Convert Seq or List to collection.immutable.Queue

Question

I wonder, if there is a standard and short way to convert Sequence to immutable Queue in Scala?

I did not find a magic method in documentation.

Right now I'm doing it like this:

def toQueue[A](s: Seq[A]): Queue[A] = s match {
  case x +: xs => x +: toQueue(xs)
  case _ => Queue.empty[A]
}

But is there anything more convenient?

score 20 · Accepted Answer · answered Mar 20 '14 at 11:22

20

Why not use s: _*?

val s = List(1, 2, 3) // or Seq(1, 2, 3), as you wish
val queue = scala.collection.immutable.Queue(s: _*)

answered Mar 20 '14 at 11:22

serejja

Cool, it works! Can you please explain or give a link to how `s: _*` syntax works? First time I see that. – Viacheslav Rodionov Mar 20 '14 at 11:27
1

Sure, here you are: http://stackoverflow.com/questions/6051302/what-does-colon-underscore-star-do-in-scala – serejja Mar 20 '14 at 11:27

Xavier Guihot · Answer 2 · 2019-06-30T09:35:40.193

4

Starting Scala 2.13, via factory builders applied with .to(factory):

List(1, 2, 3).to(collection.immutable.Queue)
// collection.immutable.Queue[Int] = Queue(1, 2, 3)

Prior to Scala 2.13 and starting Scala 2.10:

List(1, 2, 3).to[collection.immutable.Queue]
// collection.immutable.Queue[Int] = Queue(1, 2, 3)

edited Jun 30 '19 at 09:35

answered Jun 30 '19 at 09:18

Xavier Guihot

score 1 · Answer 3 · answered Jun 28 '16 at 06:41

1

var s=new scala.collection.mutable.Queue[Any];
var li:List[Any]=List(1,'a',"bing",4,7,9,'j');
for(i<-0 to li.length-1)
{
    s.+=(li(i))
}

answered Jun 28 '16 at 06:41

Guru

3 Answers3