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  • What ORMs work well with Scala?

    - by Clinton R. Nixon
    I'm about to write a Scala command-line application that relies on a MySQL database. I've been looking around for ORMs, and am having trouble finding one that will work well. The Lift ORM looks nice, but I'm not sure it can be decoupled from the entire Lift web framework. ActiveObjects also looks OK, but the author says that it may not work well with Scala. I'm not coming to Scala from Java, so I don't know all the options. Has anyone used an ORM with Scala, and if so, what did you use and how well did it work?

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  • Scala model-view-presenter, traits

    - by Ralph
    I am a fan of Martin Fowler's (deprecated) model-view-presenter pattern. I am writing a Scala view class containing several button classes. I would like to include methods to set the action properties of the buttons, to be called by the presenter. A typical code fragment looks like this: private val aButton = new JButton def setAButtonAction(action: Action): Unit = { aButton.setAction(action) } This code is repeated for each button. If Java/Scala had the C preprocessor, I would create a macro to generate this code, given the button name (no lectures on the evils of the C preprocessor, please). This code is obviously very verbose and repetitive. Is there any better way way to do this in Scala, perhaps using traits? Please hold the lectures about scala.swing. I looking for a general pattern here.

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  • IS classOf[] in scala 2.8 different from 2.7?

    - by redtank
    I have an interface from java public class IJava { ... public java.lang.Class getType(); ... } It is inherited in Scala class CScala { def getType() = classOf[Foo] } it worked in scala 2.7.7. But in 2.8.0.RC1, i get type mismatch; found : java.lang.ClassFoo required: java.lang.Class How do i get java.langClass in Scala 2.8

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  • Practical examples of using symbols in Scala?

    - by Jesper
    Scala has symbols - names that start with a single quote ' and which are a kind of string constants. I know symbols from Ruby (where they start with a colon). In Ruby they are used for some meta-programming tasks, like generating getters and setters for member variables (for example attr_reader :name to generate a getter for name). I haven't seen a lot of use of symbols in Scala code yet. What are practical uses for symbols in Scala?

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  • Actors in Scala.net

    - by weijiajun
    I have recently completed some study of erlang, and was intrigued by scala for its feature set and the ease of interpolating with java (and possibly .net) applications. I am finally studying actors and was wondering if there is an actor mechanism that currently works in .net. I have looked at the libararies that come down with sbaz and have found that there is a scala.Concurrent but no scala.actors.Actor. I tried to use the scala.Concurrent.Channel but was unable to use the ! to send messages. I was just wondering if this is something that is currently available and if so how do you go about setting it up.

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  • Scala project does not automatically build in Eclipse

    - by stacker
    I copied the examples folder from scala-2.7.7.final-devel-docs to the src folder of a scala project. But the source files will not compiled unless I change them manually. "Project/Build automatically" is checked. I'm using the Scala Eclipse Plugin 2.7.7-final How can I achieve that this works like in java projects?

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  • Scala println in a for loop

    - by random459
    The following Scala code does just what I expect it to - it prints each line of some_file.txt. import scala.io.Source val lines = Source.fromPath("some_file.txt").mkString for (line <- lines) print(line) If I use println instead of print, I expect to see some_file.txt printed out with double-spacing. Instead, the program prints a newline after every character of some_file.txt. Could someone explain this to me? I'm using Scala 2.8.0 Beta 1.

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  • Scala 2.8.1 implicitly convert to java.util.List<java.util.Map<String, Object>>

    - by Ralph
    I have a Scala data structure created with the following: List(Map[String, Anyref]("a" -> someFoo, "b" -> someBar)) I would like to implicitly convert it (using scala.collection.JavaConversions or scala.collection.JavaConverters) to a java.util.List<java.util.Map<String, Object>> to be passed the a Java method that expects the latter. Is this possible? I have already created the following method that does it, but was wondering if it can be done automatically by the compiler? import scala.collection.JavaConversions._ def convertToJava(listOfMaps: List[Map[String, AnyRef]]): java.util.List[java.util.Map[String, Object]] = { asJavaList(listOfMaps.map(asJavaMap(_))) }

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  • scala jrebel superclass change

    - by coubeatczech
    hi, I'm using JRebel with Scala and I'm quite frequently experiencing the need for restart of server due to the fact that JRebel is unable to load a class if the superclass was changed. This is done mainly when I change anonymous functions as I can deduce from the JRebel error desription: Class 'mypackage.NewBook$$anonfun$2' superclass was changed from 'scala.runtime.AbstractFunction1' to 'scala.runtime.AbstractFunction2' and could not be reloaded. Is there any way, how can I design my code to avoid this? Does scala compiler take the functions, numbers them from one as they appear in source code?

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  • How to deploy a Scala project from Eclipse?

    - by lach
    I have a Scala project in Eclipse that I need to package up so I can deploy it to a server. It's based on Jetty but it runs as a standalone application. It contains Scala classes, Java classes and a number of 3rd party jars. I assumed there would be some kind of deployment option in the Scala Eclipse plugin but I've drawn a blank. What is the simplest way to package the Scala project into a runnable file so it can be deployed? Any help greatly appreciated. Cheers.

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  • Odd behaviour with scala method syntax

    - by Ceilingfish
    Hi chaps, I hit a bit of a quirk of scala's syntax I don't really understand object Board { def getObjectAt(x:Int, y:Int):Placeable = return locations(x)(y) } works fine. But object Board { def getObjectAt(x:Int, y:Int):Placeable { return locations(x)(y) } } returns the error Board.scala:8: error: illegal start of declaration return locations(x)(y) I found some stuff that says the second form convinces the scala compiler you're trying to specify an expansion to the return type Placeable. Is there a way I can fix this, or should I just avoid specifying a return type here?

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  • Generate a sequence of Fibonacci number in Scala

    - by qin
    def fibSeq(n: Int): List[Int] = { var ret = scala.collection.mutable.ListBuffer[Int](1, 2) while (ret(ret.length - 1) < n) { val temp = ret(ret.length - 1) + ret(ret.length - 2) if (temp >= n) { return ret.toList } ret += temp } ret.toList } So the above is my code to generate a Fibonacci sequence using Scala to a value n. I am wondering if there is a more elegant way to do this in Scala?

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  • Scala : cleanest way to recursively parse files checking for multiple strings

    - by fred basset
    Hi All, I want to write a Scala script to recursively process all files in a directory. For each file I'd like to see if there are any cases where a string occurs at line X and line X - 2. If a case like that occurs I'd like to stop processing that file, and add that filename to a map of filenames to occurrence counts. I just started learning Scala today, I've got the file recurse code working, and need some help with the string searching, here's what I have so far: import java.io.File import scala.io.Source val s1= "CmdNum = 506" val s2 = "Data = [0000,]" def processFile(f: File) { val lines = scala.io.Source.fromFile(f).getLines.toArray for (i = 0 to lines.length - 1) { // want to do string searches here, see if line contains s1 and line two lines above also contains s1 //println(lines(i)) } } def recursiveListFiles(f: File): Array[File] = { val these = f.listFiles if (these != null) { for (i = 0 to these.length - 1) { if (these(i).isFile) { processFile(these(i)) } } these ++ these.filter(_.isDirectory).flatMap(recursiveListFiles) } else { Array[File]() } } println(recursiveListFiles(new File(args(0))))

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  • Scala's tuple unwrapping nuance

    - by Paul Milovanov
    I've noticed the following behavior in scala when trying to unwrap tuples into vals: scala> val (A, B, C) = (1, 2, 3) <console>:5: error: not found: value A val (A, B, C) = (1, 2, 3) ^ <console>:5: error: not found: value B val (A, B, C) = (1, 2, 3) ^ <console>:5: error: not found: value C val (A, B, C) = (1, 2, 3) ^ scala> val (u, v, w) = (1, 2, 3) u: Int = 1 v: Int = 2 w: Int = 3 Is that because scala's pattern matching mechanism automatically presumes that all identifiers starting with capitals within patterns are constants, or is that due to some other reason? Thanks!

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  • scala: defining a tratit and referencing the corresponding companion object

    - by opensas
    I'm trying to define a trait that uses the corresponding companion object, that is, the componion object of the class using the trait. for example, I have: :paste class Parent { def callMyCompanion = print(Parent.salute) } object Parent { def salute = "Hello from Parent companion object" } class Child extends Parent { } object Child { def salute = "Hello from Child companion object" } And then I create a parent object: scala> val p = new Parent() p: Parent = Parent@1ecf669 scala> p.callMyCompanion Hello from Parent companion object But with a child: scala> val c = new Child() c: Child = Child@4fd986 scala> c.callMyCompanion Hello from Parent companion object I'd like to get: Hello from Child companion object How can I achieve it???

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  • Bringing Scala into my company

    - by raichoo
    Hi, Now i know that this one is actually not a very technical question but one that has been bothering me for some time. Actually we are using a lot of C++ and PHP at our company and some of our developers are really hoping for a new and modern language to come by to help us getting more productive. I have been talking about what scala can do and the other coders seem to gain some interest in the language. The tough job is, how do you convince your boss to consider scala as a language for the company. I saw the presentation "Sneaking Scala into your company", but it deals with the situation that you are using Java at your company which we don't. How do you fight of the usual "that is just esoteric stuff" and "we can already do that in $LANGUAGE" arguments. I was planing to give a talk about Scala, and since I don't have much time I need Killer Arguments. How did you guys do it? Regards, raichoo

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  • What's the difference between Scala and Red Hat's Ceylon language?

    - by John Bryant
    Red Hat's Ceylon language has some interesting improvements over Java: The overall vision: learn from Java's mistakes, keep the good, ditch the bad The focus on readability and ease of learning/use Static Typing (find errors at compile time, not run time) No “special” types, everything is an object Named and Optional parameters (C# 4.0) Nullable types (C# 2.0) No need for explicit getter/setters until you are ready for them (C# 3.0) Type inference via the "local" keyword (C# 3.0 "var") Sequences (arrays) and their accompanying syntactic sugariness (C# 3.0) Straight-forward implementation of higher-order functions I don't know Scala but have heard it offers some similar advantages over Java. How would Scala compare to Ceylon in this respect?

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  • Scala: is it possible to override default case class constructor?

    - by adam77
    Just wondering if this is possible. What I would actually like to do is check and possibly modify one of the arguments before it is stored as a val. Alternatively, I could use an overload and make the default constructor private. In which case I would also like to make private the default factory constructor in the companion object, how would I do that? Many thanks. Adam

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  • Collection type generated by for with yield

    - by Jesper
    When I evaluate a for in Scala, I get an immutable IndexedSeq (a collection with array-like performance characteristics, such as efficient random access): scala> val s = for (i <- 0 to 9) yield math.random + i s: scala.collection.immutable.IndexedSeq[Double] = Vector(0.6127056766832756, 1.7137598183155291, ... Does a for with a yield always return an IndexedSeq, or can it also return some other type of collection class (a LinearSeq, for example)? If it can also return something else, then what determines the return type, and how can I influence it? I'm using Scala 2.8.0.RC3.

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