Restore lazy iterator.drop

Fix incorrect internal usage of drop. Simplify reverse view iterator slice.
scala · Nov 2, 2021 · 978a527 · 978a527
1 parent 5035461
commit 978a527
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Showing 2 changed files with 15 additions and 27 deletions.
diff --git a/src/library/scala/collection/IndexedSeqView.scala b/src/library/scala/collection/IndexedSeqView.scala
@@ -84,8 +84,8 @@ object IndexedSeqView {
   }
   @SerialVersionUID(3L)
   private[collection] class IndexedSeqViewReverseIterator[A](self: IndexedSeqView[A]) extends AbstractIterator[A] with Serializable {
-    private[this] var pos = self.length - 1
     private[this] var remainder = self.length
+    private[this] var pos = remainder - 1
     @inline private[this] def _hasNext: Boolean = remainder > 0
     def hasNext: Boolean = _hasNext
     def next(): A =
@@ -96,22 +96,17 @@ object IndexedSeqView {
         r
       } else Iterator.empty.next()
 
-    override def drop(n: Int): Iterator[A] = {
-      if (n > 0) {
-        pos -= n
-        remainder = Math.max(0, remainder - n)
-      }
-      this
-    }
-
-    override def sliceIterator(from: Int, until: Int): Iterator[A] = {
+    override protected def sliceIterator(from: Int, until: Int): Iterator[A] = {
       if (_hasNext) {
-        val startCutoff = pos
-        val untilCutoff = startCutoff - remainder + 1
-        val nextStartCutoff = if (from < 0) startCutoff else if (startCutoff - from < 0) 0 else startCutoff - from
-        val nextUntilCutoff = if (until < 0) startCutoff else if (startCutoff - until < untilCutoff) untilCutoff else startCutoff - until + 1
-        remainder = Math.max(0, nextStartCutoff - nextUntilCutoff + 1)
-        pos = nextStartCutoff
+        if (remainder <= from) remainder = 0
+        else if (from <= 0) {
+          if (until >= 0 && until < remainder) remainder = until
+        }
+        else {
+          pos = pos - from
+          if (until >= 0 && until < remainder) remainder = until - from
+          else remainder -= from
+        }
       }
       this
     }

diff --git a/src/library/scala/collection/Iterator.scala b/src/library/scala/collection/Iterator.scala
@@ -409,9 +409,9 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
 
   def indexWhere(p: A => Boolean, from: Int = 0): Int = {
     var i = math.max(from, 0)
-    drop(from)
-    while (hasNext) {
-      if (p(next())) return i
+    val dropped = drop(from)
+    while (dropped.hasNext) {
+      if (p(dropped.next())) return i
       i += 1
     }
     -1
@@ -635,14 +635,7 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
     def next() = if (hasNext) { hdDefined = false; hd } else Iterator.empty.next()
   }
 
-  def drop(n: Int): Iterator[A] = {
-    var i = 0
-    while (i < n && hasNext) {
-      next()
-      i += 1
-    }
-    this
-  }
+  def drop(n: Int): Iterator[A] = sliceIterator(n, -1)
 
   def dropWhile(p: A => Boolean): Iterator[A] = new AbstractIterator[A] {
     // Magic value: -1 = hasn't dropped, 0 = found first, 1 = defer to parent iterator