We are very pleased to announce Scala 2.11.0-RC4, the next release candidate of Scala 2.11.0! Download it now from scala-lang.org or via Maven Central.
Since RC3, we’ve fixed two blocker bugs, and admitted some final polish for macros and quasiquotes. Here’s the difference between RC4 and RC3.
Please do try out this release candidate to help us find any serious regressions before the final release. The next release candidate (or the final) will be cut on Friday April 11, if there are no unresolved blocker bugs. Our goal is to have the next release be the final – please help us make sure there are no important regressions!
Code that compiled on 2.10.x without deprecation warnings should compile on 2.11.x (we do no guarantee this for experimental APIs, such as reflection). If not, please file a regression. We are working with the community to ensure availability of the core projects of the Scala 2.11.x eco-system, please see below for a list. This release is not binary compatible with the 2.10.x series, to allow us to keep improving the Scala standard library.
For production use, we recommend the latest stable release, 2.10.4.
The Scala 2.11.x series targets Java 6, with (evolving) experimental support for Java 8. In 2.11.0, Java 8 support is mostly limited to reading Java 8 bytecode and parsing Java 8 source. Stay tuned for more complete (experimental) Java 8 support.
The Scala team and contributors fixed 613 bugs that are exclusive to Scala 2.11.0-RC4! We also backported as many as possible. With the release of 2.11, 2.10 backports will be dialed back.
Since the last RC, we fixed 11 issues via 37 merged pull requests.
A big thank you to everyone who’s helped improve Scala by reporting bugs, improving our documentation, participating in mailing lists and other public fora, and – of course – submitting and reviewing pull requests! You are all awesome.
Concretely, according to git log --no-merges --oneline master --not 2.10.x --format='%aN' | sort | uniq -c | sort -rn, 111 people contributed code, tests, and/or documentation to Scala 2.11.x: Paul Phillips, Jason Zaugg, Eugene Burmako, Adriaan Moors, Den Shabalin, Simon Ochsenreither, A. P. Marki, Miguel Garcia, James Iry, Denys Shabalin, Rex Kerr, Grzegorz Kossakowski, Vladimir Nikolaev, Eugene Vigdorchik, François Garillot, Mirco Dotta, Rüdiger Klaehn, Raphael Jolly, Kenji Yoshida, Paolo Giarrusso, Antoine Gourlay, Hubert Plociniczak, Aleksandar Prokopec, Simon Schaefer, Lex Spoon, Andrew Phillips, Sébastien Doeraene, Luc Bourlier, Josh Suereth, Jean-Remi Desjardins, Vojin Jovanovic, Vlad Ureche, Viktor Klang, Valerian, Prashant Sharma, Pavel Pavlov, Michael Thorpe, Jan Niehusmann, Heejong Lee, George Leontiev, Daniel C. Sobral, Christoffer Sawicki, yllan, rjfwhite, Volkan Yazıcı, Ruslan Shevchenko, Robin Green, Olivier Blanvillain, Lukas Rytz, Iulian Dragos, Ilya Maykov, Eugene Yokota, Erik Osheim, Dan Hopkins, Chris Hodapp, Antonio Cunei, Andriy Polishchuk, Alexander Clare, 杨博, srinivasreddy, secwall, nermin, martijnhoekstra, jinfu-leng, folone, Yaroslav Klymko, Xusen Yin, Trent Ogren, Tobias Schlatter, Thomas Geier, Stuart Golodetz, Stefan Zeiger, Scott Carey, Samy Dindane, Sagie Davidovich, Runar Bjarnason, Roland Kuhn, Roberto Tyley, Robert Nix, Robert Ladstätter, Rike-Benjamin Schuppner, Rajiv, Philipp Haller, Nada Amin, Mike Morearty, Michael Bayne, Mark Harrah, Luke Cycon, Lee Mighdoll, Konstantin Fedorov, Julio Santos, Julien Richard-Foy, Juha Heljoranta, Johannes Rudolph, Jiawei Li, Jentsch, Jason Swartz, James Ward, James Roper, Havoc Pennington, Evgeny Kotelnikov, Dmitry Petrashko, Dmitry Bushev, David Hall, Daniel Darabos, Dan Rosen, Cody Allen, Carlo Dapor, Brian McKenna, Andrey Kutejko, Alden Torres.
Thank you all very much.
If you find any errors or omissions in these relates notes, please submit a PR!
Reporting Bugs / Known Issues
Please file any bugs you encounter. If you’re unsure whether something is a bug, please contact the scala-user mailing list.
Before reporting a bug, please have a look at these known issues.
Scala IDE for Eclipse
The Scala IDE with this release built in is available from this update site for Eclipse 4.2/4.3 (Juno/Kepler). Please have a look at the getting started guide for more info.
Available projects
The following Scala projects have already been released against 2.11.0-RC4! We’d love to include yours in this list as soon as it’s available – please submit a PR to update these release notes.
The following projects were released against 2.11.0-RC3, with an RC4 build hopefully following soon:
Cross-building with sbt 0.13
When cross-building between Scala versions, you often need to vary the versions of your dependencies. In particular, the new scala modules (such as scala-xml) are no longer included in scala-library, so you’ll have to add an explicit dependency on it to use Scala’s xml support.
Here’s how we recommend handling this in sbt 0.13. For the full build and Maven build, see example.
Important changes
For most cases, code that compiled under 2.10.x without deprecation warnings should not be affected. We’ve verified this by compiling a sizeable number of open source projects.
Changes to the reflection API may cause breakages, but these breakages can be easily fixed in a manner that is source-compatible with Scala 2.10.x. Follow our reflection/macro changelog for detailed instructions.
We’ve decided to fix the following more obscure deviations from specified behavior without deprecating them first.
SI-4577 Compile x match { case _ : Foo.type => } to Foo eq x, as specified. It used to be Foo == x (without warning). If that’s what you meant, write case Foo =>.
SI-7475 Improvements to access checks, aligned with the spec (see also the linked issues). Most importantly, private members are no longer inherited. Thus, this does not type check: class Foo[T] { private val bar: T = ???; new Foo[String] { bar: String } }, as the bar in bar: String refers to the bar with type T. The Foo[String]’s bar is not inherited, and thus not in scope, in the refinement. (Example from SI-8371, see also SI-8426.)
The following changes were made after a deprecation cycle (Thank you, @soc, for leading the deprecation effort!)
SI-6809 Case classes without a parameter list are no longer allowed.
SI-7618 Octal number literals no longer supported.
Finally, some notable improvements and bug fixes:
SI-7296 Case classes with > 22 parameters are now allowed.
SI-3346 Implicit arguments of implicit conversions now guide type inference.
SI-6240 Thread safety of reflection API.
#3037 Experimental support for SAM synthesis.
#2848 Name-based pattern-matching.
SI-6169 Infer bounds of Java-defined existential types.
SI-6566 Right-hand sides of type aliases are now considered invariant for variance checking.
SI-5917 Improve public AST creation facilities.
SI-8063 Expose much needed methods in public reflection/macro API.
SI-8126 Add -Xsource option (make 2.11 type checker behave like 2.10 where possible).
To catch future changes like this early, you can run the compiler under -Xfuture, which makes it behave like the next major version, where possible, to alert you to upcoming breaking changes.
Deprecations
Deprecation is essential to two of the 2.11.x series’ three themes (faster/smaller/stabler). They make the language and the libraries smaller, and thus easier to use and maintain, which ultimately improves stability. We are very proud of Scala’s first decade, which brought us to where we are, and we are actively working on minimizing the downsides of this legacy, as exemplified by 2.11.x’s focus on deprecation, modularization and infrastructure work.
The following language “warts” have been deprecated:
SI-7605 Procedure syntax (only under -Xfuture).
SI-5479 DelayedInit. We will continue support for the important extends App idiom. We won’t drop DelayedInit until there’s a replacement for important use cases. (More details and a proposed alternative.)
SI-6455 Rewrite of .withFilter to .filter: you must implement withFilter to be compatible with for-comprehensions.
SI-8035 Automatic insertion of () on missing argument lists.
SI-6675 Auto-tupling in patterns.
SI-7247 NotNull, which was never fully implemented – slated for removal in 2.12.
SI-1503 Unsound type assumption for stable identifier and literal patterns.
SI-7629 View bounds (under -Xfuture).
We’d like to emphasize the following library deprecations:
#3103, #3191, #3582 Collection classes and methods that are (very) difficult to extend safely have been slated for being marked final. Proxies and wrappers that were not adequately implemented or kept up-to-date have been deprecated, along with other minor inconsistencies.
scala-actors is now deprecated and will be removed in 2.12; please follow the steps in the Actors Migration Guide to port to Akka Actors
SI-7958 Deprecate scala.concurrent.future and scala.concurrent.promise
SI-3235 Deprecate round on Int and Long (#3581).
We are looking for maintainers to take over the following modules: scala-swing, scala-continuations. 2.12 will not include them if no new maintainer is found. We will likely keep maintaining the other modules (scala-xml, scala-parser-combinators), but help is still greatly appreciated.
Deprecation is closely linked to source and binary compatibility. We say two versions are source compatible when they compile the same programs with the same results. Deprecation requires qualifying this statement: “assuming there are no deprecation warnings”. This is what allows us to evolve the Scala platform and keep it healthy. We move slowly to guarantee smooth upgrades, but we want to keep improving as well!
Binary Compatibility
When two versions of Scala are binary compatible, it is safe to compile your project on one Scala version and link against another Scala version at run time. Safe run-time linkage (only!) means that the JVM does not throw a (subclass of) LinkageError when executing your program in the mixed scenario, assuming that none arise when compiling and running on the same version of Scala. Concretely, this means you may have external dependencies on your run-time classpath that use a different version of Scala than the one you’re compiling with, as long as they’re binary compatibile. In other words, separate compilation on different binary compatible versions does not introduce problems compared to compiling and running everything on the same version of Scala.
We check binary compatibility automatically with MiMa. We strive to maintain a similar invariant for the behavior (as opposed to just linkage) of the standard library, but this is not checked mechanically (Scala is not a proof assistant so this is out of reach for its type system).
Forwards and Back
We distinguish forwards and backwards compatibility (think of these as properties of a sequence of versions, not of an individual version). Maintaining backwards compatibility means code compiled on an older version will link with code compiled with newer ones. Forwards compatibility allows you to compile on new versions and run on older ones.
Thus, backwards compatibility precludes the removal of (non-private) methods, as older versions could call them, not knowing they would be removed, whereas forwards compatibility disallows adding new (non-private) methods, because newer programs may come to depend on them, which would prevent them from running on older versions (private methods are exempted here as well, as their definition and call sites must be in the same compilation unit).
These are strict constraints, but they have worked well for us in the Scala 2.10.x series. They didn’t stop us from fixing 372 issues in the 2.10.x series post 2.10.0. The advantages are clear, so we will maintain this policy in the 2.11.x series, and are looking (but not yet commiting!) to extend it to include major versions in the future.
Meta
Note that so far we’ve only talked about the jars generated by scalac for the standard library and reflection. Our policies do not extend to the meta-issue: ensuring binary compatibility for bytecode generated from identical sources, by different version of scalac? (The same problem exists for compiling on different JDKs.) While we strive to achieve this, it’s not something we can test in general. Notable examples where we know meta-binary compatibility is hard to achieve: specialisation and the optimizer.
In short, if binary compatibility of your library is important to you, use MiMa to verify compatibility before releasing. Compiling identical sources with different versions of the scala compiler (or on different JVM versions!) could result in binary incompatible bytecode. This is rare, and we try to avoid it, but we can’t guarantee it will never happen.
Concretely
Just like the 2.10.x series, we guarantee forwards and backwards compatibility of the "org.scala-lang" % "scala-library" % "2.11.x" and "org.scala-lang" % "scala-reflect" % "2.11.x" artifacts, except for anything under the scala.reflect.internal package, as scala-reflect is still experimental. We also strongly discourage relying on the stability of scala.concurrent.impl and scala.reflect.runtime, though we will only break compatibility for severe bugs here.
Note that we will only enforce backwards binary compatibility for the new modules (artifacts under the groupId org.scala-lang.modules). As they are opt-in, it’s less of a burden to require having the latest version on the classpath. (Without forward compatibility, the latest version of the artifact must be on the run-time classpath to avoid linkage errors.)
Finally, Scala 2.11.0 introduces scala-library-all to aggregate the modules that constitute a Scala release. Note that this means it does not provide forward binary compatibility, whereas the core scala-library artifact does. We consider the versions of the modules that "scala-library-all" % "2.11.x" depends on to be the canonical ones, that are part of the official Scala distribution. (The distribution itself is defined by the new scala-dist maven artifact.)
New features in the 2.11 series
This release contains all of the bug fixes and improvements made in the 2.10 series, as well as:
Collections
Immutable HashMaps and HashSets perform faster filters, unions, and the like, with improved structural sharing (lower memory usage or churn).
Mutable LongMap and AnyRefMap have been added to provide improved performance when keys are Long or AnyRef (performance enhancement of up to 4x or 2x respectively).
BigDecimal is more explicit about rounding and numeric representations, and better handles very large values without exhausting memory (by avoiding unnecessary conversions to BigInt).
List has improved performance on map, flatMap, and collect.
See also Deprecation above: we have slated many classes and methods to become final, to clarify which classes are not meant to be subclassed and to facilitate future maintenance and performance improvements.
Modularization
The core Scala standard library jar has shed 20% of its bytecode. The modules for xml, parsing, swing as well as the (unsupported) continuations plugin and library are available individually or via scala-library-all. Note that this artifact has weaker binary compatibility guarantees than scala-library – as explained above.
The compiler has been modularized internally, to separate the presentation compiler, scaladoc and the REPL. We hope this will make it easier to contribute. In this release, all of these modules are still packaged in scala-compiler.jar. We plan to ship them in separate JARs in 2.12.x.
Reflection, macros and quasiquotes
Please see this detailed changelog that lists all significant changes and provides advice on forward and backward compatibility.
See also this summary of the experimental side of the 2.11 development cycle.
#3321 introduced Sprinter, a new AST pretty-printing library! Very useful for tools that deal with source code.
Back-end
The GenBCode back-end (experimental in 2.11). See @magarciaepfl’s extensive documentation.
A new experimental way of compiling closures, implemented by @JamesIry. With -Ydelambdafy:method anonymous functions are compiled faster, with a smaller bytecode footprint. This works by keeping the function body as a private (static, if no this reference is needed) method of the enclosing class, and at the last moment during compilation emitting a small anonymous class that extends FunctionN and delegates to it. This sets the scene for a smooth migration to Java 8-style lambdas (not yet implemented).
Branch elimination through constant analysis #2214
Compiler Performance
Incremental compilation has been improved significantly. To try it out, upgrade to sbt 0.13.2-M2 and add incOptions := incOptions.value.withNameHashing(true) to your build! Other build tools are also supported. More info at this sbt issue – that’s where most of the work happened. More features are planned, e.g. class-based tracking.
We’ve been optimizing the batch compiler’s performance as well, and will continue to work on this during the 2.11.x cycle.
Improve performance of reflection SI-6638
IDE * Numerous bug fixes and improvements!
REPL
The bytecode decompiler command, :javap, now works with Java 7 SI-4936 and has sprouted new options SI-6894 (Thanks, @som-snytt!)
Added command :kind to help to tell ground types from type constructors. #2340 (Thanks, George Leontiev and Eugene Yokota!)
The interpreter can now be embedded as a JSR-223 Scripting Engine SI-874. (Thanks, Raphael Jolly!)
Warnings * Warn about unused private / local terms and types, and unused imports, under -Xlint. This will even tell you when a local var could be a val.
Slimming down the compiler
The experimental .NET backend has been removed from the compiler.
Scala 2.10 shipped with new implementations of the Pattern Matcher and the Bytecode Emitter. We have removed the old implementations.
Search and destroy mission for ~5000 chunks of dead code. #1648
License clarification
Scala is now distributed under the standard 3-clause BSD license. Originally, the same 3-clause BSD license was adopted, but slightly reworded over the years, and the “Scala License” was born. We’re now back to the standard formulation to avoid confusion.
A big thank you to all the contributors!
#
Author
68
Adriaan Moors
40
Iain McGinniss
9
Jason Zaugg
7
Denys Shabalin
5
Eugene Burmako
5
Simon Ochsenreither
4
A. P. Marki
1
Grzegorz Kossakowski
1
François Garillot
Commits and the issues they fixed since v2.11.0-RC3
Issue(s)
Commit
Message
SI-8466
9fbac09
SI-8466 fix quasiquote crash on recursively iterable unlifting
SI-7291, SI-8460
1c330e6
SI-8460 Fix regression in divergent implicit recovery
SI-8460
5e795fc
Refactor handling of failures in implicit search
SI-6054
91fb5c0
SI-6054 Modern eta-expansion examples that almost run
SI-5610, SI-6069
b3adae6
SI-6069 Preserve by-name during eta-expansion
SI-6054
3fb5acc
SI-6054 don't use the defunct List.map2 in example
SI-5136
71e45e0
SI-5136 correct return type for unapplySeq
SI-6195
aa6e4b3
SI-6195 stable members can only be overridden by stable members
SI-5605
1921528
SI-5605 case class equals only considers first param section
SI-6054
51f3ac1
SI-6054 correct eta-expansion in method value using placeholder syntax
SI-5155
3c0d964
SI-5155 xml patterns do not support cdata, entity refs or comments
SI-5089
84bba26
SI-5089 update definition implicit scope in terms of parts of a type
SI-7313
227e11d
SI-7313 method types of implicit and non-implicit parameter sections are never e
SI-7672
7be2a6c
SI-7672 explicit top-level import of Predef precludes implicit one
SI-5370
aa64187
SI-5370 PartialFunction is a Function with queryable domain
SI-4980
4615ec5
SI-4980 isInstanceOf does not do outer checks
SI-1972
f0b37c2
SI-1972 clarify getter and setter must be declared together
SI-5086
5135bae
SI-5086 clean up EBNF
SI-5065
32e0943
SI-5065 val/var is optional for a constructor parameter
SI-5209
64b7338
SI-5209 correct precedence of infix operators starting with ! =
SI-4249
e197cf8
SI-4249 try/catch accepts expression
SI-7937
d614228
SI-7937 In for, semi before guard never required
SI-4583
19ab789
SI-4583 UnicodeEscape does not allow multiple backslashes
SI-8388
0bac64d
SI-8388 consistently match type trees by originals
SI-8387
f10d754
SI-8387 don't match new as a function application
SI-8350
2fea950
SI-8350 treat single parens equivalently to no-parens in new
SI-8451
a0c3bbd
SI-8451 quasiquotes now handle quirks of secondary constructors
SI-8437
9326264
SI-8437 macro runtime now also picks inherited macro implementations
SI-8411
5e23a6a
SI-8411 match desugared partial functions
SI-8200
fa91b17
SI-8200 provide an identity liftable for trees
SI-7902
5f4011e
[backport] SI-7902 Fix spurious kind error due to an unitialized symbol
SI-8205
8ee165c
SI-8205 [nomaster] backport test pos.lineContent
SI-8126, SI-6566
806b6e4
Backports library changes related to SI-6566 from a419799
SI-8146, SI-8146, SI-8146, SI-8146
ff13742
[nomaster] SI-8146 Fix non-deterministic <:< for deeply nested types
SI-8420
b6a54a8
SI-8420 don't crash on unquoting of non-liftable native type
SI-8428
aa1e1d0
SI-8428 Refactor ConcatIterator
SI-8428
1fa46a5
SI-8428 Fix regression in iterator concatenation
Complete commit list!
sha
Title
2ba0453
Further tweak version of continuations plugin in scala-dist.pom
9fbac09
SI-8466 fix quasiquote crash on recursively iterable unlifting
afccae6
Refactor rankImplicits, add some more docs
d345424
Refactor: keep DivergentImplicitRecovery logic together.
1c330e6
SI-8460 Fix regression in divergent implicit recovery
5e795fc
Refactor handling of failures in implicit search
8489be1
Rebase #3665
63783f5
Disable more of the Travis spec build for PR validation
9cc0911
Minor typographical fixes for lexical syntax chapter
f40d63a
Don't mention C#
bb2a952
Reducing overlap of code and math.
3a75252
Simplify CSS, bigger monospace to match math
91fb5c0
SI-6054 Modern eta-expansion examples that almost run
b3adae6
SI-6069 Preserve by-name during eta-expansion
a89157f
Stubs for references chapter, remains TODO
0b48dc2
Number files like chapters. Consolidate toc & preface.
0f1dcc4
Minor cleanup in aisle README
6ec6990
Skip step bound to fail in Travis PR validation
12720e6
Remove scala-continuations-plugin from scala-library-all
3560ddc
Start ssh-agent
b102ffc
Disable strict host checking
0261598
Jekyll generated html in spec/ directory
71c1716
Add language to code blocks. Shorter Example title.
abd0895
Fix #6: automatic section numbering.
5997e32
#9 try to avoid double slashes in url
09f2a26
require redcarpet 3.1 for user-friendly anchors
f16ab43
use simple quotes, fix indent, escape dollar
5629529
liquid requires SSA?
128c5e8
sort pages in index
8dba297
base url
3df5773
formatting
7307a03
TODO: number headings using css
617bdf8
mathjax escape dollar
a1275c4
TODO: binding example
c61f554
fix indentation for footnotes
52898fa
allow math in code
827f5f6
redcarpet
0bc3ec9
formatting
2f3d0fd
Jekyll 2 config for redcarpet 3.1.1
e6ecfd0
That was fun: fix internal links.
d8a09e2
formatting
9c757bb
fix some links
453625e
wip: jekyllify
3fb5acc
SI-6054 don't use the defunct List.map2 in example
71e45e0
SI-5136 correct return type for unapplySeq
aa6e4b3
SI-6195 stable members can only be overridden by stable members
1921528
SI-5605 case class equals only considers first param section
51f3ac1
SI-6054 correct eta-expansion in method value using placeholder syntax
78d96ea
formatting: tables and headings
3c0d964
SI-5155 xml patterns do not support cdata, entity refs or comments
84bba26
SI-5089 update definition implicit scope in terms of parts of a type
227e11d
SI-7313 method types of implicit and non-implicit parameter sections are never e
7be2a6c
SI-7672 explicit top-level import of Predef precludes implicit one
aa64187
SI-5370 PartialFunction is a Function with queryable domain
4615ec5
SI-4980 isInstanceOf does not do outer checks
f0b37c2
SI-1972 clarify getter and setter must be declared together
5135bae
SI-5086 clean up EBNF
32e0943
SI-5065 val/var is optional for a constructor parameter
64b7338
SI-5209 correct precedence of infix operators starting with ! =
1130d10
formatting
e197cf8
SI-4249 try/catch accepts expression
622ffd4
wip
d614228
SI-7937 In for, semi before guard never required
507e58b
github markdown: tables
09c957b
github markdown: use ###### for definitions and notes
9fb8276
github markdown: use ###### for examples
19ab789
SI-4583 UnicodeEscape does not allow multiple backslashes
1ca2095
formatting
b75812d
Mention WIP in README
9031467
Catch up with latex spec.
21ca2cf
convert {\em } to _..._
37ef8a2
github markdown: numbered definition
b44c598
github markdown: code blocks
9dec37b
github markdown: drop css classes
df2f3f7
github markdown: headers
839fd6e
github markdown: numbered lists
fa4aba5
new build options
b71a2c1
updated README.md
d8f0a93
rendering error fix
ab8f966
added tex source build
a80a894
Typographical adjustments
34eb920
Fix fonts to enable both old-style and lining numerals
8f1bd7f
Over-wide line fix for types grammar
9cee383
Replaced build script with make file
3f339c8
Minor pagination tweak
50ce322
Miscellaneous cleanups:
2311e34
fix poorly labeled section links fix over-wide grammar text
e7ade69
Use the original type faces
2c21733
Adjust layout
54273a3
set Luxi Mono and Heuristica (Utopia) as the default fonts for monospace and mai
1352994
use \sigma instead of raw unicode character in math mode, as it does not render
7691d7f
added build step for ebook
9a8134a
PDF building now working with pandoc 1.10.1
ab50eec
using standard markdown for numbered lists (hopefully better rendering on github
94198c7
fixed reference to class diagram fixed undefined macro
ea177a2
fixed inline code block
cdaeb84
fixed inline code blocks fixed math array for PDF output
1ec5965
fixed inline code blocks removed LaTeX labels converted TODOs to comments
3404f54
fix for undefined macro
990d4f0
fixed undefined macros and converted comment block
580d5d6
fix for unicode character conversion error in producing PDF fix for grammar code
1847283
standard library chapter converted
7066c70
converted xml expressions and user defined annotations chapters
dc958b2
fixed minor math layout and unsupported commands
2f67c76
Converted pattern matching chapter
a327584
Implicit Parameters and Values chapter converted
a368e9c
expressions chapter converted, some math-mode errors still exist
fd283b6
conversion of classes and objects chapter
79833dc
<td style="te