Merge pull request scala/scala#8957 from mkeskells/2.12.x_SortedSet_SortedMap

Author: lrytz

library/src/scala/collection/generic/SortedMapFactory.scala

@@ -27,7 +27,10 @@ abstract class SortedMapFactory[CC[A, B] <: SortedMap[A, B] with SortedMapLike[A
 
   def empty[A, B](implicit ord: Ordering[A]): CC[A, B]
 
-  def apply[A, B](elems: (A, B)*)(implicit ord: Ordering[A]): CC[A, B] = (newBuilder[A, B](ord) ++= elems).result()
+  def apply[A, B](elems: (A, B)*)(implicit ord: Ordering[A]): CC[A, B] = {
+    if (elems.isEmpty) empty
+    else (newBuilder[A, B](ord) ++= elems).result()
+  }
 
   def newBuilder[A, B](implicit ord: Ordering[A]): Builder[(A, B), CC[A, B]] =
     new MapBuilder[A, B, CC[A, B]](empty(ord))

library/src/scala/collection/generic/SortedSetFactory.scala

@@ -26,7 +26,10 @@ abstract class SortedSetFactory[CC[A] <: SortedSet[A] with SortedSetLike[A, CC[A
 
   def empty[A](implicit ord: Ordering[A]): CC[A]
 
-  def apply[A](elems: A*)(implicit ord: Ordering[A]): CC[A] = (newBuilder[A](ord) ++= elems).result()
+  def apply[A](elems: A*)(implicit ord: Ordering[A]): CC[A] = {
+    if (elems isEmpty) empty
+    else (newBuilder[A](ord) ++= elems).result()
+  }
 
   def newBuilder[A](implicit ord: Ordering[A]): Builder[A, CC[A]] = new SetBuilder[A, CC[A]](empty)
 

library/src/scala/collection/immutable/SortedMap.scala

@@ -127,6 +127,8 @@ object SortedMap extends ImmutableSortedMapFactory[SortedMap] {
   implicit def canBuildFrom[A, B](implicit ord: Ordering[A]): CanBuildFrom[Coll, (A, B), SortedMap[A, B]] = new SortedMapCanBuildFrom[A, B]
   def empty[A, B](implicit ord: Ordering[A]): SortedMap[A, B] = TreeMap.empty[A, B]
 
+  override def newBuilder[A, B](implicit ord: Ordering[A]): mutable.Builder[(A, B), SortedMap[A, B]] = TreeMap.newBuilder[A, B]
+
   private[collection] trait Default[A, +B] extends SortedMap[A, B] with scala.collection.SortedMap.Default[A, B] {
   self =>
     override def +[B1 >: B](kv: (A, B1)): SortedMap[A, B1] = {

library/src/scala/collection/immutable/SortedSet.scala

@@ -53,6 +53,9 @@ object SortedSet extends ImmutableSortedSetFactory[SortedSet] {
   /** $sortedSetCanBuildFromInfo */
   def canBuildFrom[A](implicit ord: Ordering[A]): CanBuildFrom[Coll, A, SortedSet[A]] = newCanBuildFrom[A]
   def empty[A](implicit ord: Ordering[A]): SortedSet[A] = TreeSet.empty[A]
+
+  override def newBuilder[A](implicit ord: Ordering[A]): mutable.Builder[A, SortedSet[A]] = TreeSet.newBuilder[A]
+
   // Force a declaration here so that BitSet (which does not inherit from SortedSetFactory) can be more specific
   override implicit def newCanBuildFrom[A](implicit ord : Ordering[A]) : CanBuildFrom[Coll, A, SortedSet[A]] = super.newCanBuildFrom
 }