SI-8059 Override immutable.Queue#{+:,:+} for performance

Without those overrides, all elements are unnecessarily copied.

1 files changed, 11 insertions, 1 deletions

diff --git a/src/library/scala/collection/immutable/Queue.scala b/src/library/scala/collection/immutable/Queue.scala
index df1484c4ab..264304db68 100644
--- a/src/library/scala/collection/immutable/Queue.scala
+++ b/src/library/scala/collection/immutable/Queue.scala
@@ -89,6 +89,16 @@ class Queue[+A] protected(protected val in: List[A], protected val out: List[A])
    */
   override def length = in.length + out.length
 
+  override def +:[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Queue[A], B, That]): That = bf match {
+    case _: Queue.GenericCanBuildFrom[_] => new Queue(in, elem :: out).asInstanceOf[That]
+    case _                               => super.+:(elem)(bf)
+  }
+
+  override def :+[B >: A, That](elem: B)(implicit bf: CanBuildFrom[Queue[A], B, That]): That = bf match {
+    case _: Queue.GenericCanBuildFrom[_] => enqueue(elem).asInstanceOf[That]
+    case _                               => super.:+(elem)(bf)
+  }
+
   /** Creates a new queue with element added at the end
    *  of the old queue.
    *
@@ -118,7 +128,7 @@ class Queue[+A] protected(protected val in: List[A], protected val out: List[A])
     case x :: xs            => (x, new Queue(in, xs))
     case _                  => throw new NoSuchElementException("dequeue on empty queue")
   }
-  
+
   /** Optionally retrieves the first element and a queue of the remaining elements.
    *
    * @return A tuple of the first element of the queue, and a new queue with this element removed.