diff options
4 files changed, 15 insertions, 7 deletions
diff --git a/src/library/scala/collection/generic/GenericCompanion.scala b/src/library/scala/collection/generic/GenericCompanion.scala index cfcd2a94cf..2d2111f76d 100644 --- a/src/library/scala/collection/generic/GenericCompanion.scala +++ b/src/library/scala/collection/generic/GenericCompanion.scala @@ -43,9 +43,11 @@ abstract class GenericCompanion[+CC[X] <: Traversable[X]] { * @return a new $coll with elements `elems` */ def apply[A](elems: A*): CC[A] = { - val b = newBuilder[A] - b ++= elems - b.result + if (elems.isEmpty) empty[A] + else { + val b = newBuilder[A] + b ++= elems + b.result + } } } - diff --git a/src/library/scala/collection/immutable/ListMap.scala b/src/library/scala/collection/immutable/ListMap.scala index 5fced699f3..9ce5410546 100644 --- a/src/library/scala/collection/immutable/ListMap.scala +++ b/src/library/scala/collection/immutable/ListMap.scala @@ -23,7 +23,9 @@ object ListMap extends ImmutableMapFactory[ListMap] { /** $mapCanBuildFromInfo */ implicit def canBuildFrom[A, B]: CanBuildFrom[Coll, (A, B), ListMap[A, B]] = new MapCanBuildFrom[A, B] - def empty[A, B]: ListMap[A, B] = new ListMap + def empty[A, B]: ListMap[A, B] = EmptyListMap.asInstanceOf[ListMap[A, B]] + + private object EmptyListMap extends ListMap[Any, Nothing] { } } /** This class implements immutable maps using a list-based data structure. diff --git a/src/library/scala/collection/immutable/ListSet.scala b/src/library/scala/collection/immutable/ListSet.scala index 8547ba195b..ec0f2ff5a1 100644 --- a/src/library/scala/collection/immutable/ListSet.scala +++ b/src/library/scala/collection/immutable/ListSet.scala @@ -23,9 +23,11 @@ import mutable.{ ListBuffer, Builder } object ListSet extends ImmutableSetFactory[ListSet] { /** setCanBuildFromInfo */ implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, ListSet[A]] = setCanBuildFrom[A] - override def empty[A] = new ListSet[A] + override def empty[A] = EmptyListSet.asInstanceOf[ListSet[A]] override def newBuilder[A]: Builder[A, ListSet[A]] = new ListSetBuilder[A] + private object EmptyListSet extends ListSet[Any] { } + /** A custom builder because forgetfully adding elements one at * a time to a list backed set puts the "squared" in N^2. There is a * temporary space cost, but it's improbable a list backed set could diff --git a/src/library/scala/collection/immutable/Queue.scala b/src/library/scala/collection/immutable/Queue.scala index bd2f27e57e..3e0181f1a4 100644 --- a/src/library/scala/collection/immutable/Queue.scala +++ b/src/library/scala/collection/immutable/Queue.scala @@ -146,9 +146,11 @@ object Queue extends SeqFactory[Queue] { /** $genericCanBuildFromInfo */ implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, Queue[A]] = new GenericCanBuildFrom[A] def newBuilder[A]: Builder[A, Queue[A]] = new ListBuffer[A] mapResult (x => new Queue[A](Nil, x.toList)) - override def empty[A]: Queue[A] = new Queue[A](Nil, Nil) + override def empty[A]: Queue[A] = EmptyQueue.asInstanceOf[Queue[A]] override def apply[A](xs: A*): Queue[A] = new Queue[A](Nil, xs.toList) + private object EmptyQueue extends Queue[Nothing](Nil, Nil) { } + @deprecated("Use Queue.empty instead") val Empty: Queue[Nothing] = Queue() } |