Blog post on Scala 3 #872
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| by: Martin Odersky | ||
| title: "Towards Scala 3" | ||
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| Now that Scala 2.13 is around the corner, it's time to consider the | ||
| roadmap beyond it. It's been no secret that the work on Dotty over the | ||
| last 5 years was intended to explore what a new Scala could look | ||
| like. We are now at a stage where we can commit: Dotty will become | ||
| Scala 3.0. | ||
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| Of course, this statement invites many follow-up questions. Here are | ||
| some answers we can already give today. We expect there will be more | ||
| questions and answers as things shape up. | ||
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There was a problem hiding this comment. I have repeatedly encountered a persistent misconception among new and/or occasional Scala users that Dotty is somehow a new language. I suggest leading with a "How different are Scala 2 and Scala 3?" section that emphasizes continuity. Perhaps beginning with something like "Scala 2 and Scala 3 are fundamentally the same language. The compiler is new, but nearly everything Scala programmers already know about Scala 2 applies to Scala 3 as well, and most ordinary Scala 2 code will also work on Scala 3 with only minor changes." There was a problem hiding this comment. Good idea, I have added that wording. |
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| _When will it come out?_ | ||
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| The intent is to publish the final Scala 3.0 soon after Scala 2.14. At the | ||
| current release schedule (which might still change), that means late | ||
| 2019 or early 2020. | ||
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There was a problem hiding this comment. If there are no delays, we'll have 2.13 mid 2018, which means 2.14 early 2020, so "late 2019" is ambitious for 3.0 There was a problem hiding this comment. actually I was wondering about that as well, I should have said something. |
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| _What is Scala 2.14 for?_ | ||
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| Scala 2.14's main focus will be on smoothing the migration to Scala | ||
| 3. It will do this by defining migration tools, shim libraries, and | ||
| targeted deprecations, among others. | ||
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| _What's new in Scala 3?_ | ||
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| Scala has pioneered the fusion of object-oriented and functional | ||
| programming in a typed setting. Scala 3 will be a big step towards | ||
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There was a problem hiding this comment. for a general audience, better "statically typed" than just "typed", IMO. people coming from dynamic languages don't necessarily consider their languages not to be "typed". There was a problem hiding this comment. I prefer "typed". It's a matter to take back terminology to what it should mean. |
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| realizing 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, | ||
| - simplify where possible, | ||
| - eliminate inconsistencies and surprising behavior, | ||
| - build on strong foundations to ensure the design hangs well together, | ||
| - remove some language constructs that proved to be not essential, | ||
| - include some new constructs that improve the language’s consistency, safety, ergonomics, and performance. | ||
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| The main language changes, either implemented or projected, are listed | ||
| in the [Reference section on the Dotty website](http://dotty.epfl.ch/docs/reference/overview.html). | ||
| Many of the new features will be submitted to the SIP process, subject to | ||
| approval. | ||
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| _What about migration?_ | ||
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| Scala 3 is neither source nor binary compatible with Scala 2. However: | ||
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There was a problem hiding this comment. suggested wording: "As with previous Scala upgrades, Scala 3 is not binary compatible with Scala 2. They are mostly source compatible, but differences exist." simply saying "not source compatible" sounds more alarming than necessary. |
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| - Scala 3 code can link against Scala 2 artifacts (Scala 2.12 and upwards). | ||
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There was a problem hiding this comment. This is really unclear — you just said they aren't binary compatible, but now they kind of are? In fact, it sounds like Scala 3 and 2 are more binary compatible than e.g. 2.11 and 2.12 were? There was a problem hiding this comment. Yes, if this feature is mentioned, it needs to be explained; what does it do, how does it work, how is it useful? (I personlly don't understand what it is). |
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| - Scala 3 and Scala 2 share the same standard library. | ||
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There was a problem hiding this comment. perhaps "standard library sources" so it's clear they aren't the same JAR (or are they? the previous bullet leaves the reader in doubt about that) |
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| - With some small tweaks it is possible to cross-build code for both Scala 2 and 3. | ||
| We will work on a guide defining the shared language subset that can be compiled under both versions. | ||
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There was a problem hiding this comment. Instead of "We will work on", suggest the more confident "We will provide" |
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| - The Scala 3 compiler has a `-language:Scala2` option that lets it compile most Scala 2 code | ||
| and at the same time highlights necessary rewritings as migration warnings. | ||
| - The compiler can perform many of the rewritings automatically using a `-rewrite` option. | ||
| - Migration through automatic rewriting will also be offered through the `scalafix` tool, | ||
| which does not require Scala 3 to be installed. | ||
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There was a problem hiding this comment. This seems peculiar and is perhaps an unnecessary level of detail. If I'm migrating to Scala 3 anyway, why do I care if this particular step doesn't require Scala 3 to be present? |
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| _What’s the expected state of tool support?_ | ||
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| - Compiler: The Scala 3 compiler `dotc` has been used to compile itself and a growing set of libraries for a number of years now. | ||
| - IDEs: IDE support is provided by having `dotc` implement LSP, the Language Server Protocol, | ||
| including standard operations such as completion and hyperlinking and more advanced ones | ||
| such as find references or rename. There’s a VS Code plugin incorporating these operations. | ||
| Jetbrains has also released a first version of Dotty support in their Scala plugin, | ||
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There was a problem hiding this comment. consider writing "Scala 3" here instead of "Dotty" |
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| and we hope to work with them on further improvements. | ||
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| - REPL: A friendly REPL is supported by the compiler | ||
| - Docs: A revamped ScalaDoc tool generates docs for viewing in a browser and (in the future) also in the IDE.. | ||
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| - Build tools: There is a Dotty/Scala 3 plugin for sbt, and we will also work on Scala 3 integration in other build tools. | ||
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| _What about stability?_ | ||
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| - A community build contains some initial open source projects that are compiled nightly using Scala 3. | ||
| We plan to add a lot more projects to the build between now and the final release. | ||
| - We plan to use the period of developer previews to ensure that core projects are published for Scala 3. | ||
| - We have incorporated most of the Scala 2 regression tests in the Scala 3 test suite and will keep including new tests. | ||
| - In the near future we plan to build all Scala 3 tools using a previous version of the `dotc` compiler itself. | ||
| So far all tools are built first with the current Scala compiler and then again with `dotc`. | ||
| Basing the build exclusively on Scala 3 has the advantage that it lets us “eat our own dog food” | ||
| and try out the usability of Scala 3’s new language feature on a larger scale. | ||
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| _When can I try it out?_ | ||
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| You can start working with Dotty now. See the getting started | ||
| guide. Dotty releases are published every 6 weeks. We expect to have | ||
| developer previews for Scala 3.0 in the first half of 2019. | ||
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| _What about macros?_ | ||
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| Stay tuned! We are about to release another blog post specifically | ||
| about that issue. | ||
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| _How can I help?_ | ||
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| Scala 3 is developed completely in the open at | ||
| [https://github.com/lampepfl/dotty]. Get involved there, by fixing and | ||
| opening issues, making pull requests, and participating in the | ||
| discussions. | ||
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I think "around the corner" is not the right wording. There is still M4, then M5, then RC1. I would not consider 2.13 "around the corner" until RC1 is out. I think you might simply omit the whole sentence, and then in the "When will it come out?" section, insert "Scala 2.13 will come out later this year."