Scala 2.10.0 (english version)

Where did we came from, and where are we going to? Daniel Capó Sobral Last revision: Jan 05, 2013

Revision History Jul 20, 2012: add IsSeqLike and Searching Aug 08, 2012: removed previous revision – it didn’t make 2.10.0; added raw interpolator; added :warnings; renamed makro to macros; @static; scaladoc grouping and link to anything Aug 09, 2012: fixed stuff on macros and reflect; fixed stuff with Try; added references to other presentations Sep 20, 2012: rescue replaced with recoverWith Jan 05, 2014: Incorporate feedback about macros; improve actors; add links to some docs;

Who am I? Daniel C. Sobral @ Stack Overflow dcsobral @ Twitter, Gmail/Gtalk, Skype, SliderShare Daniel Sobral @ Facebook, Speaker Deck, LinkedIn http://www.linkedin.com/in/danielsobral http://www.slideshare.net/dcsobral https://speakerdeck.com/u/dcsobral http://dcsobral.blogspot.com

What do I know about Scala? Scala gold badge @ Stack Overflow Small contributions to Scala:  code optimization  enhancements  bug fixes  documentation (not that small) Active member of the Scala community (mailing lists, irc) Blog about Scala

IMPORTANT! Scala 2.10.0 has not been released!  At the time this presentation has been written... (July, 07, 2012) The information that follows may be changed before 2.10.0 is released.

Summary History Near Future  Versioning  Release Process  Bug fixes  Enhancements  SIPs (Scala Improvement Process)  Reflection  Actors and Akka Distant Future

Release History 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 • 0.8.1 • 1.0.0 • 1.4.0 • 2.0.0 • 2.3.2 • 2.7.1 • 2.7.3 • 2.8.0 • 2.9.0 • 2.9.2 • 0.8.2 • 1.1.0 • 2.1.0 • 2.3.3 • 2.7.2 • 2.7.4 • 2.8.1 • 2.9.1 • 0.9.0 • 1.1.0 • 2.1.1 • 2.4.0 • 2.7.5 • 2.8.2 • 0.9.1 • 1.1.1 • 2.1.2 • 2.5.0 • 2.7.6 • 1.2.0 • 2.1.3 • 2.5.1 • 2.7.7 • 1.3.0 • 2.1.5 • 2.6.0 • 2.1.6 • 2.6.1 • 2.1.7 • 2.1.8 • 2.2.0 • 2.3.0 • 2.3.1

Some important landmarks 2011 • Parallel Collections 2010 • New Collections Design • Binary Compatibility of Minor Releases 2008 • Java Generics • Case Class Extractors 2007 • Extractors • Private/protected primary constructors • Private[this] • Placeholder 2006 parameters • Scalac written in • Early Initialization Scala • Abstract Type • Implicits Constructors • Traits e • Existential Types linearization • Lazy values • Structural Types Not comprehensive, by any means! • Multilline Strings

Explaining Versioning 2 .9 .1 -1 Bug Epoch Major Minor fix

Versioning – Scala 2.10.0 Major release Binary incompatible with previous versions Language changes Library changes New deprecations Removal of deprecated features  Classes  Methods  Language syntax

Examples of New Deprecations Octal numbers! scala> 077 <console>:1: warning: Treating numbers with a leading zero as octal is deprecated. 077 ^ res10: Int = 63 Double ending in dot scala> 1. <console>:1: warning: This lexical syntax is deprecated. From scala 2.11, a dot will only be considered part of a number if it is immediately followed by a digit. 1. ^ res11: Double = 1.0

Examples of removal of deprecatedfeatures Language syntax for ( val i <- 1 to 10) println(i) Class scala.collection.mutable.CloneableCollection Method scala.collection.immutable.Queue.+ Package scala.testing.SUnit

Improvements of the releaseprocess Process becoming more and more automated Package for RPM, APT, Brew, etc  Automatically generated! Milestones used to help integrate libraries and frameworks  M4 June 12  M5 soon! Release Candidates to consolidate and fix bugs

Bug fixes Many fixes! New pattern matcher! Ticket priorization! New warnings:  Detecting bugs in the compiler itself! More third party contributions!  git + pull request == FTW ...besides the natural improvements of the codebase.

Closed Tickets 102 451 490 622 896 963 1118 1133 1195 1201 1247 13361430 1431 1432 1439 1510 1785 1799 2089 2094 2171 2196 23082322 2337 2388 2405 2435 2442 2460 2764 2782 2807 3047 30483098 3240 3272 3326 3343 3371 3392 3481 3566 3569 3628 37023708 3718 3755 3758 3761 3770 3798 3853 3854 3880 3898 39293960 3999 4018 4019 4025 4027 4063 4070 4098 4110 4124 41344147 4171 4172 4176 4216 4262 4270 4271 4273 4319 4326 43364355 4372 4391 4398 4417 4419 4425 4430 4441 4461 4467 44694478 4482 4490 4494 4501 4510 4512 4515 4535 4540 4541 45424547 4553 4561 4568 4570 4573 4574 4578 4579 4584 4592 45934595 4599 4601 4627 4636 4642 4647 4651 4656 4658 4661 46924696 4697 4709 4712 4713 4716 4717 4723 4727 4731 4737 47404749 4753 4757 4758 4759 4761 4764 4766 4770 4777 4780 4792

Closed Tickets4794 4800 4802 4804 4807 4809 4811 4818 4823 4827 4828 48314833 4839 4842 4846 4851 4853 4857 4858 4859 4860 4861 48694871 4874 4875 4877 4879 4882 4891 4894 4898 4899 4909 4910 4911 4925 4928 4929 4933 4935 4938 4954 4957 4959 4961 49634970 4975 4976 4979 4981 4985 4987 4989 5005 5009 5012 50185020 5023 5026 5029 5032 5033 5034 5037 5040 5041 5053 50545056 5062 5063 5066 5071 5072 5077 5078 5080 5083 5084 50855093 5096 5097 5099 5104 5105 5108 5117 5119 5121 5125 5127 5135 5137 5147 5148 5152 5156 5162 5165 5167 5168 5175 5176 5178 5189 5199 5201 5205 5206 5210 5212 5215 5223 5226 52295230 5239 5245 5248 5256 5259 5266 5267 5272 5284 5287 52915293 5295 5300 5305 5313 5317 5318 5328 5334 5336 5341 53435344 5352 5354 5356 5358 5359 5373 5374 5375 5377 5382 5384

Closed Tickets (442 – July 2nd)5387 5399 5405 5406 5407 5426 5428 5429 5441 5444 5446 54515452 5453 5455 5471 5488 5489 5497 5500 5510 5514 5522 55285530 5532 5535 5537 5542 5543 5544 5545 5552 5553 5554 5564 5571 5572 5577 5578 5580 5589 5590 5591 5593 5599 5608 56095610 5612 5614 5617 5623 5626 5627 5629 5632 5640 5641 56445648 5652 5654 5655 5656 5663 5666 5667 5672 5676 5677 56805682 5683 5688 5689 5690 5693 5696 5702 5703 5704 5706 57075708 5713 5715 5720 5728 5729 5735 5738 5742 5760 5761 57635769 5777 5779 5796 5801 5804 5805 5809 5816 5821 5829 58395840 5843 5845 5846 5853 5857 5862 5867 5879 5880 5881 58995910 5912 5914 5932 5953 5966 5967 5968 5971 5986 etc?

Enhancements New collections  Mutable SortedSet/SortedMap (AVL-based)  Mutable Concurrent Map (TrieMap)  Parallel Mutable Concurrent Map (ParTrieMap) Performance:  Immutable SortedSet/SortedMap  New (private) RedBlackTree  TreeIterator  PartialFunction  applyOrElse  BitSet  MurmurHash3 (collections, xml, case classes)

New stuff Type Classes:  Hashing (there’s an Equiv already)  IsTraversableOnce and IsTraversableLike Try (Twitter’s alternative to Either) Package scala.util.hashing Configurable Pools for parallel collections @static @unspecialized to[Collection] ???

New compile parameters override object (-Yoverride-objects) bytecode version 49, 50 and 51 (-target:jvm-1.x-asm) -optimize faster and more effective (ok, not new) -Dscala.timings=true shows what’s is taking so long to compile SIP-18: -language:XXX, -feature various logs various macro various patmat etc

New REPL commands The :warnings command will turn on all hidden warnings, such as deprecation (that one is going to my finger’s muscle memory...)

scala.util.hashing.Hashing def hashingOf[T : Hashing](obj: T): Int = implicitly[Hashing[T]].hash(obj) // A bad hashing function for Seqs implicit val seqHashing = Hashing fromFunction ((_: Seq[_]).size)

IsTraversableOnce andIsTraversableLike class FilterMapImpl[A, Repr] (val r: GenTraversableLike[A, Repr]) { final def filterMap[B, That] (f: A => Option[B]) (implicit cbf: CanBuildFrom[Repr, B, That]) : That = r.flatMap(f(_).toSeq) } // How to write the implicit conversion???

IsTraversableOnce andIsTraversableLike Obstacles to writing the implicit conversion:  Array and String are not GenTraversable  String does not have a type parameter (A)  Nor BitSet and other collections  Inference over view bounds is difficult IsTraversableOnce and IsTraversableLike provides a solution

IsTraversableOnce andIsTraversableLike class FilterMapImpl[A, Repr] (val r: GenTraversableLike[A, Repr]) { final def filterMap[B, That] (f: A => Option[B]) (implicit cbf: CanBuildFrom[Repr, B, That]) : That = r.flatMap(f(_).toSeq) } implicit def filterMap[Repr, A](r: Repr) (implicit fr: IsTraversableOnce[Repr]) : FilterMapImpl[fr.A,Repr] = new FilterMapImpl(fr.conversion(r))

scala.util.Try def percentCompleted(total: Int, done: Int): Int = Try ( done * 100 / total ) getOrElse 100

scala.util.Try Try { new FileInputStream(a) } recoverWith { case _: FileNotFoundException => Try(new FileInputStream(b)) } recover { case _: FileNotFoundException => defaultInputStream } andThen { stream => in = stream.read(); stream.close(); in }

@static Turn object fields into static fields of the object’s companion class Fields are initialized through the static initializer of the class Access to these fields are turned into direct static field access

Configurable Pools on ParallelCollectionsimport scala.collection.parallel._val pc = mutable.ParArray(1, 2, 3)pc.tasksupport = new ForkJoinTaskSupport( new scala.concurrent.ForkJoinPool(2))pc map { _ + 1)pc.tasksupport = new ThreadPoolTaskSupport()

Configurable Pools on ParallelCollections – Customizingclass customTaskSupport extends TaskSupport { def execute[R, Tp] (task: Task[R, Tp]): () => R = ??? def executeAndWaitResult[R, Tp] (task: Task[R, Tp]): R = ??? def parallelismLevel: Int = ???}

to[Collection]scala> List(2, 1, 3).to[Seq]res17: Seq[Int] = Vector(2, 1, 3)scala> List(2, 1, 3).to[Vector]res18: Vector[Int] = Vector(2, 1, 3)scala> List(2, 1, 3).to[collection.mutable.Seq]res19: scala.collection.mutable.Seq[Int] = ArrayBuffer(2,1, 3)scala> List(2, 1, 3).to[collection.immutable.SortedSet]res20: scala.collection.immutable.SortedSet[Int] =TreeSet(1, 2, 3)

??? ??? it‘s a Nothing-returning that throws exceptions Because it’s type is Nothing, ??? may replace any expression Excellent for stubs, exercises and presentations!

???trait Opt [A] { // Exercise by Tony Morris def fold[X](some: A => X, none: => X): X = ??? def map[B](f: A => B): Opt[B] = ??? def get: A = ??? def flatMap[B](f: A => Opt[B]): Opt[B] = ??? def mapAgain[B](f: A => B): Opt[B] = ??? def getOrElse(e: => A): A = ??? def filter(p: A => Boolean): Optional[A] = ??? def exists(p: A => Boolean): Boolean = ??? def forall(p: A => Boolean): Boolean = ??? def foreach(f: A => Unit): Unit = ??? def isDefined: Boolean = ??? def orElse(o: => Opt[A]): Opt[A] = ??? // etc Adapted from Tony Morris, http://blog.tmorris.net/further-understanding-scalaoption/

Enhancements Scaladoc  Implicits!  Diagrams!  Link to anything!  Group things! API docs  Steady stream of improvements on the documents themselves See also:  http://docs.scala-lang.org/

ScalaDoc & Implicits scaladoc -implicits

Class Diagrams! scaladoc -diagrams

Parallel Collections Docs! Available at http://docs.scala-lang.org/

Scaladoc – Link to anything! [[x.y.Z.m]] links to m on Z, defaulting to the type Z if m is present on both type and object Z! forces type and Z$ forces object, to disambiguate m can be written with type signature, to disambiguate [[m]] refers to m on the current scope If dots or hashes are required in the type signature, escape them with

Scaladoc – Group things! Scaladoc now has attributes that allow members to be grouped, and the groups described and prioritized Members of the same group are displayed together Groups of lower priority are seen before groups of higher priorities See: @group, @groupdesc, @groupname and @groupprio

SIP – Scala Improvement Process SIP-11: String Interpolation SIP-12: Uncluttering Scala’s syntax for control structures SIP-13: Implicit Classes SIP-14: Futures and Promises SIP-15: Value Classes SIP-16: Self-cleaning Macros SIP-17: Type Dynamic SIP-18: Modularizing Language Features SIP-19: Implicit Source Locations

SIP – Scala Improvement Process SIP-11: String Interpolation (accepted!) SIP-12: Uncluttering Scala’s syntax for control structures (postponed) SIP-13: Implicit Classes (accepted!) SIP-14: Futures and Promises (accepted!) SIP-15: Value Classes (accepted!) SIP-16: Self-cleaning Macros (postponed) SIP-17: Type Dynamic (accepted!) SIP-18: Modularizing Language Features (accepted!) SIP-19: Implicit Source Locations (not accepted)

SIP-11: String Interpolation Lack of string interpolation were a source of constant complains  Even though very few languages support them! Odersky says the difference between ${x} and "+x+" is a single character  If you ignore the shift-typing...  Someone says " and + can be typed without shift on a swiss keyboard  True! About-face:  What if string interpolation was more than string interpolation?

SIP-11: String Interpolationdef hello(name: String = "world"): String = "Hello, " + name + "! "// Interpolation!def hello(name: String = "world"): String = s"Hello, $name! "

SIP-11: String Interpolationdef percentCompleted(total: Int, done: Int): String = Try ( done * 100 / total ) map { percent => f"$percent%2d% completed" } getOrElse "100% completed"def percentCompleted(total: Int, done: Int): String = Try ( f"${ done * 100 / total }%2d% completed" ) getOrElse "100% completed"

SIP-11: String Interpolation:How does it work?s"Hello, $name!" // becomesStringContext("Hello, ", "!").s(name)f"${ done * 100 / total }%2d% completed" // becomesStringContext("", "%2d% completed").f(done * 100 / total)raw"String with n in it"

SIP-11: String Interpolation Multiline literals work too  s"""Ok!""" Interpolation may be nested  s"${ s"$x" }" Backslash is not used as escape character  r"d+/$month" // not an actual interpolator!  StringContext("""d+/""").r(month) But both s and f interpolators add the escaping themselves!  s"Hello, $name!n" // newline normal But the raw interpolator does not! How to add/modify behavior:  Enrich My Library on StringContext  Shadowing of object StringContext  Added interpolators don’t actually need to be methods!

SIP-11: String Interpolation// Enrich My Libraryclass RegexContext(sc: StringContext) { def r(args: Any*) = { sc.checkLengths(args: _*) val res = (args, sc.parts.tail).zipped map { (arg, part) => s"Q$argE$part" } mkString "" (sc.parts.head + res).r }}implicit def toRC(sc: StringContext) = new RegexContext(sc)

SIP-11: String Interpolation// Interpolation nestingclass RegexContext(sc: StringContext) { def r(args: Any*) = { sc.checkLengths(args: _*) s"${sc.parts.head}${ (args, sc.parts.tail).zipped map { (arg, part) => s"Q$argE$part" } mkString "" }".r }}implicit def toRC(sc: StringContext) = new RegexContext(sc)

SIP-11: String Interpolation// Shadowing of StringContext objectobject StringContext(parts: String*) { def r(args: Any*) = { require(parts.length == args.length + 1) val res = (args, parts.tail).zipped map { "Q" + _ + "E" + _ } mkString "" (parts.head + res).r }}// One can change s and f interpolators!

SIP-11: String Interpolation// apply and unapplySeqdef hello(name: String = "world"): String = i"Hello, $name!"def who(message: String): String = message match { case i"Hello, $name!" => name case _ => “no clue"}who(hello("Daniel")) == "Daniel"

SIP-11: String Interpolation// apply and unapplySeqimplicit class SI(sc: StringContext) { object i { def apply(args: Any*): String = sc.parts.head + (args,sc.parts.tail).zipped.map(_+_).mkString def unapplySeq(s: String): Option[Seq[String]] = { val partsr = sc.parts map (p => s"Q$pE") val r = (partsr mkString "(.*)").r s match { case r(xs @ _*) => Some(xs) case _ => None } } }}

SIP-13: Implicit Classes “Enrich My Library” (formely “Pimp My Library”) very popular But with lots of cerimony... “Extension methods” becoming common in other languages (even Java!) And with less cerimony at that! Solution: implicit class

SIP-13: Implicit Classes// String interpolation with Implicit Classesimplicit class RegexContext(sc: StringContext) { def r(args: Any*) = { sc.checkLengths(args: _*) val res = (args, sc.parts.tail).zipped map { "Q" + _ + "E" + _ } mkString "" (sc.parts.head + res).r }}

SIP-14: Futures and Promises Non-blocking asynchronous of operations is a common task Evidence: many libraries have a Future implementation  Including Scala Actors library! Problem:  Non-standard interface  Interface tied to implementation Solution:  Powerful and flexible API implementing the concepts of Future and Promise

SIP-14: Futures and Promises// TODO – Sorry! Examples from SIP:import scala.concurrent._val f: Future[List[String]] = future { session.getRecentPosts}f onComplete { case Right(posts) => for (post <- posts) render(post) case Left(t) => render("An error has occured: " +t.getMessage)}

SIP-14: Futures and Promises// TODO – Sorry! Examples from SIP:import scala.concurrent._val f: Future[List[String]] = future { session.getRecentPosts}f onFailure { case t => render("An error has occured: " + t.getMessage)} onSuccess { case posts => for (post <- posts) render(post)}

SIP-14: Futures and Promises// TODO – Sorry! Examples from SIP:import scala.concurrent._def main(args: Array[String]) { val rateQuote = future { connection.getCurrentValue(USD) } val purchase = rateQuote map { quote => if (isProfitable(quote)) connection.buy(amount,quote) else throw new Exception("not profitable") } blocking(purchase, 0 ns)}

SIP-14: Futures and Promises// TODO – Sorry! Examples from SIP:import scala.concurrent.{ future, promise }val p = promise[T]val f = p.futureval producer = future { val r = produceSomething() p success r continueDoingSomethingUnrelated()}val consumer = future { startDoingSomething() f onSuccess { case r => doSomethingWithResult() }}

SIP-15: Value Classes Curse of references Curse of boxing:  case class Meter(n: Int) much more “expensive” than int Curse of implicit classes:  "abc“.r creates an unnecessary object just to call new Regex("abc") We want a class that is not a reference! Solution: value classes.

SIP-15: Value Classes// String interpolation with implicit value class!implicit class RegexContext(sc: StringContext) extends AnyVal { def r(args: Any*) = { sc.checkLengths(args: _*) val res = (args, sc.parts.tail).zipped map { "Q" + _ + "E" + _ } mkString "" (sc.parts.head + res).r }}

SIP-15: Value Classes Can have only one parameter  Which must be a public val For instance, [T: Ordering](v: T) is not acceptable Can be extended by traits  If they are either Any or AnyVal Cannot define equality or hash code  But may be case classes! Equality and hash code are applied over the parameter They are effectively “final” On a local scope, the class is optimized away! If they escape scope, they are boxed

SIP-16: Macros Acceptance postponed, but available experimentally on Scala 2.10.0 Large compilers are hard to maintain  Pressure against new features on the compiler Compiler Plugins can be used to extend Scala...  ...but they are difficult to keep in sync with scalac Possible solution: Macros  “Macros? Ugh!” –C/C++ trauma! Something new: scala.reflection  Macros become almost free!

SIP-16: Macros Scala CATs!  Compile-time AST Transformations  Abstract Syntax Tree Inspired by Nemerle macros Four kind looked into:  Typed def macros – This is the only made available!  Untyped def macros  Type (class/trait) macros  Annotation macros Official Overview:  http://docs.scala-lang.org/overviews/macros/typemacros.html

SIP-16: Macros// Typed def macros(1 to 5).foreach(println) ^ ^ | + Type check + Macro execution + New type check

SIP-16: Macros// Untyped def macrosfor {val i = 0; i < 10; i += 1} println(i)^ ^| || + Arguments not type checked!+ Macro execution+ Type check

SIP-16: Macros// Untyped def macros – why?for {val i = 0; i < 10; i += 1} println(i) ^ ^ | “i” not visible in this scope! + + “i” only visible in this scope.

SIP-16: Macros// Type (class/trait) macrosclass User extends DbTable(jdbcUrl, “t_user”) ^ + Macro// Connects to database at compile time// and gets table description to create// class “User”

SIP-16: Macros Type macros are similar to F#’s type providers Next in line of development First user likely to be Typesafe’s Slick (formely ScalaQuery)  http://slick.typesafe.com/

SIP-16: Macros// Macro annotations@memoizedef fat(n: Int) = if (n > 0) n * fat(n – 1) else 1// Macro applied over the annotated definition,// be it class, method, parameter, etc

SIP-16: Macros Only typed macros made available... And with experimental status, at that... Behind flag –language:experimental.macros... But already used in some places on the library! C/C++ macros trauma very widespread... ...but the true C++ macros are templates! (imho) Macro Paradise used to experiment with other types of macros:  http://docs.scala-lang.org/overviews/macros/paradise.html

SIP-16: Macros Typed Macros Advantages:  Relatively simple to implement  There’s no difference in the type signature of a method implemented with a macro!  Easy to test  Hygienic macros provided through a macro!  Therefore, self-cleaning  Non-hygienic Macros are also easy to create

SIP-16: Macros Disadvantages:  Somewhat limited  Two-stages compilation  It’s not possible to define and use a macro on the same compilation  Non-hygienic by default  Nay-sayers will go on nay-saying.

SIP-16: Macrosobject Trimmer { def trim(s: String): String = macro trimImpl import scala.reflect.macros.Context def trimImpl(c: Context)(s: c.Expr[String]): c.Expr[String] = { import c.universe._ // see reflection val Literal(Constant(untrimmed: String)) = s.tree val trimmed = untrimmed.lines.map(_.trim).mkString("n") c.Expr(Literal(Constant(trimmed))) }}

SIP-16: Macros Path dependent method types:  def m(c: Context)(param: c.Expr[Any]): c.Expr[Any] Through –Ydependent-method-types parameter on previous versions Reflection, reflection and reflection!  “Once we do reflection right, we get macros for free!” – paraphrasing Martin Odersky

SIP-17: Type Dynamic Problems:  Scala’s integration to other JVM languages assumes static typing  Lots of dynamically typed languages on the JVM!  Static typing also hinders some flexible DSLs Solution: trait Dynamic Similar to “missing method” Makes it easy to integrate with other JVM languages Has great DSL potential And other uses as well...

SIP-17: Type Dynamicscala> class xmlPath(xml: scala.xml.Node) extends Dynamic { | def selectDynamic(path: String) = xml path | }defined class xmlPathscala> new xmlPath(<root><a><b><c/></b></a></root>).bres9: scala.xml.NodeSeq = NodeSeq(<b><c/></b>)

SIP-17: Type Dynamic Method call conversions: Standard methods:  applyDynamic Methods with named parameters:  applyDynamicNamed Setters:  updateDynamic Getters (nullary methods):  selectDynamic

SIP-17: Type Dynamic Also in the works is DynamicProxy  Add/Change methods, have everything else be automatically redirected  Might (maybe) even do so with static typing, through macros! However, not yet in the library  Might make 2.10.0 or not – time will tell

SIP-18: Modularizing LanguageFeatures Problems:  Some Scala features are hard to understand  Others induce errors  And some are experimental But they are all necessary, for one reason or another! Solution: SIP-18

SIP-18: Modularizing LanguageFeatures Controls access to some language features Using these features cause compilation warnings  Which might become compilation errors in the future Access to features allowed through:  compile flags  implicit in scope Access can be allowed through inherited ScalaDoc explains why control and why make available

SIP-18: Modularizing LanguageFeatures Contentious features:  Postfixed operators  Method invocation made using implicit reflection  Implicit conversions  Higher kinded types  Existentials  Except for those equivalent to Java wildcard types  Type Dynamic Experimental Features  Macros

SIP-18: Modularizing LanguageFeatures// Postfix operatorscala> "abc" lengthwarning: there were 1 feature warnings; re-run with -feature fordetailsres0: Int = 3

SIP-18: Modularizing LanguageFeatures// Postfix operator, using -featurescala> "abc" length<console>:8: warning: postfix operator length should be enabledby making the implicit value language.postfixOps visible.This can be achieved by adding the import clause importlanguage.postfixOpsor by setting the compiler option -language:postfixOps.See the Scala docs for value scala.language.postfixOps for adiscussionwhy the feature should be explicitly enabled. "abc" length ^res0: Int = 3

SIP-18: Modularizing LanguageFeatures// Methods called using reflectionscala> val x = new AnyRef { def hello = println("world") }x: Object{def hello: Unit} = $anon$1@7d628303scala> x.hello<console>:10: warning: reflective access of structural type member method helloshould be enabledby making the implicit value language.reflectiveCalls visible.This can be achieved by adding the import clause import language.reflectiveCallsor by setting the compiler option -language:reflectiveCalls.See the Scala docs for value scala.language.reflectiveCalls for a discussionwhy the feature should be explicitly enabled. x.hello ^world

SIP-18: Modularizing LanguageFeatures// Implicit conversionsscala> implicit def f(s: String): Int = Predef.augmentString(s).toInt<console>:8: warning: implicit conversion method f should be enabledby making the implicit value language.implicitConversions visible.This can be achieved by adding the import clause importlanguage.implicitConversionsor by setting the compiler option -language:implicitConversions.See the Scala docs for value scala.language.implicitConversions for adiscussionwhy the feature should be explicitly enabled. implicit def f(s: String): Int = Predef.augmentString(s).toInt ^f: (s: String)Int

SIP-18: Modularizing LanguageFeatures The feature being limited are implicit conversions Other implicit usages are still allowed Implicit conversions through implicit classes works too

SIP-18: Modularizing LanguageFeatures// Higher Kinded Typesscala> class Monad[M[_]]<console>:9: warning: higher-kinded type should be enabledby making the implicit value language.higherKinds visible.This can be achieved by adding the import clause importlanguage.higherKindsor by setting the compiler option -language:higherKinds.See the Scala docs for value scala.language.higherKinds for adiscussionwhy the feature should be explicitly enabled. class Monad[M[_]] ^defined class Monad

SIP-18: Modularizing LanguageFeatures// Existentialsscala> val l: List[ T forSome { type T }] = List(1)<console>:7: warning: the existential type T forSome { type T },which cannot be expressed by wildcards, should be enabledby making the implicit value language.existentials visible.This can be achieved by adding the import clause importlanguage.existentialsor by setting the compiler option -language:existentials.See the Scala docs for value scala.language.existentials for adiscussionwhy the feature should be explicitly enabled. val l: List[ T forSome { type T }] = List(1) ^l: List[T forSome { type T }] = List(1)

SIP-18: Modularizing LanguageFeatures// Type DynamicTODO

SIP-18: Modularizing LanguageFeatures// Macrosscala> def g(d: Any): Any = macro f<console>:12: error: macro definition needs to be enabledby making the implicit value language.experimental.macrosvisible.This can be achieved by adding the import clause importlanguage.experimental.macrosor by setting the compiler option -language:experimental.macros.See the Scala docs for value scala.language.experimental.macrosfor a discussionwhy the feature needs to be explicitly enabled. def g(d: Any): Any = macro f ^

scala.reflect Allows us to explore the structure of a program, and interact with that structure  Wikipedia: reflection happens at compile time  Scala: you use the same API at compile time as well, with macros Main Concepts:  Reflection Libraries and Universes  Names, symbols, types and trees  Mirrors Overview will be provided at:  http://docs.scala-lang.org/overviews/reflection/overview.html

scala.reflect – Universes Source: Scala Reflection Pre-SIPNotice: all of the classes on scala-library.jar depicted above were removed.

scala.reflect – Universes Contains a number of interrelated elements which, together, make up the main components of reflection  Symbol  Tree  Name  etc... Use of path dependent types to relate types with the universes they came from

scala.reflect – Universes Built in layers with different degrees of detail using the “cake pattern” :  Base:  Fundamental concepts  Identity, e and little else  JavaUniverse  Manipulation through JVM-provided reflection, enhanced with information provided by Scala  Macros  Manipulation at compile time  Compiler’s universe, but presented with a more restricted API  Others: compiler

scala.reflect – Main Types Name FlagSet Symbol Universe AnnotationInfo Type Position Tree

scala.reflect – Name Name TermName TypeName

scala.reflect – Name Scala has two namespaces:  Types  Values (Term) Name ties a string to one of those namespaces Name also enables convertion of names from language- representation to class-file representation

scala.reflect – Symbol Symbol Type owner Name Symbol Type ... Symbol TermName TypeName

scala.reflect – Symbol All definitions are tied to symbols  Classes  Methods  Parameters  Variables  If you named it, it has a symbol  If you did not name it, but refer to it as being “anonymous”, it also has a symbol Immutable at run time  At macro time, one can change its flags

scala.reflect – Type Structure associated with a symbol:  Class members  Parameters and return types of a method  etc Made up of case classes Handled through pattern matching

scala.reflect – Types and Symbolsscala> import scala.reflect.runtime.universe._import scala.reflect.runtime.universe._scala> typeOf[List[Int]]res0: reflect.runtime.universe.Type = List[Int]scala> res0.member(newTermName("head"))res1: reflect.runtime.universe.Symbol = method headscala> res1.typeSignatureres2: reflect.runtime.universe.Type = => Ascala> res1.typeSignatureIn(res0)res3: reflect.runtime.universe.Type = => Int

scala.reflect – Types and Symbolsdef intMethods[T : TypeTag](v: T) = { val IntType = typeOf[Int] val vType = typeOf[T] val methods = vType.members.collect { case m: MethodSymbol if m.isPublic => m -> m.typeSignatureIn(vType) } methods collect { // Pattern-matching various method types: case (m, mt @ NullaryMethodType(IntType)) => m -> mt case (m, mt @ MethodType(_, IntType)) => m -> mt case (m, mt @ PolyType(_, MethodType(_, IntType))) => m -> mt }}

scala.reflect – Types and Symbolsdef intMethods[T : TypeTag](v: T) = { val IntType = typeOf[Int] val vType = typeOf[T] val methods = vType.members.collect { case m: MethodSymbol if m.isPublic => m -> m.typeSignatureIn(vType) } methods collect { // Since m is a MethodSymbol, we can do it like this instead: case (m, mt) if m.returnType == IntType => m -> mt }}

scala.reflect – Types and Symbolsdef intMethods[T : TypeTag](v: T) = { val IntType = typeOf[Int] val vType = typeOf[T] val methods = vType.members.collect { case m: MethodSymbol if m.isPublic => m -> m.typeSignatureIn(vType) } methods collect { // Actually, you need this to account for type aliases: case (m, mt) if m.returnType =:= IntType => m -> mt }}

scala.reflect – Tree Tree children • Tree • Tree Type Position Symbol • ... • Tree TypTree TermTree

scala.reflect – Tree Compiler’s internal representation of source code Immutable at runtime, made up of case classes  However, at macro time one can change its symbol, type and position Essential when writing macros Also used for annotated typed

scala.reflect – Treescala> import scala.tools.reflect.ToolBoximport scala.tools.reflect.ToolBoxscala> import scala.reflect.runtime.{currentMirror => m}import scala.reflect.runtime.{currentMirror=>m}scala> val tb = m.mkToolBox()tb: scala.tools.reflect.ToolBox[reflect.runtime.universe.type] =scala.tools.reflect.ToolBoxFactory$ToolBoxImpl@5bbdee69scala> val tree = tb.parseExpr("1 to 3 map (_+1)")tree: tb.u.Tree = 1.to(3).map(((x$1) => x$1.$plus(1)))scala> val eval = tb.runExpr(tree)eval: Any = Vector(2, 3, 4)

scala.reflect – Treescala> import scala.reflect.runtime.universe._import scala.reflect.runtime.universe._scala> showRaw(reify({ def f(x: Int, y: Int) = x + y }).tree)res4: String = Block(List(DefDef(Modifiers(), newTermName("f"),List(), List(List(ValDef(Modifiers(PARAM), newTermName("x"), Ident(scala.Int),EmptyTree), ValDef(Modifiers(PARAM), newTermName("y"), Ident(scala.Int), EmptyTree))),TypeTree(), Apply(Select(Ident(newTermName("x")), newTermName("$plus")),List(Ident(newTermName("y")))))), Literal(Constant(())))

scala.reflect – Mirror InstanceMirror ClassMirror MethodMirror ClassMirror FieldMirror MethodMirror ModuleMirror (constructors)

scala.reflect – Mirror Mirrors allow one to manipulate classes and instances at run time Each Universe may have one or mirrors Each mirror is tied to a class loader Classes with the same name may be loaded by distinct class loaders Mirrors allows reflection over the Scala language, instead of its JVM implementation

scala.reflect – Mirrorval obj = "String"val objClass = obj.getClassval classClassLoader = objClass.getClassLoaderval classLoaderMirror = runtimeMirror(classClassLoader)val classSymbol = classLoaderMirror.classSymbol(objClass)val classType = classSymbol.typeSignatureval methodName = newTermName("length")val methodSymbol = classType.member(methodName).asMethodSymbolval instanceMirror = classLoaderMirror.reflect(obj)val methodMirror = instanceMirror.reflectMethod(methodSymbol)methodMirror.apply() // == (obj.length: Any)

Actors and Akka The standard actors library will be removed  Replaced by Akka’s Akka will be part of 2.10’s distribution  Only binaries – source code will remain apart  The old library will also be available, on a separate jar There is a migration guide:  http://docs.scala-lang.org/overviews/core/actors-migration-guide.html The standard actors has a migration kit  This provides a layer over standard and Akka actors to make them source code compatible with each other

Wild Speculations untyped macros  for { val x = 0; x < 10; x += 1 } println(x) macro types  class X extends MacroClassY(parm) macro annotations  @memoize def fat(n: Int) = if (n > 0) n * fat(n -1) else 1 effect system abstract types/type parameters unification pre-processor (DOA!)

Other presentations Alex Boisvert’s Scala Roadmap:  https://speakerdeck.com/u/boia01/p/scala-roadmap-as- of-april-2012  Goes into much more depth about “distant future” Simon Ochsenreither’s What’s New in 2.10  http://ochsenreither.posterous.com/whats-new-in-210  No explanations, but more comprehensive, and links to commits

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Scala 2.10.0 (english version)

by Daniel Sobral on Jul 07, 2012

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Scala 2.10.0 (english version) Presentation Transcript