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  • What is/are the Scala way(s) to implement this Java "byte[] to Hex" class

    - by nicerobot
    I'm specifically interested in Scala (2.8) techniques for building strings with formats as well as interesting ways to make such a capability easily accessible where it's useful (lists of bytes, String, ...?).. public class Hex { public static String valueOf (final byte buf[]) { if (null == buf) { return null; } final StringBuilder sb = new StringBuilder(buf.length * 2); for (final byte b : buf) { sb.append(String.format("%02X", b & 0xff)); } return sb.toString(); } public static String valueOf (final Byteable o) { return valueOf(o.toByteArray()); } } This is only a learning exercise (so the utility and implementation of the Java isn't a concern.) Thanks

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  • Typeclass instances for unnamed types in Scala

    - by ncreep
    How would one encode the following constraint in Scala (pseudocode)? def foo(x: T forSome { type T has a Numeric[T] instance in scope }) = { val n= implicitly[...] // obtain the Numeric instance for x n.negate(x) // and use it with x } In words: I need a type class instance for my input argument, but I don't care about the argument's type, I just need to obtain the instance and use it on my argument. It doesn't have to be an existential type, but I need to avoid type parameters in the def's signature. Thanks.

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  • Scala importing a file in all files of a package

    - by Core_Dumped
    I need to use an implicit ordering that has been defined in an object in a file abc in the following way: object abc{ implicit def localTimeOrdering: Ordering[LocalDate] = Ordering.fromLessThan(_.isBefore(_)) } So, I make a package object xyz inside a file 'package.scala' that in turn is in the package 'xyz' that has files in which I need the implicit ordering to be applicable. I write something like this: package object xyz{ import abc._ } It does not seem to work. If I manually write the implicit definition statement inside the package object, it works perfectly. What is the correct way to import the object (abc) such that all of its objects/classes/definitions can be used in my entire package 'xyz' ?

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  • The Scala way to use one actor per socket connection

    - by Stefan
    I am wondering how it is possible to avoid one socket connection pr. thread in Scala. I have thought a lot about it, but I always end up with some code which is listening for incoming data for each client connection. The problem is that I want to develop an application which should simultanously handle perhaps a couple of thousand connections. However I will of course not want to create a thread for each connection because of the lack of scalability and context switching. What would be the "right" way to do this. In my world it should be possible to have one actor for each connection without the need to block one thread per actor.

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  • How to combine Option values in Scala?

    - by Jeff
    Hi! I want to be able to apply an operation f: (T,T) => T to two Option[T] values in Scala. I want the result to be None if any of the two values is None. More specifically, I want to know if is there a shorter way to do the following: def opt_apply[T](f: (T,T) => T, x: Option[T], y: Option[T]): Option[T] = { (x,y) match { case (Some(u),Some(v)) => Some(f(u,v)) case _ => None } } I have tryied (x zip y) map {case (u,v) => f(u,v)} but the result is an Iterator[T] not an Option[T]. Any help will be appreciated. Thanks.

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  • Pattern matching against Scala Map type

    - by Tom Morris
    Imagine I have a Map[String, String] in Scala. I want to match against the full set of key–value pairings in the map. Something like this ought to be possible val record = Map("amenity" -> "restaurant", "cuisine" -> "chinese", "name" -> "Golden Palace") record match { case Map("amenity" -> "restaurant", "cuisine" -> "chinese") => "a Chinese restaurant" case Map("amenity" -> "restaurant", "cuisine" -> "italian") => "an Italian restaurant" case Map("amenity" -> "restaurant") => "some other restaurant" case _ => "something else entirely" } The compiler complains thulsy: error: value Map is not a case class constructor, nor does it have an unapply/unapplySeq method What currently is the best way to pattern match for key–value combinations in a Map?

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  • [Scala] Applying overloaded, typed methods on a collection

    - by stephanos
    I'm quite new to Scala and struggling with the following: I have database objects (type of BaseDoc) and value objects (type of BaseVO). Now there are multiple convert methods (all called 'convert') that take an instance of an object and convert it to the other type accordingly - like this: def convert(doc: ClickDoc): ClickVO = ... def convert(doc: PointDoc): PointVO = ... def convert(doc: WindowDoc): WindowVO = ... Now I sometimes need to convert a list of objects. How would I do this - I tried: def convert[D <: BaseDoc, V <: BaseVO](docs: List[D]):List[V] = docs match { case List() => List() case xs => xs.map(doc => convert(doc)) } Which results in 'overloaded method value convert with alternatives ...'. I tried to add manifest information to it, but couldn't make it work. I couldn't even create one method for each because it'd say that they have the same parameter type after type erasure (List). Ideas welcome!

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  • Scala updating/creating value in a hashmap

    - by user1672739
    I don't understand this with Scala hasmaps: How do I create a value or update one if it does not exist? I am tryng to count the number of characters in a list of Strings. I've tried this code but it doesn't work : def times(chars: List[Char]): List[(Char, Int)] = { val map = new HashMap[Char, Int]() chars.foreach( (c : Char) => { map.update(c, map.get(c) + 1) }) } I understand the returning type isn't correct. But is my foreach loop wrong? Is there a prettier way to write it?

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  • How to test if Scala combinator parser matches a string

    - by W.P. McNeill
    I have a Scala combinator parser that handles comma-delimited lists of decimal numbers. object NumberListParser extends RegexParsers { def number: Parser[Double] = """\d+(\.\d*)?""".r ^^ (_.toDouble) def numbers: Parser[List[Double]] = rep1sep(number, ",") def itMatches(s: String): Boolean = parseAll(numbers, s) match { case _: Success[_] => true case _ => false } } The itMatches function returns true when given a string that matches the pattern. For example: NumberListParser.itMatches("12.4,3.141") // returns true NumberListParser.itMatches("bogus") // returns false Is there a more terse way to do this? I couldn't find one in the documentation, but my function sees a bit verbose, so I wonder if I'm overlooking something.

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  • Automatic conversion between methods and functions in Scala

    - by fikovnik
    I would like to understand the rules when can Scala automatically convert methods into functions. For example, if I have following two methods: def d1(a: Int, b: Int) {} def r[A, B](delegate: (A, B) ? Unit) {} I can do this: r(d1) But, when overloading r it will no longer work: def r[A, B, C](delegate: (A, B, C) ? Unit) {} r(d1) // no longer compiles and I have to explicitly convert method into partially applied function: r(d1 _) Is there any way to accomplish following with the explicit conversion? def r[A, B](delegate: (A, B) ? Unit) {} def r[A, B, C](delegate: (A, B, C) ? Unit) {} def d1(a: Int, b: Int) {} def d2(a: Int, b: Int, c: Int) {} r(d1) // only compiles with r(d1 _) r(d2) // only compiles with r(d2 _) There is somewhat similar question, but it is not fully explained.

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  • How to place jedit-dialogs into a tag in awesome-wm?

    - by Mnementh
    I use awesome-wm and jEdit. I placed jEdit into tag '4' with the following rule in rc.lua: { rule = { class = "org-gjt-sp-jedit-jEdit" }, properties = { tag = tags[1][4] } } That works fine for the main window, but if I open an dialog for jEdit (open-file, search etc.) it opens in the tag for any other application. I used xprop, but it says the class is also "org-gjt-sp-jedit-jEdit". So how can I configure that?

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  • Wind and Water: Puzzle Battles – An Awesome Game for Linux and Windows

    - by Asian Angel
    Are you looking for a fun new game to add to your Linux or Windows systems? Then Wind and Water: Puzzle Battles could be just the game you are looking for. This awesome game comes with three distinct game modes (Story, Arcade, and Puzzle) to please the gamer within. You will need to select a language when Wind and Water starts up. Use your arrow keys to make your selection and press Enter. There will be a short intro video and then you can begin playing the game. There is a nice Tutorial Mode to help you become familiar with game play. Once you have entered your name you can choose the game mode that you want to play. Have fun as you work your way through the game! Note: Use the four Arrow Keys, the S Key, and the A Key to play Wind and Water. Wind and Water Homepage (Windows Version Download) Download the Linux Versions *Includes installation instructions for non-Ubuntu systems at bottom of the post. [via Ubuntu Vibes] Latest Features How-To Geek ETC Should You Delete Windows 7 Service Pack Backup Files to Save Space? What Can Super Mario Teach Us About Graphics Technology? Windows 7 Service Pack 1 is Released: But Should You Install It? How To Make Hundreds of Complex Photo Edits in Seconds With Photoshop Actions How to Enable User-Specific Wireless Networks in Windows 7 How to Use Google Chrome as Your Default PDF Reader (the Easy Way) Reclaim Vertical UI Space by Moving Your Tabs to the Side in Firefox Wind and Water: Puzzle Battles – An Awesome Game for Linux and Windows How Star Wars Changed the World [Infographic] Tabs Visual Manager Adds Thumbnailed Tab Switching to Chrome Daisies and Rye Swaying in the Summer Wind Wallpaper Read On Phone Pushes Data from Your Desktop to the Appropriate Android App

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  • Awesome 10 Meter Curved Touchscreen at the University of Groningen [Video]

    - by Asian Angel
    Think that you have seen awesome touchscreen setups before? Then think again because the University of Groningen has put together the ultimate version with a super-sized 10 meter curved screen setup housed at their reality center. To learn more about the assorted hardware and software used in the creation of this touchscreen wonder see the detailed information section on the YouTube page (link provided below). Note: The video has approximately 1 minute of “blank” airplay at the end. Reality touchscreen University of Groningen [via Geeks are Sexy] Latest Features How-To Geek ETC Learn To Adjust Contrast Like a Pro in Photoshop, GIMP, and Paint.NET Have You Ever Wondered How Your Operating System Got Its Name? Should You Delete Windows 7 Service Pack Backup Files to Save Space? What Can Super Mario Teach Us About Graphics Technology? Windows 7 Service Pack 1 is Released: But Should You Install It? How To Make Hundreds of Complex Photo Edits in Seconds With Photoshop Actions Awesome 10 Meter Curved Touchscreen at the University of Groningen [Video] TV Antenna Helper Makes HDTV Antenna Calibration a Snap Turn a Green Laser into a Microscope Projector [Science] The Open Road Awaits [Wallpaper] N64oid Brings N64 Emulation to Android Devices Super-Charge GIMP’s Image Editing Capabilities with G’MIC [Cross-Platform]

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  • The Citroen GT – An Awesome Video Game Car Brought to Life [Video]

    - by Asian Angel
    If you are familiar with the Gran Turismo 5 video game releases, then you will definitely recognize the Citroen GT. French automaker Citroen and Japanese racing simulation developer Polyphony Digital decided to take things one step further and collaborated to bring this awesome car to life. Then they turned it loose on the streets of London! Citroen GT on the Streets of London (HD) [via BoingBoing] You can learn more about the Citroen GT, car show appearances, and more at Wikipedia: GT by Citroen Latest Features How-To Geek ETC How to Enable User-Specific Wireless Networks in Windows 7 How to Use Google Chrome as Your Default PDF Reader (the Easy Way) How To Remove People and Objects From Photographs In Photoshop Ask How-To Geek: How Can I Monitor My Bandwidth Usage? Internet Explorer 9 RC Now Available: Here’s the Most Interesting New Stuff Here’s a Super Simple Trick to Defeating Fake Anti-Virus Malware The Citroen GT – An Awesome Video Game Car Brought to Life [Video] Final Man vs. Machine Round of Jeopardy Unfolds; Watson Dominates Give Chromium-Based Browser Desktop Notifications a Native System Look in Ubuntu Chrome Time Track Is a Simple Task Time Tracker Google Sky Map Turns Your Android Phone into a Digital Telescope Walking Through a Seaside Village Wallpaper

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  • NoSuchMethod exception when using scala Regex class... confused...

    - by hbatista
    Hi there, I have a simple Scala project that runs without any problems inside Eclipse, however, when packaged into a .jar I receive this exception when running it: Exception in thread "AWT-EventQueue-0" java.lang.NoSuchMethodError: scala.util.matching.Regex.replaceAllIn(Ljava/lang/CharSequence;Lscala/Function1;)Ljava/lang/String; What is going on here?... The code line in question, and the full stack are below. This is the offending line: "alt=\"[^>]+\">".r.replaceAllIn(inputStr, {_.replace(">", "/>")}) Full stack: Exception in thread "AWT-EventQueue-0" java.lang.NoSuchMethodError: scala.util.matching.Regex.replaceAllIn(Ljava/lang/CharSequence;Lscala/Function1;)Ljava/lang/String; at com.inosat.fuel.FuelStationDgge.fixhtml(FuelStationDgge.scala:40) at com.inosat.fuel.FuelStationDgge.setDetails(FuelStationDgge.scala:82) at com.inosat.fuel.DggeParser$$anon$1.propertyChange(DggeParser.scala:49) at java.beans.PropertyChangeSupport.firePropertyChange(Unknown Source) at java.beans.PropertyChangeSupport.firePropertyChange(Unknown Source) at java.beans.PropertyChangeSupport.firePropertyChange(Unknown Source) at org.jdesktop.beans.AbstractBean.firePropertyChange(AbstractBean.java:302) at org.jdesktop.http.async.AsyncHttpRequest.setReadyState(AsyncHttpRequest.java:705) at org.jdesktop.http.async.AsyncHttpRequest.access$600(AsyncHttpRequest.java:79) at org.jdesktop.http.async.AsyncHttpRequest$AsyncWorker.done(AsyncHttpRequest.java:831) at javax.swing.SwingWorker$5.run(Unknown Source) at javax.swing.SwingWorker$DoSubmitAccumulativeRunnable.run(Unknown Source) at sun.swing.AccumulativeRunnable.run(Unknown Source) at javax.swing.SwingWorker$DoSubmitAccumulativeRunnable.actionPerformed(Unknown Source) at javax.swing.Timer.fireActionPerformed(Unknown Source) at javax.swing.Timer$DoPostEvent.run(Unknown Source) at java.awt.event.InvocationEvent.dispatch(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)

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  • Need help figuring out scala compiler errors.

    - by klactose
    Hello all, I have been working on a project in scala, but I am getting some error messages that I don't quite understand. The classes that I am working with are relatively simple. For example: abstract class Shape case class Point(x: Int, y: Int) extends Shape case class Polygon(points: Point*) extends Shape Now suppose that I create a Polygon: val poly = new Polygon(new Point(2,5), new Point(7,0), new Point(3,1)) Then if I attempt to determine the location and size of the smallest possible rectangle that could contain the polygon, I get various errors that I don't quite understand. Below are snippets of different attempts and the corresponding error messages that they produce. val upperLeftX = poly.points.reduceLeft(Math.min(_.x, _.x)) Gives the error: "missing parameter type for expanded function ((x$1) = x$1.x)" val upperLeftX = poly.points.reduceLeft((a: Point, b: Point) => (Math.min(a.x, b.x))) Gives this error: "type mismatch; found : (Point, Point) = Int required: (Any, Point) = Any" I am very confused about both of these error messages. If anyone could explain more clearly what I am doing incorrectly, I would really appreciate it. Yes, I see that the second error says that I need type "Any" but I don't understand exactly how to implement a change that would work as I need it. Obviously simply changing "a: Point" to "a: Any" is not a viable solution, so what am I missing?

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  • Using Scala structural types with abstract types

    - by Joshua Hartman
    I'm trying to define a structural type defining anything that has an "add" method (for instance, a java collection or a java map). Using this, I want to define a few higher order functions that operate on a certain collection object GenericTypes { type GenericCollection[T] = { def add(value: T): java.lang.Boolean} } import GenericTypes._ trait HigherOrderFunctions[T, CollectionType[X] <: GenericCollection[X]] { def map[V](fn: (T) => V): CollectionType[V] .... } class RichJList[T](list: List[T]) extends HigherOrderFunctions[T, java.util.List] This does not compile with the following error error: Parameter type in structural refinement may not refer to abstract type defined outside that same refinement I tried removing the parameter on GenericCollection and putting it on the method: object GenericTypes { type GenericCollection = { def add[T](value: T): java.lang.Boolean} } import GenericTypes._ trait HigherOrderFunctions[T, CollectionType[X] <: GenericCollection] class RichJList[T](list: List[T]) extends HigherOrderFunctions[T, java.util.List] but I get another error: error: type arguments [T,java.util.List] do not conform to trait HigherOrderFunctions's type parameter bounds [T,CollectionType[X] <: org.scala_tools.javautils.j2s.GenericTypes.GenericCollection] Can anyone give me some advice on how to use structural typing with abstract typed parameters in Scala? Or how to achieve what I'm looking to accomplish? Thanks so much!

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  • Accessing type members outside the class in Scala

    - by Pekka Mattila
    Hi, I am trying to understand type members in Scala. I wrote a simple example that tries to explain my question. First, I created two classes for types: class BaseclassForTypes class OwnType extends BaseclassForTypes Then, I defined an abstract type member in trait and then defined the type member in a concerete class: trait ScalaTypesTest { type T <: BaseclassForTypes def returnType: T } class ScalaTypesTestImpl extends ScalaTypesTest { type T = OwnType override def returnType: T = { new T } } Then, I want to access the type member (yes, the type is not needed here, but this explains my question). Both examples work. Solution 1. Declaring the type, but the problem here is that it does not use the type member and the type information is duplicated (caller and callee). val typeTest = new ScalaTypesTestImpl val typeObject:OwnType = typeTest.returnType // declare the type second time here true must beTrue Solution 2. Initializing the class and using the type through the object. I don't like this, since the class needs to be initialized val typeTest = new ScalaTypesTestImpl val typeObject:typeTest.T = typeTest.returnType // through an instance true must beTrue So, is there a better way of doing this or are type members meant to be used only with the internal implementation of a class?

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  • Dependency between operations in scala actors

    - by paradigmatic
    I am trying to parallelise a code using scala actors. That is my first real code with actors, but I have some experience with Java Mulithreading and MPI in C. However I am completely lost. The workflow I want to realise is a circular pipeline and can be described as the following: Each worker actor has a reference to another one, thus forming a circle There is a coordinator actor which can trigger a computation by sending a StartWork() message When a worker receives a StartWork() message, it process some stuff locally and sends DoWork(...) message to its neighbour in the circle. The neighbours do some other stuff and sends in turn a DoWork(...) message to its own neighbour. This continues until the initial worker receives a DoWork() message. The coordinator can send a GetResult() message to the initial worker and wait for a reply. The point is that the coordinator should only receive a result when data is ready. How can a worker wait that the job returned to it before answering the GetResult() message ? To speed up computation, any worker can receive a StartWork() at any time. Here is my first try pseudo-implementation of the worker: class Worker( neighbor: Worker, numWorkers: Int ) { var ready = Foo() def act() { case StartWork() => { val someData = doStuff() neighbor ! DoWork( someData, numWorkers-1 ) } case DoWork( resultData, remaining ) => if( remaining == 0 ) { ready = resultData } else { val someOtherData = doOtherStuff( resultData ) neighbor ! DoWork( someOtherData, remaining-1 ) } case GetResult() => reply( ready ) } } On the coordinator side: worker ! StartWork() val result = worker !? GetResult() // should wait

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  • initialising a 2-dim Array in Scala

    - by Stefan W.
    (Scala 2.7.7:) I don't get used to 2d-Arrays. Arrays are mutable, but how do I specify a 2d-Array which is - let's say of size 3x4. The dimension (2D) is fixed, but the size per dimension shall be initializable. I tried this: class Field (val rows: Int, val cols: Int, sc: java.util.Scanner) { var field = new Array [Char](rows)(cols) for (r <- (1 to rows)) { val line = sc.nextLine () val spl = line.split (" ") field (r) = spl.map (_.charAt (0)) } def put (val rows: Int, val cols: Int, c: Char) = todo () } I get this error: :11: error: value update is not a member of Char field (r) = spl.map (_.charAt (0)) If it would be Java, it would be much more code, but I would know how to do it, so I show what I mean: public class Field { private char[][] field; public Field (int rows, int cols, java.util.Scanner sc) { field = new char [rows][cols]; for (int r = 0; r < rows; ++r) { String line = sc.nextLine (); String[] spl = line.split (" "); for (int c = 0; c < cols; ++c) field [r][c] = spl[c].charAt (0); } } public static void main (String args[]) { new Field (3, 4, new java.util.Scanner ("fraese.fld")); } } and fraese.fld would look, for example, like that: M M M M . M I get some steps wide with val field = new Array Array [Char] but how would I then implement 'put'? Or is there a better way to implement the 2D-Array. Yes, I could use a one-dim-Array, and work with put (y, x, c) = field (y * width + x) = c but I would prefer a notation which looks more 2d-ish.

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  • How to store child objects on GAE using JDO from Scala

    - by Gero
    Hi, I'm have a parent-child relation between 2 classes, but the child objects are never stored. I do get an warning: "org.datanucleus.store.appengine.MetaDataValidator checkForIllegalChildField: Unable to validate relation net.vermaas.kivanotify.model.UserCriteria.internalCriteria" but it is unclear to me why this occurs. Already tried several alternatives without luck. The parent class is "UserCriteria" which has a List of "Criteria" as children. The classes are defined as follows (Scala): class UserCriteria(tu: String, crit: Map[String, String]) extends LogHelper { @PrimaryKey @Persistent{val valueStrategy = IdGeneratorStrategy.IDENTITY} var id = KeyFactory.createKey("UserCriteria", System.nanoTime) @Persistent var twitterUser = tu @Persistent var internalCriteria: java.util.List[Criteria] = flatten(crit) def flatten(crits: Map[String, String]) : java.util.List[Criteria] = { val list = new java.util.ArrayList[Criteria] for (key <- crits.keySet) { list.add(new Criteria(this, key, crits(key))) } list } def criteria: Map[String, String] = { val crits = mutable.Map.empty[String, String] for (i <- 0 to internalCriteria.size-1) { crits(internalCriteria.get(i).name) = internalCriteria.get(i).value } Map.empty ++ crits } // Stripped the equals, canEquals, hashCode, toString code to keep the code snippet short... } @PersistenceCapable @EmbeddedOnly class Criteria(uc: UserCriteria, nm: String, vl: String) { @Persistent var userCriteria = uc @Persistent var name = nm @Persistent var value = vl override def toString = { "Criteria name: " + name + " value: " + value } } Any ideas why the childs are not stored? Or why I get the error message? Thanks, Gero

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  • Trait, FunctionN, or trait-inheriting-FunctionN in Scala?

    - by Willis Blackburn
    I have a trait in Scala that has a single method. Call it Computable and the single method is compute(input: Int): Int. I can't figure out whether I should Leave it as a standalone trait with a single method. Inherit from (Int = Int) and rename "compute" to "apply." Just get rid of Computable and use (Int = Int). A factor in favor of it being a trait is that I could usefully add some additional methods. But of course if they were all implemented in terms of the compute method then I could just break them out into a separate object. A factor in favor of just using the function type is simplicity and the fact that the syntax for an anonymous function is more concise than that for an anonymous Computable instance. But then I've no way to distinguish objects that are actually Computable instances from other functions that map Int to Int but aren't meant to be used in the same context as Computable. How do other people approach this type of problem? No right or wrong answers here; I'm just looking for advice.

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  • Doesn't (didn't) Scala have automatically generated setters?

    - by Malvolio
    Google and my failing memory are both giving me hints that it does, but every attempt is coming up dry. class Y { var y = 0 } var m = new Y() m.y_(3) error: value y_ is not a member of Y Please tell me I am doing something wrong. (Also: please tell me what it is I am doing wrong.) EDIT The thing I am not doing wrong, or at least not the only thing I am doing wrong, is the way I am invoking the setter. The following things also fail, all with the same error message: m.y_ // should be a function valued expression m.y_ = (3) // suggested by Google and by Mchl f(m.y_) // where f takes Int => Unit as an argument f(m.y) // complains that I am passing in Int not a function I am doing this all through SimplyScala, because I'm too lazy and impatient to set up Scala on my tiny home machine. Hope it isn't that... And the winner is ... Fabian, who pointed out that I can't have a space between the _ and the =. I thought out why this should be and then it occurred to me: The name of the setter for y is not y_, it is y_= ! Observe: class Y { var y = 0 } var m = new Y() m.y_=(3) m.y res1: Int = 3 m.y_= error: missing arguments for method y_= in class Y; follow this method with `_` if you want to treat it as a partially applied function m.y_= ^ m.y_=_ res2: (Int) => Unit = def four(f : Int => Unit) = f(4) four(m.y_=) m.y res3: Int = 4 Another successful day on StackExchange.

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  • Implicit conversion between Scala collection types

    - by ebruchez
    I would like to implicitly convert between the Scala XML Elem object and another representation of an XML element, in my case dom4j Element. I wrote the following implicit conversions: implicit def elemToElement(e: Elem): Element = ... do conversion here ... implicit def elementToElem(e: Element): Elem = ... do conversion here ... So far so good, this works. Now I also need collections of said elements to convert both ways. First, do I absolutely need to write additional conversion methods? Things didn't seem to work if I didn't. I tried to write the following: implicit def elemTToElementT(t: Traversable[Elem]) = t map (elemToElement(_)) implicit def elementTToElemT(t: Traversable[Element]) = t map (elementToElem(_)) This doesn't look too ideal because if the conversion method takes a Traversable, then it also returns a Traversable. If I pass a List, I also get a Traversable out. So I assume the conversion should be parametrized somehow. So what's the standard way of writing these conversions in order to be as generic as possible?

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  • Scala always returning true....WHY?

    - by jhamm
    I am trying to learn Scala and am a newbie. I know that this is not optimal functional code and welcome any advice that anyone can give me, but I want to understand why I keep getting true for this function. def balance(chars: List[Char]): Boolean = { val newList = chars.filter(x => x.equals('(') || x.equals(')')); return countParams(newList, 0) } def countParams(xs: List[Char], y: Int): Boolean = { println(y + " right Here") if (y < 0) { println(y + " Here") return false } else { println(y + " Greater than 0") if (xs.size > 0) { println(xs.size + " this is the size") xs match { case xs if (xs.head.equals('(')) => countParams(xs.tail, y + 1) case xs if (xs.head.equals(')')) => countParams(xs.tail, y - 1) case xs => 0 } } } return true; } balance("()())))".toList) I know that I am hitting the false branch of my if statement, but it still returns true at the end of my function. Please help me understand. Thanks.

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