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‎docs/blog/_posts/2018-10-10-10th-dotty-milestone-release.md

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---
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layout: blog-page
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title: Announcing Dotty 0.10.0-RC1
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author: Allan Renucci
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authorImg: /images/allan.jpg
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date: 2018-10-10
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---
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After a long summer break, we are excited to release Dotty version 0.10.0-RC1.
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This release serves as a technology preview that demonstrates new language features and the
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compiler supporting them.
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Dotty is the project name for technologies that are considered for inclusion in Scala 3. Scala has
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pioneered the fusion of object-oriented and functional programming in a typed setting. Scala 3 will
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be a big step towards realising the full potential of these ideas. Its main objectives are to
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- become more opinionated by promoting programming idioms we found to work well,
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- simplify where possible,
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- eliminate inconsistencies and surprising behaviours,
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- build on strong foundations to ensure the design hangs well together,
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- consolidate language constructs to improve the language’s consistency, safety, ergonomics, and
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performance.
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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 10th scheduled release according to our
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[6-week release schedule](https://dotty.epfl.ch/docs/usage/version-numbers.html).
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## What’s new in the 0.10.0-RC1 technology preview?
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### Java 9+
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Dotty now supports the latest versions of Java inlcuding Java 11!
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### Type-level programming: Match Types
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We've introduced a new form of types called match types. A match types is a mechanism for checking a
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type against a pattern. A match type reduces to one of a number of right hand sides, depending on a
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scrutinee type. E.g:
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```scala
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type Elem[X] = X match {
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case String => Char
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case Array[t] => t
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case Iterable[t] => t
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}
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```
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This defines a type that, depending on the scrutinee type `X`, can reduce to one of its right hand
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sides. For instance,
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```scala
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Elem[String] =:= Char
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Elem[Array[Int]] =:= Int
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Elem[List[Float]] =:= Float
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Elem[Nil] =:= Nothing
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```
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Here `=:=` is understood to mean that left and right hand sides are mutually subtypes of each other.
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This feature is still experimental and subject to changes. For more information, visit the
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[Match Types](http://dotty.epfl.ch/docs/reference/match-types.html) section of our documentation.
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### Documentation in the REPL
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The previous release added documentation support for the IDE. Users can now query the documentation
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of sources previously compiled with Dotty within the REPL:
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```scala
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scala> /** An object */ object O { /** A def */ def foo = 0 }
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// defined object O
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scala> :doc O
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/** An object */
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scala> :doc O.foo
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/** A def */
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```
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### Tail-recursive methods can now be polymorphic
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Previously, a tail recursive call would be optimised only if the type arguments of the method
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or the enclosing class did not change at call site. E.g.
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```scala
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@tailrec def loop[T](x: T): Int = {
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...
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loop[Int](1)
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}
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```
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```shell
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loop[Int](1)
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^^^^^^^^^^^^
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Cannot rewrite recursive call: it changes type arguments on a polymorphic recursive call
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```
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This restriction has now been removed. We also improve upon `scalac` which is not able to optimise
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methods that change the type of `this` on a polymorphic recursive call.
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[Examples](https://github.com/lampepfl/dotty/blob/7a45a4a386d33180e5b7b21aa74271a77cce4707/tests/neg-tailcall/tailrec.scala#L43-L44)
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can be found in our test suite.
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### Experimental support for generic Tuples
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We augmented the `Tuple` class with generic methods such as `head`, `tail`, `apply`, `*:` and `++`.
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```scala
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scala> val t0 = (1, "2", 3L)
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val t0: (Int, String, Long) = (1,2,3)
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scala> val head = t0.head
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val head: Int = 1
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scala> val tail = t0.tail
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val tail: (String, Long) = (2,3)
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scala> val t1 = 0.0 *: t0
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val t1: (Double, Int, String, Long) = (0.0,1,2,3)
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scala> val t2 = t0 ++ t0
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val t2: (Int, String, Long, Int, String, Long) = (1,2,3,1,2,3)
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```
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### And much more!
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Please read our [release notes](https://github.com/lampepfl/dotty/releases/tag/0.10.0-RC1)
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for more details!
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## Breaking changes
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Dotty 0.10.0-RC1 requires sbt 1.2.3 and sbt-dotty 0.2.4.
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## Trying out Dotty
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### sbt
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Using sbt 1.1.5 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 the 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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### [Mill](http://www.lihaoyi.com/mill/)
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Mill version 0.2.6 introduced experimental support for Dotty. For more details on using Dotty with
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Mill, see the [example project](https://github.com/lampepfl/dotty-example-project/tree/mill).
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### IDE support
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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 0.9.0..0.10.0-RC1` these are:
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```
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219 Martin Odersky
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142 Nicolas Stucki
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67 Paolo G. Giarrusso
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52 Allan Renucci
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48 Guillaume Martres
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39 Martin Duhem
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23 Liu Fengyun
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15 Olivier Blanvillain
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10 Dmytro Melnychenko
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10 Abel Nieto
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10 Sébastien Doeraene
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7 Jaemin Hong
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7 Eugene Melekhov
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5 Saloni Vithalani
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3 Daniel Li
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3 Dale Wijnand
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3 Jasper Moeys
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2 lloydmeta
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2 Aggelos Biboudis
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2 Greg Pevnev
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1 Adriaan Moors
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1 Lukas Rytz
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1 Kazuhiro Sera
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1 Justin du Coeur, AKA Mark Waks
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1 Jan Rock
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1 Fengyun Liu
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1 Szymon Pajzert
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1 Chris Birchall
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1 benkobalog
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1 Martijn Hoekstra
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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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