scala-2.8

Was trying to compile some code from this SO question and run into this error message cannot find class manifest for element type T . Here is another snippet that shows the behavior: scala> def f[T](a:T, b:T):Array[T] = { new Array[T](2) } <console>:4: error: cannot find class manifest for element type T def f[T](a:T, b:T):Array[T] = { new Array[T](2) } I can see that new collection.mutable.GenericArray[T](2) fixes the issue. Apparently providing a manifest is the other option... But what does "providing a manifest mean" ? To provide type information you can use a context bound def f[T :

I have a Set in Scala (I can choose any implementation as I am creating the Set. The Java library I am using is expecting a java.util.Set[String]. Is the following the correct way to do this in Scala (using scala.collection.jcl.HashSet#underlying): import com.javalibrary.Animals var classes = new scala.collection.jcl.HashSet[String] classes += "Amphibian" classes += "Reptile" Animals.find(classes.underlying) It seems to be working, but since I am very new to Scala I want to know if this is the preferred way (any other way I try I am getting a type-mismatch error): error: type mismatch; found :

In many examples, it is described that you can use scala.io.Source to read a whole file like this: val str = scala.io.Source.fromFile("test.txt").mkString() But closing the underlying stream is not mentioned. Why does Scala not provide a convenient way to do that such as with clause in Python? It looks useful but not difficult. Is there any other better way to do that safely in Scala, I means to read a whole file? For the sake of completeness val testTxtSource = scala.io.Source.fromFile("test.txt") val str = testTxtSource.mkString() testTxtSource.close() Should get things done. Daniel C.

I just recently encountered the term "Weak Conformance" (in Stack Overflow user retronym 's answer to How to set up implicit conversion to allow arithmetic between numeric types? ). What is it? 3.5.3 Weak Conformance In some situations Scala uses a more general conformance relation. A type S weakly conforms to a type T , written S <: w T , if S <: T or both S and T are primitive number types and S precedes T in the following ordering. Byte <: w Short Byte <: w Character Short <: w Int Int <: w Long Long <: w Float Float <: w Double A weak least upper bound is a least upper bound with respect

How does scala.collection.JavaConversions supercede the answers given in Stack Overflow question Iterating over Java collections in Scala (it doesn't work because the "jcl" package is gone) and in Iterating over Map with Scala (it doesn't work for me in a complicated test which I'll try to boil down and post here later). The latter is actually a Scala Map question, but I think I need to know both answers in order to iterate over a java.util.Map . In 2.8, you import scala.collection.JavaConversions._ and use as a Scala map. Here's an example (in 2.8.0.RC1): scala> val jmap:java.util.Map[String

Following watching Nick Partidge's presentation on deriving scalaz , I got to looking at this example, which is just awesome: import scalaz._ import Scalaz._ def even(x: Int) : Validation[NonEmptyList[String], Int] = if (x % 2 ==0) x.success else "not even: %d".format(x).wrapNel.fail println( even(3) <|*|> even(5) ) //prints: Failure(NonEmptyList(not even: 3, not even: 5)) I was trying to understand what the <|*|> method was doing, here is the source code: def <|*|>[B](b: M[B])(implicit t: Functor[M], a: Apply[M]): M[(A, B)] = <**>(b, (_: A, _: B)) OK, that is fairly confusing (!) - but it