0-RC1` these are:
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```
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TODO
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```
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If you want to get your hands dirty and contribute to Dotty, now is a good time to get involved!
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Head to our [Getting Started page for new contributors](https://dotty.epfl.ch/docs/contributing/getting-started.html),
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and have a look at some of the [good first issues](https://github.com/lampepfl/dotty/issues?q=is%3Aissue+is%3Aopen+label%3Aexp%3Anovice).
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They make perfect entry-points into hacking on the compiler.
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We are looking forward to having you join the team of contributors.
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## Library authors: Join our community build
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Dotty now has a set of widely-used community libraries that are built against every nightly Dotty
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snapshot. Currently this includes ScalaPB, algebra, scalatest, scopt and squants.
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Join our [community build](https://github.com/lampepfl/dotty-community-build)
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to make sure that our regression suite includes your library.
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[Scastie]: https://scastie.scala-lang.org/?target=dotty
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[@odersky]: https://github.com/odersky
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[@DarkDimius]: https://github.com/DarkDimius
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[@smarter]: https://github.com/smarter
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[@felixmulder]: https://github.com/felixmulder
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[@nicolasstucki]: https://github.com/nicolasstucki
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[@liufengyun]: https://github.com/liufengyun
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[@OlivierBlanvillain]: https://github.com/OlivierBlanvillain
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[@biboudis]: https://github.com/biboudis
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[@allanrenucci]: https://github.com/allanrenucci
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[@Blaisorblade]: https://github.com/Blaisorblade
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[@Duhemm]: https://github.com/Duhemm

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