Merge pull request #4175 from Ichoran/issue/7981

SI-7981  toSeq on immutable Map and Set return ArrayBuffer

4 files changed, 47 insertions, 6 deletions

diff --git a/src/library/scala/collection/MapLike.scala b/src/library/scala/collection/MapLike.scala
index 3de30c2c8b..38a598321f 100644
--- a/src/library/scala/collection/MapLike.scala
+++ b/src/library/scala/collection/MapLike.scala
@@ -323,11 +323,20 @@ self =>
     res
   }
 
-  /* Overridden for efficiency. */
-  override def toSeq: Seq[(A, B)] = toBuffer[(A, B)]
+  override def toSeq: Seq[(A, B)] = {
+    if (isEmpty) Vector.empty[(A, B)]
+    else {
+      // Default appropriate for immutable collections; mutable collections override this
+      val vb = Vector.newBuilder[(A, B)]
+      foreach(vb += _)
+      vb.result
+    }
+  }  
+  
   override def toBuffer[C >: (A, B)]: mutable.Buffer[C] = {
     val result = new mutable.ArrayBuffer[C](size)
-    copyToBuffer(result)
+    // Faster to let the map iterate itself than to defer through copyToBuffer
+    foreach(result += _)
     result
   }
 
diff --git a/src/library/scala/collection/SetLike.scala b/src/library/scala/collection/SetLike.scala
index 3e549f72cd..80a344e6a8 100644
--- a/src/library/scala/collection/SetLike.scala
+++ b/src/library/scala/collection/SetLike.scala
@@ -77,11 +77,20 @@ self =>
 
   protected[this] override def parCombiner = ParSet.newCombiner[A]
 
-  /* Overridden for efficiency. */
-  override def toSeq: Seq[A] = toBuffer[A]
+  // Default collection type appropriate for immutable collections; mutable collections override this
+  override def toSeq: Seq[A] = {
+    if (isEmpty) Vector.empty[A]
+    else {
+      val vb = Vector.newBuilder[A]
+      foreach(vb += _)
+      vb.result
+    }
+  }
+  
   override def toBuffer[A1 >: A]: mutable.Buffer[A1] = {
     val result = new mutable.ArrayBuffer[A1](size)
-    copyToBuffer(result)
+    // Faster to let the map iterate itself than to defer through copyToBuffer
+    foreach(result += _)
     result
   }
 
diff --git a/src/library/scala/collection/mutable/MapLike.scala b/src/library/scala/collection/mutable/MapLike.scala
index 6230fc23aa..8ba31d47b6 100644
--- a/src/library/scala/collection/mutable/MapLike.scala
+++ b/src/library/scala/collection/mutable/MapLike.scala
@@ -59,6 +59,18 @@ trait MapLike[A, B, +This <: MapLike[A, B, This] with Map[A, B]]
   override protected[this] def newBuilder: Builder[(A, B), This] = empty
 
   protected[this] override def parCombiner = ParMap.newCombiner[A, B]
+  
+  /** Converts this $coll to a sequence.
+    *
+    * ```Note```: assumes a fast `size` method.  Subclasses should override if this is not true.
+    */
+  override def toSeq: collection.Seq[(A, B)] = {
+    // ArrayBuffer for efficiency, preallocated to the right size.
+    val result = new ArrayBuffer[(A, B)](size)
+    foreach(result += _)
+    result
+  }
+
 
   /** Adds a new key/value pair to this map and optionally returns previously bound value.
    *  If the map already contains a
diff --git a/src/library/scala/collection/mutable/SetLike.scala b/src/library/scala/collection/mutable/SetLike.scala
index a377b03124..cbe7a639dd 100644
--- a/src/library/scala/collection/mutable/SetLike.scala
+++ b/src/library/scala/collection/mutable/SetLike.scala
@@ -72,6 +72,17 @@ trait SetLike[A, +This <: SetLike[A, This] with Set[A]]
 
   protected[this] override def parCombiner = ParSet.newCombiner[A]
 
+  /** Converts this $coll to a sequence.
+    *
+    * ```Note```: assumes a fast `size` method.  Subclasses should override if this is not true.
+    */
+  override def toSeq: collection.Seq[A] = {
+    // ArrayBuffer for efficiency, preallocated to the right size.
+    val result = new ArrayBuffer[A](size)
+    foreach(result += _)
+    result
+  }
+
   /** Adds an element to this $coll.
    *
    *  @param elem the element to be added