Questions tagged [scala-2.9]
Version 2.9 of the Scala language for the JVM.
scala-2.9
102
questions
179
votes
17
answers
155k
views
Scala: write string to file in one statement
For reading files in Scala, there is
Source.fromFile("file.txt").mkString
Is there an equivalent and concise way to write a string to file?
Most languages support something like that. My favorite ...
- 6,394
52
votes
1
answer
24k
views
What is the === (triple-equals) operator in Scala Koans?
I started working my way through the Scala Koans, which is organized around a suite of unit tests with blanks that one needs to fill in. (This idea was modeled after a similar Ruby Koans project.) ...
- 3,167
37
votes
4
answers
6k
views
Is there a way to declare an implicit val inside a for comprehension?
I have some code with nested calls to flatMap like so:
foo.flatMap(implicit f => bar(123).flatMap(b =>
/* and so on... implicit f is still in scope here.*/
))
Normally, one would write that ...
- 42k
29
votes
4
answers
12k
views
SBT including the version number in a program
I want a program I'm building to be able to report its own version at runtime (e.g. scala myprog.jar --version). Traditionally in a maven project, I'd use resource filtering (pom.xml -> file....
- 48.3k
21
votes
9
answers
40k
views
coin change algorithm in scala using recursion
I am trying to program the coin change problem in Scala using recursion. The code that i have written is as follows.
def countChange(money: Int, coins: List[Int]): Int = {
def ways(change: List[Int]...
- 408
20
votes
7
answers
5k
views
How can I fix the missing implicit value for parameter ta: TildeArrow in a test spec
I'm working on a simple test spec using spray and I can't get it to compile correctly, don't know if I'm doing anything wrong. My version of scala is 2.9.3 and spray 1.0.1 (Updating either of them is ...
- 218
19
votes
2
answers
2k
views
How do I replace the fork join pool for a Scala 2.9 parallel collection?
I've been looking at the new Scala 2.9 parallel collections and am hoping to abandon a whole lot of my crufty amateur versions of similar things. In particular, I'd like to replace the fork join pool ...
- 3,145
18
votes
2
answers
7k
views
Add tools.jar in the classpath of sbt project
The ':javap' command in the scala 2.9.1 console need the tools.jar (from JDK6) in the 'classpath'. From cmd-line it could be done with '-cp' argument or CLASSPATH environment variable.
How to do the ...
- 203
18
votes
4
answers
3k
views
What new features will be added to Scala 2.9?
I know parallel collections will become available.
What form will these take, and what else are we likely to see?
- 49.6k
15
votes
3
answers
2k
views
Why do case classes extend only Product and not Product1, Product2, ..., ProductN?
after I learned that case classes extend Product, I wondered why they do not extend ProductN. E.g., given a code like:
case class Foo(a: Int)
I'd expect Foo(1).asInstanceOf[Product1[Int]] to work, ...
- 6,468
15
votes
1
answer
3k
views
How can I best troubleshoot "Potentially incompatible versions of dependencies" in sbt
My project gives the following warning:
[warn] Potentially incompatible versions of dependencies of {file:/some/path/}default-5bae4a:
[warn] org.scala-lang: 2.9.2, 2.9.1
I've got the following ...
- 26k
14
votes
3
answers
1k
views
Scala Parallel Collections- How to return early?
I have a list of possible input Values
val inputValues = List(1,2,3,4,5)
I have a really long to compute function that gives me a result
def reallyLongFunction( input: Int ) : Option[String] = { ......
- 15k
11
votes
2
answers
2k
views
Parallel collections in Scala 2.9 and Actors
Ok, this might be a rather silly question, but what is the benefit of using parallel collections within an actor framework? That is, if I'm only dealing with one message at a time from an actor's ...
- 1,861
10
votes
2
answers
2k
views
How do you make a list with 100 1s in Scala 2.9
In earlier versions of Scala you can use List.make(100, 1), but that is now deprecated. What is the new proper way to do it?
- 2,166
10
votes
1
answer
1k
views
What is Scala REPL's tab completion telling me here?
While working my way through Cay S. Horstmann's "Scala for the Impatient", I noticed something interesting revealed by the first exercise in the first chapter.
In the Scala REPL, type 3. followed by ...
- 3,167
9
votes
2
answers
17k
views
Getting started with Scala, Scalatest, and Maven
I created a new scala project with the following:
mvn org.apache.maven.plugins:maven-archetype-plugin:2.2:generate
-DarchetypeGroupId=org.scala-tools.archetypes
-DarchetypeArtifactId=scala-...
- 2,137
9
votes
1
answer
523
views
Strange behavior of Set4 in scala 2.9.1?
Making a migration from 2.8.1 to 2.9.1 found interesting thing.
Tried to write this in console:
>>import collection.immutable.Set.Set4
>>new Set4[Int](1,2,3,4)
It gives:
java.lang.Error:...
- 1,489
8
votes
1
answer
5k
views
How can I sort List[Int] objects?
What I want to do is sort List objects in Scala, not sort the elements in the list. For example If I have two lists of Ints:
val l1 = List(1, 2, 3, 7)
val l2 = List(1, 2, 3, 4, 10)
I want to be able ...
- 319
8
votes
1
answer
3k
views
Reference a constructor argument from a trait
In Scala, is it possible for a trait to reference a named constructor argument of the class it is mixed into? The code below doesn't compile because ModuleDao's constructor argument is not a val as ...
- 11.5k
8
votes
3
answers
534
views
Case classes and Proxy behaviour in Scala 2.9
On migrating our code to Scala 2.9 we've found large swathes of it that didn't work and failed silently. We tracked it down to case classes that extend Proxy not being equal. In our code we don't ...
- 1,914
7
votes
3
answers
4k
views
converting Akka's Future[A] to Future[Either[Exception,A]]
Is there a method in Akka (or in the standard library in Scala 2.10) to convert a Future[A] which might fail into a Future[Either[Exception,A]]? I know that you can write
f.map(Right(_)).recover {
...
- 42k
7
votes
1
answer
405
views
Why doesn't scala's parallel sequences have a contains method?
Why does
List.range(0,100).contains(2)
Work, while
List.range(0,100).par.contains(2)
Does not?
This is planned for the future?
- 2,166
7
votes
2
answers
17k
views
Constructor cannot be instantiated to expected type; p @ Person
I am using scala version : Scala code runner version 2.9.2-unknown-unknown -- Copyright 2002-2011, LAMP/EPFL
I was trying the deep case matching construct from here: http://ofps.oreilly.com/titles/...
- 8,377
7
votes
2
answers
4k
views
What is the fastest way to subtract two arrays in scala
I have two arrays (that i have pulled out of a matrix (Array[Array[Int]]) and I need to subtract one from the other.
At the moment I am using this method however, when I profile it, it is the ...
- 319
7
votes
1
answer
1k
views
Why is this not faster using parallel collections?
I just wanted to test the parallel collections a bit and I used the following line of code (in REPL):
(1 to 100000).par.filter(BigInt(_).isProbablePrime(100))
against:
(1 to 100000).filter(BigInt(_)...
- 843
7
votes
1
answer
2k
views
How should one start on creating a sbt plugin?
I want to create a sbt plugin for Scala project.
Please any one suggest me how we start?
I referred Plugins documentation but unable to understand steps.
7
votes
1
answer
729
views
What are main changes from scala 2.8.1 to scala 2.9.1?
I am working on project implemented in scala 2.8.1, want to migrate to scala 2.9.1 and use akka-actors libraries instead of standard, but didn't find good summary of main changes, here what I found:
...
- 1,489
7
votes
1
answer
3k
views
How to convert scala.collection.Set to java.util.Set with serializable within an RDD
I have a scala.collection.Set scalaSet : Set[Long].
How will I be able to convert it into a java.util.Set with serializable. I tried the following code, but got
java.io.notserializableexception: ...
- 95
7
votes
3
answers
1k
views
Modifying a large file in Scala
I am trying to modify a large PostScript file in Scala (some are as large as 1GB in size). The file is a group of batches, with each batch containing a code that represents the batch number, number of ...
- 1,436
7
votes
1
answer
1k
views
How does one implement a Hadoop Mapper in Scala 2.9.0?
When I migrated to Scala 2.9.0 from 2.8.1, all of the code was functional except for the Hadoop mappers. Because I had some wrapper objects in the way, I distilled down to the following example:
...
- 71
7
votes
1
answer
810
views
In which case can Scala 2.10.0 compiler be faster or slower than 2.9.2?
I did a benchmark for compilation time on Scala 2.10.0 and 2.9.2, and have found that 2.10.0 took longer compilation time than 2.9.2.
In which case does it happen? Or can Scala 2.10.0 compiler be ...
- 3,108
6
votes
2
answers
4k
views
Scala List Comprehensions
I'm trying to generate a list in scala according to the formula:
for n > 1 f(n) = 4*n^2 - 6*n + 6 and for n == 1 f(n) = 1
currently I have:
def lGen(end: Int): List[Int] = {
for { n <- ...
- 275
6
votes
3
answers
615
views
Dynamic Proxy using Scalas new Dynamic Type
Is it possible to create an AOP like interceptor using Scalas new Dynamic Type feature? For example: Would it be possible to create a generic stopwatch interceptor that could be mixed in with ...
- 1,686
6
votes
1
answer
610
views
Array[Nothing with java.lang.Object] required in Scala 2.9.1
I have a weird compilation error. The offending lines are:
val comboBoxLanguage = new javax.swing.JComboBox
//...
comboBoxLanguage.setModel(new javax.swing.DefaultComboBoxModel(
Array[Object]("...
- 50.9k
6
votes
2
answers
1k
views
Step by step guide to get Scala to run on .net?
I have never used .Net framework and need to demonstrate to someone that Scala indeed works on .Net. I need to get a "quick and dirty" .Net setup with Scala working on some existing JVM Scala code. I ...
- 18k
6
votes
3
answers
209
views
Generic collect by type in scala
In Scala 2.9.1
With
def collectFirstOfT[T](la: List[_])(implicit m:Manifest[T]) : Option[T] = {
la.collect{case x if m.erasure.isAssignableFrom(x.getClass) => x}.
headOption.asInstanceOf[...
- 1,749
6
votes
3
answers
491
views
Using ListView from Scala 2.9.2 with Java 7 gives compile error
I'm working on a project that use scala 2.9.2 and java 7.
What I'm trying to do is create a GUI using the scala ListView.
Here's a small code snippet:
private val listView = new ListView[Document](...
- 641
6
votes
1
answer
695
views
Scala 2.9 Bridge-Method
I'm using Scala 2.9.1
I've defined a Logging trait as such:
trait Logging {
def debug(msg: String, throwables: Throwable*) = ....
....
}
And I have a JMSPublisher class which mixes-in the ...
- 1,628
6
votes
1
answer
792
views
Is this a bug in scala 2.9.0.1 actor library
The following code works fine in Scala 2.8 but not in 2.9.0.1
(copy and paste in REPL). This will throw an exception in 2.9.0.1.
import scala.actors.Actor
import scala.actors.TIMEOUT
object A2 ...
- 18k
5
votes
3
answers
8k
views
How can I use Scala's MurmurHash implementation: scala.util.MurmurHash3?
I'm writing a BloomFilter and wanted to use Scala's default MurmurHash3 implementation: scala.util.MurmurHash3. My compile is failing however with the following compile error:
[error] /mnt/hgfs/dr/...
- 247
5
votes
1
answer
617
views
How do I use nightly builds of Scala 2.9 with maven?
Recently I wanted to try some of the new features in Scala 2.9 in a small project. I would like to use maven for building it. How can I tell Maven to use the latest nightly build of Scala 2.9? If ...
- 42k
5
votes
1
answer
323
views
How can I override a method with a dependent return type?
I'm having trouble in Scala 2.9.2 implementing a method which declares a dependent return type. The following code
object DependentTypesQuestion {
def ??? = throw new UnsupportedOperationException
...
- 3,145
5
votes
1
answer
410
views
Why does Scala define a "+=" operator for Short and Byte types?
Given the following scala code:
var short: Short = 0
short += 1 // error: type mismatch
short += short // error: type mismatch
short += 1.toByte // error: type mismatch
I don't questioning ...
- 8,372
5
votes
0
answers
1k
views
What IDEs support SBT and Scala version 2.9.0 [duplicate]
Possible Duplicate:
Which IDE for Scala 2.8?
I would like to know which IDEs specifically support Scala 2.9 and the sbt project ?
- 347
4
votes
1
answer
4k
views
counting down in scala for loop [duplicate]
Possible Duplicate:
Decreasing for loop in Scala?
While working through [Scala For The Impatient][1], I came upon the following exercise:
Write a Scala equivalent for the Java loop
for (int i ...
- 3,167
4
votes
1
answer
3k
views
How to import class using fully qualified name?
create file test1.scala with following code:
package test
import java.io.FileInputStream
object Foo
create another file test2.scala with following code:
package test.java
object Bar
Now compile ...
- 18k
4
votes
3
answers
2k
views
Scala: Generic class with multiple constructors
I'm trying to create a generic class like this:
class A[T](v: Option[T]) {
def this(v: T) = this(Some(v))
def this() = this(None)
def getV = v
}
Then I do some testing:
scala> new A getV
...
- 3,738
4
votes
3
answers
2k
views
Scala 2.10 vs. 2.9 incompatibilities [closed]
What are the Scala 2.10 vs. 2.9 incompatibilities and how to deal with them?
Especially core libraries, but any issues with popular libraries might be interesting.
Links to official documents are ...
- 1,977
4
votes
1
answer
231
views
Methods in trait become volatile methods when mixed in concrete classes in 2.9.0-1 but not 2.8.1
I noticed this breaking (for me using it with OGNL) change in 2.9.0-1:
I find that, in 2.9, methods declared in a trait become volatile when mixed in a class:
Example in 2.9.0-1
import java.lang....
- 912
4
votes
1
answer
163
views
Why does 2.10 insist on specifying type parameter bounds (worked fine in 2.9)?
I have the following case class:
case class Alert[T <: Transport](destination: Destination[T], message: Message[T])
In Scala 2.9.2, the following method signature has compiled fine:
def send(...
- 21.9k