Dotty 0.8.0 blog post

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

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