scala-2.8

In trying to write an API I'm struggling with Scala's collections in 2.8(.0-beta1). Basically what I need is to write something that: adds functionality to immutable sets of a certain type where all methods like filter and map return a collection of the same type without having to override everything (which is why I went for 2.8 in the first place) where all collections you gain through those methods are constructed with the same parameters the original collection had (similar to how SortedSet hands through an ordering via implicits) which is still a trait in itself, independent of any set

I would like to construct my domain model using immutable objects only. But I also want to use traits with val fields and move some functionality to traits. Please look at the following example: trait Versionable { val version = 0 def incrementVersion = copy(version=version+1) } Unfortunatelly such code doesn't work - copy method is unknown for trait Versionable. I think that it would be nice to have copy method generated for every trait and class. Such method should create shallow copy of object and return it using the same type as for original object with given field modified accoring to

My problem is very simple but I haven't found an efficient implementation yet. Suppose there is a matrix A like this: 0 0 0 0 0 0 0 4 4 2 2 2 0 0 4 4 2 2 2 0 0 0 0 2 2 2 1 1 0 0 0 0 0 1 1 Now I want to find all starting positions of rectangular areas in this matrix which have a given size. An area is a subset of A where all numbers are the same. Let's say width=2 and height=3. There are 3 areas which have this size: 2 2 2 2 0 0 2 2 2 2 0 0 2 2 2 2 0 0 The result of the function call would be a list of starting positions (x,y starting with 0) of those areas. List((2,1),(3,1),(5,0)) The

I'm probably doing something stupid, but I can't spot it. I've installed Eclipse Helios (Helios because I couldn't get Glassfish support to work correctly using Gallileo) and the nightly build of the Scala Eclipse plugin for Helios I've created a Scala project and added some files - a mix of Java and Scala. They all seem syntactically correct - the Eclipse editor at least seems to know what language each file is, and reports correctly on syntax errors when I make them - but the Java files cannot find classes created in Scala. The IDE site seems to suggest this should all just work. There are

Is there a method to do the following without doing both methods: find and map ? val l = 0 to 3 l.find(_ * 33 % 2 == 0).map(_ * 33) // returns Some(66) Wilfred Springer How about using collect? // Returns List(66) List(1, 2, 3) collect { case i if (i * 33 % 2 == 0) => i * 33 } However that will return all matches and not just the first one. The better answer would have been, based on Scala 2.9: // Returns Some(66) List(1, 2, 3) collectFirst { case i if (i * 33 % 2 == 0) => i * 33 } The solution suggested in the comments to append a head to get a Scala 2.8 version of that is not very efficient,

I have reached this far: implicit def collectionExtras[A](xs: Iterable[A]) = new { def zipWith[B, C, That](ys: Iterable[B])(f: (A, B) => C)(implicit cbf: CanBuildFrom[Iterable[A], C, That]) = { val builder = cbf(xs.repr) val (i, j) = (xs.iterator, ys.iterator) while(i.hasNext && j.hasNext) { builder += f(i.next, j.next) } builder.result } } // collectionExtras: [A](xs: Iterable[A])java.lang.Object{def zipWith[B,C,That](ys: Iterable[B])(f: (A, B) => C)(implicit cbf: scala.collection.generic.CanBuildFrom[Iterable[A],C,That]): That} Vector(2, 2, 2).zipWith(Vector(4, 4, 4))(_ * _) // res3: