SI-9913 Tighten bolts on span iterator

Extra privacy, and the tricky state transition is made
more tabular.

1 files changed, 10 insertions, 13 deletions

diff --git a/src/library/scala/collection/Iterator.scala b/src/library/scala/collection/Iterator.scala
index 720339f054..03b9fbff26 100644
--- a/src/library/scala/collection/Iterator.scala
+++ b/src/library/scala/collection/Iterator.scala
@@ -648,15 +648,15 @@ trait Iterator[+A] extends TraversableOnce[A] {
      * handling of structural calls. It's not what's intended here.
      */
     class Leading extends AbstractIterator[A] {
-      var lookahead: mutable.Queue[A] = null
-      var hd: A = _
+      private[this] var lookahead: mutable.Queue[A] = null
+      private[this] var hd: A = _
       /* Status is kept with magic numbers
        *   1 means next element is in hd and we're still reading into this iterator
        *   0 means we're still reading but haven't found a next element
        *   -1 means we are done reading into the iterator, so we must rely on lookahead
        *   -2 means we are done but have saved hd for the other iterator to use as its first element
        */
-      var status = 0
+      private[this] var status = 0
       private def store(a: A) {
         if (lookahead == null) lookahead = new mutable.Queue[A]
         lookahead += a
@@ -680,14 +680,11 @@ trait Iterator[+A] extends TraversableOnce[A] {
         }
         else empty.next()
       }
-      def finish(): Boolean = {
-        if (status == -1) false
-        else if (status == -2) {
-          status = -1
-          true
-        }
-        else {
-          if (status == 1) store(hd)
+      def finish(): Boolean = status match {
+        case -2 => status = -1 ; true
+        case -1 => false
+        case  1 => store(hd) ; status = 0 ; finish()
+        case  0 => 
           status = -1
           while (self.hasNext) {
             val a = self.next()
@@ -698,8 +695,8 @@ trait Iterator[+A] extends TraversableOnce[A] {
             }
           }
           false
-        }
       }
+      def trailer: A = hd
     }
     
     val leading = new Leading
@@ -732,7 +729,7 @@ trait Iterator[+A] extends TraversableOnce[A] {
           if (status > 0) self.next()
           else {
             status = 1
-            val ans = myLeading.hd
+            val ans = myLeading.trailer
             myLeading = null
             ans
           }