Question

Perhaps I am barking up the wrong tree (again) but if it is normal practice to have a property typed as a scala.collection.immutable.Set[A], then how would you create one of these given a scala.Iterable[A]? For example:

class ScalaClass {     private var s: scala.collection.immutable.Set[String]      def init(): Unit = {         val i = new scala.collection.mutable.HashSet[String]          //ADD SOME STUFF TO i          s = scala.collection.immutable.Set(i) //DOESN'T WORK          s = scala.collection.immutable.Set(i toSeq : _ *) //THIS WORKS     } } 

Can someone explain why it is necessary to create the immutable set via a Seq (or if it is not, then how do I do it)?

Answer 1

Basically because you’re creating the immutable Set through the ‘canonical factory method’ apply in Set’s companion object, which takes a sequence, or ‘varargs’ (as in Set(a,b,c)). See this:
http://scala-tools.org/scaladocs/scala-library/2.7.1/scala/collection/immutable/Set$object.html

I don’t think there is another to do it in the standard library.