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    Be careful that vals is a strict collection -- if it's lazy (and in Scala 2.7 this includes the Range class), the futures won't be created until each one is needed by foreach, and nothing will happen in parallel.
    – Ken Bloom
    Commented Nov 18, 2009 at 5:34
  • I suppose we could solve that problem by injecting another foreach call between the map and the current foreach. Thus: vals map { x => future { f(x) } } foreach { x => x } foreach { _() }
    – Daniel Spiewak
    Commented Nov 18, 2009 at 15:43
  • That would be a map we have to inject, not another foreach? And it is not clear to me that the map of a lazy collection is strict. The safest way may be to call toArray.
    – David Crawshaw
    Commented Nov 20, 2009 at 22:50
  • You're right, foreach was (obviously) the wrong thing to inject since it returns Unit. My bad! :-) The map function on lazy collections is almost always non-strict, so we can either call toList (or toArray), or we can project and then force: (vals map { x => future { f(x) } } projection).force foreach { _() }. I don't know whether that's better than simply toList, but it is certainly different.
    – Daniel Spiewak
    Commented Nov 22, 2009 at 2:01
  • What does it mean when you say it "returns asynchronously"? Does it imply that it is non-blocking? (and why would that be a problem?)
    – Jus12
    Commented Aug 5, 2014 at 14:24