Dotty 0.9.0-RC1 Blog post

docs/blog/_posts/2018-07-06-ninth-dotty-milestone-release.md

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+---
+layout: blog-page
+title: Announcing Dotty 0.9.0-RC1
+author: Allan Renucci
+authorImg: /images/allan.jpg
+date: 2018-07-06
+---
+
+Today, we are excited to release Dotty version 0.9.0-RC1. This release serves as a technology
+preview that demonstrates new language features and the compiler supporting them.
+
+Dotty is the project name for technologies that are considered for inclusion in Scala 3. Scala has
+pioneered the fusion of object-oriented and functional programming in a typed setting. Scala 3 will
+be a big step towards realizing the full potential of these ideas. Its main objectives are to
+
+- become more opinionated by promoting programming idioms we found to work well,
+- simplify where possible,
+- eliminate inconsistencies and surprising behaviors,
+- build on strong foundations to ensure the design hangs well together,
+- consolidate language constructs to improve the language’s consistency, safety, ergonomics, and performance.
+
+You can learn more about Dotty on our [website](https://dotty.epfl.ch).
+
+<!--more-->
+
+This is our ninth 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/0.8.0-RC1) added
+support for sbt 1, introduced improved unchecked warnings and improved SAM type support.
+
+## What’s new in the 0.9.0-RC1 technology preview?
+
+### Improved REPL [#4680](https://github.com/lampepfl/dotty/pull/4680)
+The REPL now uses [JLine 3](https://github.com/jline/jline3) under the hood which improves on
+many aspects such as, auto-completions and multi-line editing. The REPL now also works on Windows!
+
+
+### Documentation support in the IDE [#4461](https://github.com/lampepfl/dotty/pull/4461), [#4648](https://github.com/lampepfl/dotty/pull/4648)
+The Dotty IDE will now display documentation while hovering over symbols that were previously
+compiled by the Dotty compiler. In the future, we plan to let users query the documentation
+in the REPL as well.
+
+
+### Drop requirement that implicit functions must be non-empty [#4549](https://github.com/lampepfl/dotty/pull/4549)
+We remove the arbitrary restriction that parameters of implicit functions must by non-empty.
+We can now write:
+```scala
+type IntProducer = implicit () => Int
+
+def prod1: IntProducer = 1
+val prod2: IntProducer = 2
+```
+
+An interesting observation is that by-name parameters can now be encoded as implicit function types:
+```scala
+def timed[T](op: => T): T = ...
+def timed[T](op: implicit () => T): T = ...
+
+timed {
+  fetch(url)
+}
+```
+
+Both definitions above are equivalent.
+
+
+### Emit feature warnings for implicit conversions [#4229](https://github.com/lampepfl/dotty/pull/4229)
+Implicit conversions are easily the most misused feature in Scala. We now emit feature warnings
+when encountering an implicit conversion definition, just like Scala 2 does.
+
+In addition, we also emit a feature warning when an implicit conversion is used,
+unless the conversion is:
+
+- an implicit class
+- co-defined with the type to which it converts
+- predefined in `scala.Predef` or is the `scala.reflect.Selectable.reflectiveSelect` conversion
+  (we might extend this to more conversions).
+
+
+### Optimise s and raw interpolators [#3961](https://github.com/lampepfl/dotty/pull/3961)
+`s` and `raw` string interpolators were known to be slower than their not type-safe counterparts:
+```scala
+s"Hello $name!"
+
+// compared to:
+"Hello " + name + "!"
+```
+The compiler will now desugar the former into the latter. Special thanks to
+[Wojtek Swiderski](https://github.com/Wojtechnology) who contributed this feature to the Dotty
+compiler!
+
+
+### Support for compiler plugins [#3438](https://github.com/lampepfl/dotty/pull/#3438)
+Dotty now supports Compiler plugins. Compiler plugins let you customize the compiler pipeline
+without having to modify the compiler source code. A major difference compared to Scala 2 is
+that Dotty plugins must run after the type checker. Being able to influence normal type checking
+is a powerful feature but for production usages, a predictable and consistent type checker is
+more important.
+
+Starting with 1.1.5 Dotty compiler plugins can be used with `sbt`. Please refer to the `sbt`
+[documentation](https://www.scala-sbt.org/1.x/docs/Compiler-Plugins.html) for more information.
+
+For more information, visit the [Compiler Plugin](http://dotty.epfl.ch/docs/reference/changed/compiler-plugins.html)
+section of our documentation.
+
+## Trying out Dotty
+
+### sbt
+Using sbt 1.1.5 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
+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
+```
+
+### Scastie
+[Scastie], the online Scala playground, supports Dotty. This is an easy way to try Dotty without
+installing anything. Note however that Scastie only supports Dotty 0.7.0-RC1.
+
+## 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 0.8.0..0.9.0-RC1` these are:
+
+```
+   200  Nicolas Stucki
+   155  Martin Odersky
+    71  Allan Renucci
+    42  Paolo G. Giarrusso
+    27  Aggelos Biboudis
+    25  Guillaume Martres
+    22  Martin Duhem
+    10  Sebastian Nadorp
+    10  Wojtek Swiderski
+     6  Olivier Blanvillain
+     5  benkobalog
+     4  Ingar Abrahamsen
+     3  Ankit Soni
+     2  Liu Fengyun
+     2  Olivier ROLAND
+     2  Fabian Page
+     1  Roberto Bonvallet
+     1  Fengyun Liu
+     1  Zoltán Elek
+     1  benkbalog
+     1  Glavo
+     1  dieutth
+     1  fschueler
+     1  mentegy
+```
+
+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