Scala 2.10.0 (english version)

What's new with Scala 2.10.0? A brief look at the past, and a detailed look at what's coming down the pipeline.

Note: at the time this presentation was created, Scala 2.10.0 had not been released yet. The final version will probably differ in some ways.

Last update: September 20th

Transcript

1. Where did we came from, and where are we going to? Daniel Capó Sobral Last revision: Jan 05, 2013
2. 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;
3. 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
4. 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
5. 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.
6. Summary  History  Near Future  Versioning  Release Process  Bug fixes  Enhancements  SIPs (Scala Improvement Process)  Reflection  Actors and Akka  Distant Future
8. Release History • 2.9.2 2012 • 2.9.0 • 2.9.1 • 2.8.2 2011 • 2.8.0 • 2.8.1 2010 • 2.7.3 • 2.7.4 • 2.7.5 • 2.7.6 • 2.7.7 2009 • 2.7.1 • 2.7.2 2008 • 2.3.2 • 2.3.3 • 2.4.0 • 2.5.0 • 2.5.1 • 2.6.0 • 2.6.1 2007 • 2.0.0 • 2.1.0 • 2.1.1 • 2.1.2 • 2.1.3 • 2.1.5 • 2.1.6 • 2.1.7 • 2.1.8 • 2.2.0 • 2.3.0 • 2.3.1 2006 • 1.4.0 2005 • 1.0.0 • 1.1.0 • 1.1.0 • 1.1.1 • 1.2.0 • 1.3.0 2004 • 0.8.1 • 0.8.2 • 0.9.0 • 0.9.1 2003
9. Some important landmarks 2006 • Scalac written in Scala • Implicits • Traits e linearization • Multilline Strings 2007 • Extractors • Private/protected primary constructors • Private[this] • Placeholder parameters • Early Initialization • Abstract Type Constructors • Existential Types • Lazy values • Structural Types 2008 • Java Generics • Case Class Extractors 2010 • New Collections Design • Binary Compatibility of Minor Releases 2011 • Parallel Collections Not comprehensive, by any means!
11. Explaining Versioning 2 Epoch .9 Major .1 Minor -1 Bug fix
12. 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
13. Examples of New Deprecations  Octal numbers!  Double ending in dot scala> 077 <console>:1: warning: Treating numbers with a leading zero as octal is deprecated. 077 ^ res10: Int = 63 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
14. Examples of removal of deprecated features  Language syntax  Class  Method  Package for ( val i <- 1 to 10) println(i) scala.collection.mutable.CloneableCollection scala.collection.immutable.Queue.+ scala.testing.SUnit
15. Improvements of the release process  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
16. 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.
17. Closed Tickets 102 451 490 622 896 963 1118 1133 1195 1201 1247 1336 1430 1431 1432 1439 1510 1785 1799 2089 2094 2171 2196 2308 2322 2337 2388 2405 2435 2442 2460 2764 2782 2807 3047 3048 3098 3240 3272 3326 3343 3371 3392 3481 3566 3569 3628 3702 3708 3718 3755 3758 3761 3770 3798 3853 3854 3880 3898 3929 3960 3999 4018 4019 4025 4027 4063 4070 4098 4110 4124 4134 4147 4171 4172 4176 4216 4262 4270 4271 4273 4319 4326 4336 4355 4372 4391 4398 4417 4419 4425 4430 4441 4461 4467 4469 4478 4482 4490 4494 4501 4510 4512 4515 4535 4540 4541 4542 4547 4553 4561 4568 4570 4573 4574 4578 4579 4584 4592 4593 4595 4599 4601 4627 4636 4642 4647 4651 4656 4658 4661 4692 4696 4697 4709 4712 4713 4716 4717 4723 4727 4731 4737 4740 4749 4753 4757 4758 4759 4761 4764 4766 4770 4777 4780 4792
18. Closed Tickets 4794 4800 4802 4804 4807 4809 4811 4818 4823 4827 4828 4831 4833 4839 4842 4846 4851 4853 4857 4858 4859 4860 4861 4869 4871 4874 4875 4877 4879 4882 4891 4894 4898 4899 4909 4910 4911 4925 4928 4929 4933 4935 4938 4954 4957 4959 4961 4963 4970 4975 4976 4979 4981 4985 4987 4989 5005 5009 5012 5018 5020 5023 5026 5029 5032 5033 5034 5037 5040 5041 5053 5054 5056 5062 5063 5066 5071 5072 5077 5078 5080 5083 5084 5085 5093 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 5229 5230 5239 5245 5248 5256 5259 5266 5267 5272 5284 5287 5291 5293 5295 5300 5305 5313 5317 5318 5328 5334 5336 5341 5343 5344 5352 5354 5356 5358 5359 5373 5374 5375 5377 5382 5384
19. Closed Tickets (442 – July 2nd) 5387 5399 5405 5406 5407 5426 5428 5429 5441 5444 5446 5451 5452 5453 5455 5471 5488 5489 5497 5500 5510 5514 5522 5528 5530 5532 5535 5537 5542 5543 5544 5545 5552 5553 5554 5564 5571 5572 5577 5578 5580 5589 5590 5591 5593 5599 5608 5609 5610 5612 5614 5617 5623 5626 5627 5629 5632 5640 5641 5644 5648 5652 5654 5655 5656 5663 5666 5667 5672 5676 5677 5680 5682 5683 5688 5689 5690 5693 5696 5702 5703 5704 5706 5707 5708 5713 5715 5720 5728 5729 5735 5738 5742 5760 5761 5763 5769 5777 5779 5796 5801 5804 5805 5809 5816 5821 5829 5839 5840 5843 5845 5846 5853 5857 5862 5867 5879 5880 5881 5899 5910 5912 5914 5932 5953 5966 5967 5968 5971 5986 etc?
20. 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)
21. 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]  ???
22. 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
23. 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...)
24. 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)
25. IsTraversableOnce and IsTraversableLike 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???
26.  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 and IsTraversableLike
27. IsTraversableOnce and IsTraversableLike 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))
28. scala.util.Try def percentCompleted(total: Int, done: Int): Int = Try ( done * 100 / total ) getOrElse 100
29. 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 }
30. @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
31. Configurable Pools on Parallel Collections import 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()
32. Configurable Pools on Parallel Collections – Customizing class customTaskSupport extends TaskSupport { def execute[R, Tp] (task: Task[R, Tp]): () => R = ??? def executeAndWaitResult[R, Tp] (task: Task[R, Tp]): R = ??? def parallelismLevel: Int = ??? }
33. 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)
34. ???  ??? it‘s a Nothing-returning that throws exceptions  Because it’s type is Nothing, ??? may replace any expression  Excellent for stubs, exercises and presentations!
35. ??? 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/
36. ??? 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/
37. 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/
38. ScalaDoc & Implicits scaladoc -implicits
39. Class Diagrams! scaladoc -diagrams
40. Parallel Collections Docs! Available at http://docs.scala-lang.org/
41. 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 \
42. 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
43. 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
44. 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)
45. 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?
46. SIP-11: String Interpolation def hello(name: String = "world"): String = "Hello, " + name + "! " // Interpolation! def hello(name: String = "world"): String = s"Hello, $name! "
47. SIP-11: String Interpolation def percentCompleted(total: Int, done: Int): String = Try ( done * 100 / total ) map { percent => f"$percent%2d% completed" } getOrElse "100% completed" def percentCompleted(total: Int, done: Int): String = Try ( f"${ done * 100 / total }%2d% completed" ) getOrElse "100% completed"
48. SIP-11: String Interpolation: How does it work? s"Hello, $name!" // becomes StringContext("Hello, ", "!").s(name) f"${ done * 100 / total }%2d% completed" // becomes StringContext("", "%2d% completed").f(done * 100 / total) raw"String with \n in it"
49. 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, $name!\n" // newline normal  But the raw interpolator does not!  How to add/modify behavior:  Enrich My Library on StringContext  Shadowing of object StringContext  Added interpolators don’t actually need to be methods!
50. SIP-11: String Interpolation // Enrich My Library class RegexContext(sc: StringContext) { def r(args: Any*) = { sc.checkLengths(args: _*) val res = (args, sc.parts.tail).zipped map { (arg, part) => s"\\Q$arg\\E$part" } mkString "" (sc.parts.head + res).r } } implicit def toRC(sc: StringContext) = new RegexContext(sc)
51. SIP-11: String Interpolation // Interpolation nesting class RegexContext(sc: StringContext) { def r(args: Any*) = { sc.checkLengths(args: _*) s"${sc.parts.head}${ (args, sc.parts.tail).zipped map { (arg, part) => s"\\Q$arg\\E$part" } mkString "" }".r } } implicit def toRC(sc: StringContext) = new RegexContext(sc)
52. SIP-11: String Interpolation // Shadowing of StringContext object object 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!
53. SIP-11: String Interpolation // apply and unapplySeq def hello(name: String = "world"): String = i"Hello, $name!" def who(message: String): String = message match { case i"Hello, $name!" => name case _ => “no clue" } who(hello("Daniel")) == "Daniel"
54. SIP-11: String Interpolation // apply and unapplySeq implicit class SI(sc: StringContext) { object i { def apply(args: Any*): String = sc.parts.head + (args,sc.parts.tail).zipped.map(_+_).mkString def unapplySeq(s: String): Option[Seq[String]] = { val partsr = sc.parts map (p => s"\\Q$p\\E") val r = (partsr mkString "(.*)").r s match { case r(xs @ _*) => Some(xs) case _ => None } } } }
55. 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
56. SIP-13: Implicit Classes // String interpolation with Implicit Classes implicit 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 } }
57. 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
58. 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) }
59. 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) }
60. 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) }
61. SIP-14: Futures and Promises // TODO – Sorry! Examples from SIP: import scala.concurrent.{ future, promise } val p = promise[T] val f = p.future val producer = future { val r = produceSomething() p success r continueDoingSomethingUnrelated() } val consumer = future { startDoingSomething() f onSuccess { case r => doSomethingWithResult() } }
62. 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.
63. 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 } }
64. 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
65. 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!
66. 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
67. SIP-16: Macros // Typed def macros (1 to 5).foreach(println) ^ ^ | + Type check + Macro execution + New type check
68. SIP-16: Macros // Untyped def macros for {val i = 0; i < 10; i += 1} println(i) ^ ^ | | | + Arguments not type checked! + Macro execution + Type check
69. 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.
70. SIP-16: Macros // Type (class/trait) macros class User extends DbTable(jdbcUrl, “t_user”) ^ + Macro // Connects to database at compile time // and gets table description to create // class “User”
71. 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/
72. SIP-16: Macros // Macro annotations @memoize def fat(n: Int) = if (n > 0) n * fat(n – 1) else 1 // Macro applied over the annotated definition, // be it class, method, parameter, etc
73. 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
74. 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
75. 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.
76. SIP-16: Macros object 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))) } }
77. 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
78. 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...
79. SIP-17: Type Dynamic scala> class xmlPath(xml: scala.xml.Node) extends Dynamic { | def selectDynamic(path: String) = xml \\ path | } defined class xmlPath scala> new xmlPath(<root><a><b><c/></b></a></root>).b res9: scala.xml.NodeSeq = NodeSeq(<b><c/></b>)
80. SIP-17: Type Dynamic  Method call conversions:  Standard methods:  applyDynamic  Methods with named parameters:  applyDynamicNamed  Setters:  updateDynamic  Getters (nullary methods):  selectDynamic
81. 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
82.  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 Language Features
83.  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 Language Features
84.  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 Language Features
85. SIP-18: Modularizing Language Features // Postfix operator scala> "abc" length warning: there were 1 feature warnings; re-run with -feature for details res0: Int = 3
86. SIP-18: Modularizing Language Features // Postfix operator, using -feature scala> "abc" length <console>:8: warning: postfix operator length should be enabled by making the implicit value language.postfixOps visible. This can be achieved by adding the import clause 'import language.postfixOps' or by setting the compiler option -language:postfixOps. See the Scala docs for value scala.language.postfixOps for a discussion why the feature should be explicitly enabled. "abc" length ^ res0: Int = 3
87. SIP-18: Modularizing Language Features // Methods called using reflection scala> val x = new AnyRef { def hello = println("world") } x: Object{def hello: Unit} = $anon$1@7d628303 scala> x.hello <console>:10: warning: reflective access of structural type member method hello should be enabled by making the implicit value language.reflectiveCalls visible. This can be achieved by adding the import clause 'import language.reflectiveCalls' or by setting the compiler option -language:reflectiveCalls. See the Scala docs for value scala.language.reflectiveCalls for a discussion why the feature should be explicitly enabled. x.hello ^ world
88. SIP-18: Modularizing Language Features // Implicit conversions scala> implicit def f(s: String): Int = Predef.augmentString(s).toInt <console>:8: warning: implicit conversion method f should be enabled by making the implicit value language.implicitConversions visible. This can be achieved by adding the import clause 'import language.implicitConversions' or by setting the compiler option -language:implicitConversions. See the Scala docs for value scala.language.implicitConversions for a discussion why the feature should be explicitly enabled. implicit def f(s: String): Int = Predef.augmentString(s).toInt ^ f: (s: String)Int
89.  The feature being limited are implicit conversions  Other implicit usages are still allowed  Implicit conversions through implicit classes works too SIP-18: Modularizing Language Features
90. SIP-18: Modularizing Language Features // Higher Kinded Types scala> class Monad[M[_]] <console>:9: warning: higher-kinded type should be enabled by making the implicit value language.higherKinds visible. This can be achieved by adding the import clause 'import language.higherKinds' or by setting the compiler option -language:higherKinds. See the Scala docs for value scala.language.higherKinds for a discussion why the feature should be explicitly enabled. class Monad[M[_]] ^ defined class Monad
91. SIP-18: Modularizing Language Features // Existentials scala> 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 enabled by making the implicit value language.existentials visible. This can be achieved by adding the import clause 'import language.existentials' or by setting the compiler option -language:existentials. See the Scala docs for value scala.language.existentials for a discussion why the feature should be explicitly enabled. val l: List[ T forSome { type T }] = List(1) ^ l: List[T forSome { type T }] = List(1)
92. SIP-18: Modularizing Language Features // Type Dynamic TODO
93. SIP-18: Modularizing Language Features // Macros scala> def g(d: Any): Any = macro f <console>:12: error: macro definition needs to be enabled by making the implicit value language.experimental.macros visible. This can be achieved by adding the import clause 'import language.experimental.macros' or by setting the compiler option -language:experimental.macros. See the Scala docs for value scala.language.experimental.macros for a discussion why the feature needs to be explicitly enabled. def g(d: Any): Any = macro f ^
94. 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
95. scala.reflect – Universes Source: Scala Reflection Pre-SIP Notice: all of the classes on scala-library.jar depicted above were removed.
96. 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
97. 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
98. scala.reflect – Main Types Universe Name Symbol Type Tree Position AnnotationInfo FlagSet
99. scala.reflect – Name Name TermName TypeName
100. 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
101. scala.reflect – Symbol Symbol Type Symbol Type ... owner Symbol Name TermName TypeName
102. 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
103. 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
104. scala.reflect – Types and Symbols scala> 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 head scala> res1.typeSignature res2: reflect.runtime.universe.Type = => A scala> res1.typeSignatureIn(res0) res3: reflect.runtime.universe.Type = => Int
105. scala.reflect – Types and Symbols def 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 } }
106. scala.reflect – Types and Symbols def 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 } }
107. scala.reflect – Types and Symbols def 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 } }
108. scala.reflect – Tree Tree children • Tree • Tree • ... • Tree Type Position Symbol TypTree TermTree
109. 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
110. scala.reflect – Tree scala> import scala.tools.reflect.ToolBox import scala.tools.reflect.ToolBox scala> 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@5bbdee69 scala> 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)
111. scala.reflect – Tree scala> 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(ValD ef(Modifiers(PARAM), newTermName("x"), Ident(scala.Int), EmptyTree), ValDef(Modifiers( PARAM), newTermName("y"), Ident(scala.Int), EmptyTree))), TypeTree(), Apply(Select(Ide nt(newTermName("x")), newTermName("$plus")), List(Ident(newTermName("y")))))), Literal (Constant(())))
112. scala.reflect – Mirror InstanceMirror ClassMirror FieldMirror MethodMirror ModuleMirror ClassMirror MethodMirror (constructors)
113. 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
114. scala.reflect – Mirror val obj = "String" val objClass = obj.getClass val classClassLoader = objClass.getClassLoader val classLoaderMirror = runtimeMirror(classClassLoader) val classSymbol = classLoaderMirror.classSymbol(objClass) val classType = classSymbol.typeSignature val methodName = newTermName("length") val methodSymbol = classType.member(methodName).asMethodSymbol val instanceMirror = classLoaderMirror.reflect(obj) val methodMirror = instanceMirror.reflectMethod(methodSymbol) methodMirror.apply() // == (obj.length: Any)
115. 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
117. 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!)
118. 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