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  • Merging elements in a scala list

    - by scompt.com
    I'm trying to port the following Java snippet to Scala. It takes a list of MyColor objects and merges all of the ones that are within a delta of each other. It seems like a problem that could be solved elegantly using some of Scala's functional bits. Any tips? List<MyColor> mergedColors = ...; MyColor lastColor = null; for(Color aColor : lotsOfColors) { if(lastColor != null) { if(lastColor.diff(aColor) < delta) { lastColor.merge(aColor); continue; } } lastColor = aColor; mergedColors.add(aColor); }

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  • How to change attribute on Scala XML Element

    - by Dave
    I have an XML file that I would like to map some attributes of in with a script. For example: <a> <b attr1 = "100" attr2 = "50"> </a> might have attributes scaled by a factor of two: <a> <b attr1 = "200" attr2 = "100"> </a> This page has a suggestion for adding attributes but doesn't detail a way to map a current attribute with a function (this way would make that very hard): http://www.scalaclass.com/book/export/html/1 What I've come up with is to manually create the XML (non-scala) linked-list... something like: // a typical match case for running thru XML elements: case Elem(prefix, e, attributes, scope, children @ _*) => { var newAttribs = attributes for(attr <- newAttribs) attr.key match { case "attr1" => newAttribs = attribs.append(new UnprefixedAttribute("attr1", (attr.value.head.text.toFloat * 2.0f).toString, attr.next)) case "attr2" => newAttribs = attribs.append(new UnprefixedAttribute("attr2", (attr.value.head.text.toFloat * 2.0f).toString, attr.next)) case _ => } Elem(prefix, e, newAttribs, scope, updateSubNode(children) : _*) // set new attribs and process the child elements } Its hideous, wordy, and needlessly re-orders the attributes in the output, which is bad for my current project due to some bad client code. Is there a scala-esque way to do this?

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  • How are Scala closures transformed to Java objects?

    - by iguana
    I'm currently looking at closure implementations in different languages. When it comes to Scala, however, I'm unable to find any documentation on how a closure is mapped to Java objects. It is well documented that Scala functions are mapped to FunctionN objects. I assume that the reference to the free variable of the closure must be stored somewhere in that function object (as it is done in C++0x, e.g.). I also tried compiling the following with scalac and then decompiling the class files with JD: object ClosureExample extends Application { def addN(n: Int) = (a: Int) => a + n var add5 = addN(5) println(add5(20)) } In the decompiled sources, I see an anonymous subtype of Function1, which ought to be my closure. But the apply() method is empty, and the anonymous class has no fields (which could potentially store the closure variables). I suppose the decompiler didn't manage to get the interesting part out of the class files... Now to the questions: Do you know how the transformation is done exactly? Do you know where it is documented? Do you have another idea how I could solve the mystery?

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  • Scala implicit dynamic casting

    - by weakwire
    I whould like to create a scala Views helper for Android Using this combination of trait and class class ScalaView(view: View) { def onClick(action: View => Any) = view.setOnClickListener(new OnClickListener { def onClick(view: View) { action(view) } }) } trait ScalaViewTrait { implicit def view2ScalaView(view: View) = new ScalaView(view) } I'm able to write onClick() like so class MainActivity extends Activity with ScalaViewTrait { //.... val textView = new TextView(this) textView.onClick(v => v.asInstanceOf[TextView] setText ("asdas")) } My concern is that i want to avoid casting v to TextView v will always be TextView if is applied to a TextView LinearLayout if applied to LinearLayout and so on. Is there any way that v gets dynamic casted to whatever view is applied? Just started with Scala and i need your help with this. UPDATE With the help of generics the above get's like this class ScalaView[T](view: View) { def onClick(action: T => Any) = view.setOnClickListener(new OnClickListener { def onClick(view: View) { action(view.asInstanceOf[T]) } }) } trait ScalaViewTrait { implicit def view2ScalaView[T](view: View) = new ScalaView[T](view) } i can write onClick like this view2ScalaView[TextView](textView) .onClick(v => v.setText("asdas")) but is obvious that i don't have any help from explicit and i moved the problem instead or removing it

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  • Scala XML API: Why allow NodeSeq as attribute values?

    - by Synesso
    It seems attribute values are of type Seq[Node]. scala> <a b="1"/>.attribute("b") res11: Option[Seq[scala.xml.Node]] = Some(1) This means you can assign XML as an attribute value. scala> <a b={<z><x/></z>}/>.attribute("b") res16: Option[Seq[scala.xml.Node]] = Some(<z><x></x></z>) scala> <a b={<z><x/></z>}/>.attribute("b").map(_ \ "x") res17: Option[scala.xml.NodeSeq] = Some(<x></x>) scala> new xml.PrettyPrinter(120, 2).format(<a b={<z><x/></z>}/>) res19: String = <a b="<z><x></x></z>"></a> This seems funky to me. I've never seen XML as attribute values in the real world. Why is it allowed? Why is an attribute value simply not of type String?

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  • scala 2.8 CanBuildFrom

    - by oxbow_lakes
    Following on from another question I asked, I wanted to understand a bit more about the Scala method TraversableLike[A].map whose signature is as follows: def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That Notice a few things about this method: it takes a function turning each A in the traversable into a B it returns That and takes an implicit argument of type CanBuildFrom[Repr, B, That] I can call this as follows: > val s: Set[Int] = List("Paris", "London").map(_.length) s: Set[Int] Set(5,6) What I cannot quite grasp is how the fact that That is bound to B (i.e. it is some collection of B's) is being enforced by the compiler. The type parameters look to be independent in both the signature above and in the signature of the trait CanBuildFrom itself: trait CanBuildFrom[-From, -Elem, +To] How is the scala compiler ensuring that That cannot be forced into something which does not make sense? > val s: Set[String] = List("Paris", "London").map(_.length) //will not compile EDIT - this question of course boils down to: How does the compiler decide what implicit CanBuildFrom objects are in scope for the call?

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  • Lancement du forum d'entraide dédié à Scala, l'un des langages alternatifs pour la plateforme Java

    Ce nouveau forum d'entraide est destiné aux questions sur Scala. Avant de poser votre question, prenez le temps de consulter les ressources à votre disposition :Documentation officielle La catégorie Scala du blog de djo.mos Pour vos questions sur Lift, merci de privilégier le forum Autres Frameworks Web Java. Pour toute autre question sur des frameworks s'appuyant sur Scala, si vous ne trouvez pas de forum adapté à la problématique traitée, merci de privilégier le présent forum en p...

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  • Lancement du forum d'entraide dédié à Scala, l'un des langages alternatifs pour la plateforme Java

    Ce nouveau forum d'entraide est destiné aux questions sur Scala. Avant de poser votre question, prenez le temps de consulter les ressources à votre disposition :Documentation officielle La catégorie Scala du blog de djo.mos Pour vos questions sur Lift, merci de privilégier le forum Autres Frameworks Web Java. Pour toute autre question sur des frameworks s'appuyant sur Scala, si vous ne trouvez pas de forum adapté à la problématique traitée, merci de privilégier le présent forum en p...

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  • C++ vainqueur d'un benchmark avec Java, Scala et Go présenté aux Scala Days, l'étude portait sur l'implémentation d'un algorithme

    C++ vainqueur d'un benchmark avec Java, Scala et Go Présentée aux Scala Days, l'étude portait sur l'implémentation d'un algorithme Bonne nouvelle pour tous les amateurs de C++ ! Ce langage reste le plus performant et sans conteste ! Présenté au Scala Days en début de mois, un benchmark met en compétition le C++, Java, Scala et GO pour l'implémentation du même algorithme en cherchant à s'appuyer sur les éléments du langage (pas de Boost ici donc). Et C++ remporte haut la main en temps d'exécution mais aussi en empreinte mémoire. Mieux, contrairement à certaines idées reçues, les temps de compilation ou le nombre de ligne de code restent à des valeurs qui n'ont pas à rougir face à Java par exemple....

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  • Does Scala's BigDecimal violate the equals/hashCode contract?

    - by oxbow_lakes
    As the Ordered trait demands, the equals method on Scala's BigDecimal class is consistent with the ordering. However, the hashcode is simply taken from the wrapped java.math.BigDecimal and is therefore inconsistent with equals. object DecTest { def main(args: Array[String]) { val d1 = BigDecimal("2") val d2 = BigDecimal("2.00") println(d1 == d2) //prints true println(d1.hashCode == d2.hashCode) //prints false } } I can't find any reference to this being a known issue. Am I missing something?

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  • Variadic templates in Scala

    - by Thomas Jung
    Suppose you want to have something like variadic templates (the ability to define n type parameters for a generic class) in Scala. For example you do not want to define Tuple2[+T1, +T2] and Tuple3[+T1, +T2, +T3] but Tuple[T*]. Are there other options than HLists?

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  • scala jpa notifying hibernate

    - by coubeatczech
    Hi, i just tried to play a little with Scala Jpa, Downladed and run the basic lift-jpa-basic maven archetype, it works, but when I try to add my own @Entity, there is Unknown entity exception thrown. So what do I need to tell the environment to notify my entities? Thanks for answering.

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  • Scala giving me "illegal start of definition"

    - by Malvolio
    I'm trying to get started with Scala and cannot get out of the starting gate. A file consisting of the line package x gives me error: illegal start of definition Regardless of what x is and regardless of where I put the file (I had a theory that I had to place the file in a directory hierarchy to match the package definition, but no). I get the same error with the example code from the web site and with the REPL.

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  • Scala compiler says unreachable code, why?

    - by taotree
    I'm new to Scala... Here's the code: def ack2(m: BigInt, n: BigInt): BigInt = { val z = BigInt(0) (m,n) match { case (z,_) => n+1 case (_,z) => ack2(m-1,1) // Compiler says unreachable code on the paren of ack2( case _ => ack2(m-1, ack2(m, n-1)) // Compiler says unreachable code on the paren of ack2( } } I'm trying to understand that... why is it giving that error?

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  • Ant-Ivy-Scala Template: any suggestions on improvements?

    - by luigi-prog
    I just created a template project for Scala using Ant and Apache Ivy. I want to get the communitie's input on any improvements to the Template so it can be improved. The Environment effectively consists of 3 files: build.xml ivy.xml ivysettings.xml running ant init will create all needed directories. I was wondering if there are any Ant or Apache Ivy gurus around that could give some input. The Git Project is Located Here And the Project HomePage here

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  • scala for yield setting a value

    - by coubeatczech
    Hi, I want to create a list of GridBagPanel.Constraints. I read it in the scala programming book, that there is a cool for-yield construction, but I probably haven't understood the way it works correctly, because my code doesn't compile. Here it is: val d = for { i <- 0 until 4 j <- 0 until 4 } yield { c = new Constraints c.gridx = j c.gridy = i } I want to generate a List[Constraints] and for every constraint set different x,y values so later, when I later add the components, they're going to be in a grid.

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  • What is the best scala-like persistence framework available right now?

    - by egervari
    What is the best scala-like persistence framework available right now? Hibernate works, but it's not very scala-like. It insists on using annotations, no-arg constructors, doesn't work with anonymous class instances, doesn't work with scala collections, has an outdated string-based query model, etc. I'm looking for something that really fits Scala. Does it exist? Or do I have to make it?

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  • scala currying by nested functions or by multiple parameter lists

    - by Morgan Creighton
    In Scala, I can define a function with two parameter lists. def myAdd(x :Int)(y :Int) = x + y This makes it easy to define a partially applied function. val plusFive = myAdd(5) _ But, I can accomplish something similar by defining and returning a nested function. def myOtherAdd(x :Int) = { def f(y :Int) = x + y f _ } Cosmetically, I've moved the underscore, but this still feels like currying. val otherPlusFive = myOtherAdd(5) What criteria should I use to prefer one approach over the other?

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