fixup! adds groupUntilChanged extension method on scala.collection.Iterator

Author: jeantil

src/main/scala/scala/collection/decorators/IteratorDecorator.scala

@@ -95,21 +95,39 @@ class IteratorDecorator[A](val `this`: Iterator[A]) extends AnyVal {
     */
   def splitBy[K](f: A => K): Iterator[Iterable[A]] =
     new AbstractIterator[Seq[A]] {
-      private var hd: Option[A] = `this`.nextOption()
-      override def hasNext: Boolean = hd.isDefined
-
+      private var hd: A = _
+      private var hdDefined: Boolean = false
+      
+      override def hasNext: Boolean = hdDefined || `this`.hasNext
+      
       override def next(): Seq[A] = {
-        hd match {
-          case None => Iterator.empty.next()
-          case Some(head) =>
-            hd = `this`.nextOption()
-            var seq = mutable.Buffer(head)
-            while (hd.exists(el => f(el) == f(head))) {
-              seq = seq ++ hd
-              hd = `this`.nextOption()
+        if(hasNext) {
+          val seq = Vector.newBuilder[A]
+          if(hdDefined) {
+            seq += hd
+          } else {
+            hd = `this`.next()
+            hdDefined = true
+            seq += hd
+          }
+          var hadSameKey = true
+          while(`this`.hasNext && hadSameKey)  {
+            val el = `this`.next()
+            hdDefined = true
+            if(f(el) == f(hd)) {
+              seq += el              
+            }else{
+              hadSameKey=false
             }
-            seq.toVector
+            hd = el
+          }
+          if(hadSameKey) {
+            hdDefined = false
+          }    
+          seq.result()
+        }else{
+          Iterator.empty.next()
         }
-      }
+      }     
     }
 }