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  • Constructor with non-instance variable assistant?

    - by Robert Fischer
    I have a number of classes that look like this: class Foo(val:BasicData) extends Bar(val) { val helper = new Helper(val) val derived1 = helper.getDerived1Value() val derived2 = helper.getDerived2Value() } ...except that I don't want to hold onto an instance of "helper" beyond the end of the constructor. In Java, I'd do something like this: public class Foo { final Derived derived1, derived2; public Foo(BasicData val) { Helper helper = new Helper(val); derived1 = helper.getDerived1Value(); derived2 = helper.getDerived2Value(); } } So how do I do something like that in Scala? I'm aware of creating a helper object of the same name of the class with an apply method: I was hoping for something slightly more succinct.

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  • Running a method after the constructor of any derived class

    - by Alexey Romanov
    Let's say I have a Java class abstract class Base { abstract void init(); ... } and I know every derived class will have to call init() after it's constructed. I could, of course, simply call it in the derived classes' constructors: class Derived1 extends Base { Derived1() { ... init(); } } class Derived2 extends Base { Derived2() { ... init(); } } but this breaks "don't repeat yourself" principle rather badly (and there are going to be many subclasses of Base). Of course, the init() call can't go into the Base() constructor, since it would be executed too early. Any ideas how to bypass this problem? I would be quite happy to see a Scala solution, too.

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  • error: polymorphic expression with default arguments

    - by 0__
    This following bugs me: trait Foo[ A ] class Bar[ A ]( set: Set[ Foo[ A ]] = Set.empty ) This yields <console>:8: error: polymorphic expression cannot be instantiated to expected type; found : [A]scala.collection.immutable.Set[A] required: Set[Foo[?]] class Bar[ A ]( set: Set[ Foo[ A ]] = Set.empty ) ^ It is quite annoying that I have to repeat the type parameter in Set.empty. Why does the type inference fail with this default argument? The following works: class Bar[ A ]( set: Set[ Foo[ A ]] = { Set.empty: Set[ Foo[ A ]]}) Please note that this has nothing to do with Set in particular: case class Hallo[ A ]() class Bar[ A ]( hallo: Hallo[ A ] = Hallo.apply ) // nope Strangely not only this works: class Bar[ A ]( hallo: Hallo[ A ] = Hallo.apply[ A ]) ...but also this: class Bar[ A ]( hallo: Hallo[ A ] = Hallo() ) // ???

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  • How to expose a constructor variable(sic!) as read-only?

    - by Malax
    Hi StackOverflow! I have this rather simple question about Scala. Given that i have to following class definition: class Foo(var bar: Int) The code which is able to construct an instance of Foo must be able to pass the initial value for bar. But if I define bar as var the User is also able to change its value at runtime which is not what I want. The User should only be able to read bar. bar itself is modified internally so a val is not an option. I think I might be getting an answer very soon as this question is so simple. :-) Cheers, Malax

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  • Sharepoint Designer XSLT count boolean node = true

    - by Heather Masters
    I have a SharePoint list I converted to XSLT to do some additional grouping and counting and percentages. I need to return the number of items = true within my nodeset, I have: <xsl:value-of select="count($nodeset/@PartnerArrivedAtCall)"/> (which returns the count of all the nodes) I have tried <xsl:value-of select="count($nodeset/@PartnerArrivedAtCall [@PartnerArrivedAtCall = 'Yes'])"/> (returns zero) and <xsl:variable name="ArrivedYes" select="$nodeset/@PartnerArrivedAtCall [@PartnerArrivedAtCall='Yes']"/> (also returns zero) Can you please give me a good example of how to count only the true values (in my XML, true = "Yes") Thanks!

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  • Adding Apache common dependency to Play Framework 2.0

    - by Mooh
    i want to import org.apache.commons.io but i'm getting this error: [info] Compiling 1 Java source to /home/ghost/Bureau/app/play-2.0.1/waf/target/scala-2.9.1/classes... [error] /home/ghost/Bureau/app/play-2.0.1/waf/app/controllers/Application.java:9: error: package org.apache.commons.io does not exist [error] import org.apache.commons.io.*; [error] ^ [error] /home/ghost/Bureau/app/play-2.0.1/waf/app/controllers/Application.java:41: error: cannot find symbol [error] FileUtils.copyFile(file, destinationFile); [error] ^ [error] symbol: variable FileUtils [error] location: class Application [error] 2 errors [error] {file:/home/ghost/Bureau/app/play-2.0.1/waf/}waf/compile:compile: javac returned nonzero exit code [error] application - Play can't find package org.apache.commons.io . How i can i add it as a dependency ?

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  • AS3 Components in Flash Designer

    - by Jack Voight
    In an ActionScript 2 project I can create a new MovieClip, right-click on it on the library and select "Component Definition" to add parameters that can be referenced inside the MovieClip. This parameters can be easily changed in the MovieClips's properties. Now, I'm working on an ActionScript 3 project but haven't been able to figure out a way to obtain the values passed in those parameters. I defined a parameter named "textToDisplay" but when I write the following in the Actions for the first frame I get an error: trace(textToDisplay); This is the error: 1120: Access of undefined property textToDisplay. Do you know how to capture the value of that parameter? Thanks PS: I'm using Adobe Flash CS3 Professional on Windows XP

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  • How to be a better software designer

    - by Bmw
    I feel as if I am a hack programmer. I do things over and over again until they finally work. I copy/paste code. I don't think about why something makes sense, if it works I go with it. I have my undergraduate in computer science, and I've done this the entire time. Somehow I made it through the degree by doing this and now I'm in my second year of programming professionally and I am still able to do this and get away with it. Here's the thing, I don't want to be this way anymore. I am not proud of the work I do, I feel like I'm just a copy/paste programmer. How do I become better? I want to be able to design something on my own without copying code. Have you ever been in this situation, if so how did you move beyond it to become a better programmer? To add some background about myself, I started as an asp.net c# programmer, now I'm doing vbscript (which actually makes my tendency to copy/paste/hack a lot worse I must say!) with classic asp…

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  • Possible to not use ID field but another column name? in Lift

    - by bstevens90
    I am connected to a oracle database from a scala/lift webapp. I have been able to successfully pull information from the database as I wished but am having one issue. For each table I want to access I am required to add an ID field so that the app will work with the trait IdPK. What mapper class or trait can I use to override this? I have been trying to find one but been unable to locate it. Figured people have not always had an ID field on every table they make that is just called ID... class DN_REC extends LongKeyedMapper[DN_REC] with IdPK { def getSingleton = DN_REC object dn_rec_id extends MappedInt(this){ } This is what I am talking about. I would like to use the dn_rec_id as my primary key as it is on the table. Thanks

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  • Ignore designer and generated files in Resharper analysis

    - by RaYell
    I've been using Resharper for a few days and I really like this tool, but there's one thing that annoys me about it and I wonder if it can be changed. I'm getting lots of issue notifications from generated code (almost 1400 in my project). I'd want to set those files as ignored so they won't be checked as you can do with StyleCop and CodeAnalysis. Unfortunatelly it looks like Resharper ignores Generated Code settings from it's options because I'm still getting the same notifications. I've tried setting a file mask (i.e. for *.resx) and add files manually to generated, but still it doesn't change anything. I don't know if it matters but I'm using VS 2010.

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  • GAE JCache NumberFormatException, will I need to write Java to avoid?

    - by Jasper
    This code below produces a NumberFormatException in this line: val cache = cf.createCache(Collections.emptyMap()) Do you see any errors? Will I need to write a Java version to avoid this, or is there a Scala way? ... import java.util.Collections import net.sf.jsr107cache._ object QueryGenerator extends ServerResource { private val log = Logger.getLogger(classOf[QueryGenerator].getName) } class QueryGenerator extends ServerResource { def getCounter(cache:Cache):long = { if (cache.containsKey("counter")) { cache.get("counter").asInstanceOf[long] } else { 0l } } @Get("html") def getHtml(): Representation = { val cf = CacheManager.getInstance().getCacheFactory() val cache = cf.createCache(Collections.emptyMap()) val counter = getCounter(cache) cache.put("counter", counter + 1) val q = QueueFactory.getQueue("query-generator") q.add(TaskOptions.Builder.url("/tasks/query-generator").method(Method.GET).countdownMillis(1000L)) QueryGenerator.log.warning(counter.toString) new StringRepresentation("QueryGenerator started!", MediaType.TEXT_HTML) } } Thanks!

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  • Setting cookie in LiftFilter

    - by Gero
    Hi, How do I set a cookie in a LiftFilter.doFilter method? I tried to set the cookie as follows (stripped some code): class AuthenticationFilter extends LiftFilter { override def doFilter(request: ServletRequest, response: ServletResponse , chain: FilterChain) { val cookie = new HTTPCookie("SomeCookie", Full("" + System.nanoTime), Empty, Full("/authentication"), Full(60 * 60 * 24 * 14), Empty, Empty) cookie.setPath("/somePath") S.addCookie(cookie) val httpResp = response.asInstanceOf[HttpServletResponse] httpResp.sendRedirect("/some/page.html") } } However, when I check the browsers cookie, no cookie is set (apart from JSESSIONID), and I know the doFilter method is being executed because of logging messages and the fact that the browser is redirected to /some/page.html. I'm using Scala 2.8, Lift 2.1-SNAPSHOT and the app is running is GAE (1.3.6, only tested on dev_appserver so far). Any ideas? Thanks, Gero

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  • is the + in += on a Map a prefix operator of =?

    - by Steve
    In the book "Programming in Scala" from Martin Odersky there is a simple example in the first chapter: var capital = Map("US" -> "Washington", "France" -> "Paris") capital += ("Japan" -> "Tokyo") The second line can also be written as capital = capital + ("Japan" -> "Tokyo") I am curious about the += notation. In the class Map, I didn't found a += method. I was able to the same behaviour in an own example like class Foo() { def +(value:String) = { println(value) this } } object Main { def main(args: Array[String]) = { var foo = new Foo() foo = foo + "bar" foo += "bar" } } I am questioning myself, why the += notation is possible. It doesn't work if the method in the class Foo is called test for example. This lead me to the prefix notation. Is the + a prefix notation for the assignment sign (=)? Can somebody explain this behaviour?

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  • What is the purpose of AnyVal?

    - by DaoWen
    I can't think of any situation where the type AnyVal would be useful, especially with the addition of the Numeric type for abstracting over Int, Long, etc. Are there any actual use cases for AnyVal, or is it just an artifact that makes the type hierarchy a bit prettier? Just to clarify, I know what AnyVal is, I just can't think of any time that I would actually need it in Scala. When would I ever need a type that encompassed Int, Character and Double? It seems like it's just there to make the type hierarchy prettier (i.e. it looks nicer to have AnyVal and AnyRef as siblings rather than having Int, Character, etc. inherit directly from Any).

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  • Generics not so generic !!

    - by Aymen
    Hi I tried to implement a generic binary search algorithm in scala. Here it is : type Ord ={ def <(x:Any):Boolean def >(x:Any):Boolean } def binSearch[T <: Ord ](x:T,start:Int,end:Int,t:Array[T]):Boolean = { if (start > end) return false val pos = (start + end ) / 2 if(t(pos)==x) true else if (t(pos) < x) binSearch(x,pos+1,end,t) else binSearch(x,start,pos-1,t) } everything is OK until I tried to actually use it (xD) : binSearch(3,0,4,Array(1,2,5,6)) the compiler is pretending that Int not a member of Ord, well what shall I do to solve this ? Thanks

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  • Aligning Form in Visual Studio 2005

    - by patrick
    I am trying to add functionality to a form in Visual Studio 2005 that extends the form to the left. However, I am unable to figure out how to change the top and left alignment of he form in the form designer. There has to be a way to change the alignment of a form in the designer, right?

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  • Extract a portion of a Qt .ui file into its own .ui file

    - by Grant Limberg
    We have a designer creating a user interface for an application. The main window has several QStackedWidgets used for in place panel switching. What I'd like to be able to do is extract each individual panel that makes up each page of the QStackedWidget into it its own .ui file. Is there an easy way to accomplish this from within Qt Designer, or are there any other tools to help accomplish this task short of redesigning all of the panels in their own .ui files?

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  • JVM segmentation faults due to "Invalid memory access of location"

    - by Dan
    I have a small project written in Scala 2.9.2 with unit tests written using ScalaTest. I use SBT for compiling and running my tests. Running sbt test on my project makes the JVM segfault regularly, but just compiling and running my project from SBT works fine. Here is the exact error message: Invalid memory access of location 0x8 rip=0x10959f3c9 [1] 11925 segmentation fault sbt I cannot locate a core dump anywhere, but would be happy to provide it if it can be obtained. Running java -version results in this: java version "1.6.0_37" Java(TM) SE Runtime Environment (build 1.6.0_37-b06-434-11M3909) Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01-434, mixed mode) But I've also got Java 7 installed (though I was never able to actually run a Java program with it, afaik). Another issue that may be related: some of my test cases contain titles including parentheses like ( and ). SBT or ScalaTest (not sure) will consequently insert square parens in the middle of the output. For example, a test case with the name (..)..(..) might suddenly look like (..[)..](..). Any help resolving these issues is much appreciated :-) EDIT: I installed the Java 7 JDK, so now java -version shows the right thing: java version "1.7.0_07" Java(TM) SE Runtime Environment (build 1.7.0_07-b10) Java HotSpot(TM) 64-Bit Server VM (build 23.3-b01, mixed mode) This also means that I now get a more detailed segfault error and a core dump: # # A fatal error has been detected by the Java Runtime Environment: # # SIGSEGV (0xb) at pc=0x000000010a71a3e3, pid=16830, tid=19459 # # JRE version: 7.0_07-b10 # Java VM: Java HotSpot(TM) 64-Bit Server VM (23.3-b01 mixed mode bsd-amd64 compressed oops) # Problematic frame: # V [libjvm.dylib+0x3cd3e3] And the dump.

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  • Does isEmpty method in Stream evaluate the whole Stream?

    - by abhin4v
    In Scala, does calling isEmtpy method on an instance of Stream class cause the stream to be evaluated completely? My code is like this: import Stream.cons private val odds: Stream[Int] = cons(3, odds.map(_ + 2)) private val primes: Stream[Int] = cons(2, odds filter isPrime) private def isPrime(n: Int): Boolean = n match { case 1 => false case 2 => true case 3 => true case 5 => true case 7 => true case x if n % 3 == 0 => false case x if n % 5 == 0 => false case x if n % 7 == 0 => false case x if (x + 1) % 6 == 0 || (x - 1) % 6 == 0 => true case x => primeDivisors(x) isEmpty } import Math.{sqrt, ceil} private def primeDivisors(n: Int) = primes takeWhile { _ <= ceil(sqrt(n))} filter {n % _ == 0 } So, does the call to isEmpty on the line case x => primeDivisors(x) isEmpty cause all the prime divisors to be evaluated or only the first one?

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  • How can I make this method more Scalalicious

    - by Neil Chambers
    I have a function that calculates the left and right node values for some collection of treeNodes given a simple node.id, node.parentId association. It's very simple and works well enough...but, well, I am wondering if there is a more idiomatic approach. Specifically is there a way to track the left/right values without using some externally tracked value but still keep the tasty recursion. /* * A tree node */ case class TreeNode(val id:String, val parentId: String){ var left: Int = 0 var right: Int = 0 } /* * a method to compute the left/right node values */ def walktree(node: TreeNode) = { /* * increment state for the inner function */ var c = 0 /* * A method to set the increment state */ def increment = { c+=1; c } // poo /* * the tasty inner method * treeNodes is a List[TreeNode] */ def walk(node: TreeNode): Unit = { node.left = increment /* * recurse on all direct descendants */ treeNodes filter( _.parentId == node.id) foreach (walk(_)) node.right = increment } walk(node) } walktree(someRootNode) Edit - The list of nodes is taken from a database. Pulling the nodes into a proper tree would take too much time. I am pulling a flat list into memory and all I have is an association via node id's as pertains to parents and children. Adding left/right node values allows me to get a snapshop of all children (and childrens children) with a single SQL query. The calculation needs to run very quickly in order to maintain data integrity should parent-child associations change (which they do very frequently). In addition to using the awesome Scala collections I've also boosted speed by using parallel processing for some pre/post filtering on the tree nodes. I wanted to find a more idiomatic way of tracking the left/right node values. After looking at the answers listed I have settled on this synthesised version: def walktree(node: TreeNode) = { def walk(node: TreeNode, counter: Int): Int = { node.left = counter node.right = treeNodes .filter( _.parentId == node.id) .foldLeft(counter+1) { (counter, curnode) => walk(curnode, counter) + 1 } node.right } walk(node,1) }

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  • howto distinguish composition and self-typing use-cases

    - by ayvango
    Scala has two instruments for expressing object composition: original self-type concept and well known trivial composition. I'm curios what situations I should use which in. There are obvious differences in their applicability. Self-type requires you to use traits. Object composition allows you to change extensions on run-time with var declaration. Leaving technical details behind I can figure two indicators to help with classification of use cases. If some object used as combinator for a complex structure such as tree or just have several similar typed parts (1 car to 4 wheels relation) than it should use composition. There is extreme opposite use case. Lets assume one trait become too big to clearly observe it and it got split. It is quite natural that you should use self-types for this case. That rules are not absolute. You may do extra work to convert code between this techniques. e.g. you may replace 4 wheels composition with self-typing over Product4. You may use Cake[T <: MyType] {part : MyType} instead of Cake { this : MyType => } for cake pattern dependencies. But both cases seem counterintuitive and give you extra work. There are plenty of boundary use cases although. One-to-one relations is very hard to decide with. Is there any simple rule to decide what kind of technique is preferable? self-type makes you classes abstract, composition makes your code verbose. self-type gives your problems with blending namespaces and also gives you extra typing for free (you got not just a cocktail of two elements but gasoline-motor oil cocktail known as a petrol bomb). How can I choose between them? What hints are there? Update: Let us discuss the following example: Adapter pattern. What benefits it has with both selt-typing and composition approaches?

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  • Why Stream/lazy val implementation using is faster than ListBuffer one

    - by anrizal
    I coded the following implementation of lazy sieve algorithms using Stream and lazy val below : def primes(): Stream[Int] = { lazy val ps = 2 #:: sieve(3) def sieve(p: Int): Stream[Int] = { p #:: sieve( Stream.from(p + 2, 2). find(i=> ps.takeWhile(j => j * j <= i). forall(i % _ > 0)).get) } ps } and the following implementation using (mutable) ListBuffer: import scala.collection.mutable.ListBuffer def primes(): Stream[Int] = { def sieve(p: Int, ps: ListBuffer[Int]): Stream[Int] = { p #:: { val nextprime = Stream.from(p + 2, 2). find(i=> ps.takeWhile(j => j * j <= i). forall(i % _ > 0)).get sieve(nextprime, ps += nextprime) } } sieve(3, ListBuffer(3))} When I did primes().takeWhile(_ < 1000000).size , the first implementation is 3 times faster than the second one. What's the explanation for this ? I edited the second version: it should have been sieve(3, ListBuffer(3)) instead of sieve(3, ListBuffer()) .

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  • Design patterns for Agent / Actor based concurrent design.

    - by nso1
    Recently i have been getting into alternative languages that support an actor/agent/shared nothing architecture - ie. scala, clojure etc (clojure also supports shared state). So far most of the documentation that I have read focus around the intro level. What I am looking for is more advanced documentation along the gang of four but instead shared nothing based. Why ? It helps to grok the change in design thinking. Simple examples are easy, but in a real world java application (single threaded) you can have object graphs with 1000's of members with complex relationships. But with agent based concurrency development it introduces a whole new set of ideas to comprehend when designing large systems. ie. Agent granularity - how much state should one agent manage - implications on performance etc or are their good patterns for mapping shared state object graphs to agent based system. tips on mapping domain models to design. Discussions not on the technology but more on how to BEST use the technology in design (real world "complex" examples would be great).

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  • Bash script to insert code from one file at a specific location in another file?

    - by Kurtosis
    I have a fileA with a snippet of code, and I need a script to insert that snippet into fileB on the line after a specific pattern. I'm trying to make the accepted answer in this thread work, but it's not, and is not giving an error so not sure why not: sed -e '/pattern/r text2insert' filewithpattern Any suggestions? pattern (insert snippet on line after): def boot { also tried escaped pattern but no luck: def\ boot\ { def\ boot\ \{ fileA snippet: LiftRules.htmlProperties.default.set((r: Req) => new Html5Properties(r.userAgent)) fileB (Boot.scala): package bootstrap.liftweb import net.liftweb._ import util._ import Helpers._ import common._ import http._ import sitemap._ import Loc._ /** * A class that's instantiated early and run. It allows the application * to modify lift's environment */ class Boot { def boot { // where to search snippet LiftRules.addToPackages("code") // Build SiteMap val entries = List( Menu.i("Home") / "index", // the simple way to declare a menu // more complex because this menu allows anything in the // /static path to be visible Menu(Loc("Static", Link(List("static"), true, "/static/index"), "Static Content"))) // set the sitemap. Note if you don't want access control for // each page, just comment this line out. LiftRules.setSiteMap(SiteMap(entries:_*)) // Use jQuery 1.4 LiftRules.jsArtifacts = net.liftweb.http.js.jquery.JQuery14Artifacts //Show the spinny image when an Ajax call starts LiftRules.ajaxStart = Full(() => LiftRules.jsArtifacts.show("ajax-loader").cmd) // Make the spinny image go away when it ends LiftRules.ajaxEnd = Full(() => LiftRules.jsArtifacts.hide("ajax-loader").cmd) // Force the request to be UTF-8 LiftRules.early.append(_.setCharacterEncoding("UTF-8")) } }

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