Creating a Queue in Scala

I am trying to create a Queue in Scala by doing:

import scala.collection.immutable.Queue

val empty = new Queue[Int]

However I am getting an error stating that the Queue constructor is protected. If this is the case, am I missing something? All the Queue methods seem to be defined开发者_开发百科 and working. Must I really extend the Queue class for no reason just to use a Queue?

For empty Queue use companion object:

val empty = Queue.empty[Int]

Use one of the factories:

scala.collection.immutable.Queue()
scala.collection.immutable.Queue.empty

Note that immutable queues are co-variant, so you usually don't need to define a type for it. One exception would be var declarations.

scala> val empty = Queue [Int]()
empty: scala.collection.immutable.Queue[Int] = Queue()