SI-8474 Inconsistent behavior of patch method

Changed Iterator to be consistent with other collections.

Also fixed SeqViewLike to validate/constrain inputs.

No specific tests; quasi-comprehensive collection tests will cover this later.

1 files changed, 29 insertions, 11 deletions

diff --git a/src/library/scala/collection/Iterator.scala b/src/library/scala/collection/Iterator.scala
index f6f46e158f..660cc5a42a 100644
--- a/src/library/scala/collection/Iterator.scala
+++ b/src/library/scala/collection/Iterator.scala
@@ -1088,6 +1088,9 @@ trait Iterator[+A] extends TraversableOnce[A] {
   }
 
   /** Returns this iterator with patched values.
+   *  Patching at negative indices is the same as patching starting at 0.
+   *  Patching at indices at or larger than the length of the original iterator appends the patch to the end.
+   *  If more values are replaced than actually exist, the excess is ignored.
    *
    *  @param from       The start index from which to patch
    *  @param patchElems The iterator of patch values
@@ -1096,18 +1099,33 @@ trait Iterator[+A] extends TraversableOnce[A] {
    */
   def patch[B >: A](from: Int, patchElems: Iterator[B], replaced: Int): Iterator[B] = new AbstractIterator[B] {
     private var origElems = self
-    private var i = 0
-    def hasNext: Boolean =
-      if (i < from) origElems.hasNext
-      else patchElems.hasNext || origElems.hasNext
+    private var i = (if (from > 0) from else 0)  // Counts down, switch to patch on 0, -1 means use patch first
+    def hasNext: Boolean = {
+      if (i == 0) {
+        origElems = origElems drop replaced
+        i = -1
+      }
+      origElems.hasNext || patchElems.hasNext
+    }
     def next(): B = {
-      // We have to do this *first* just in case from = 0.
-      if (i == from) origElems = origElems drop replaced
-      val result: B =
-        if (i < from || !patchElems.hasNext) origElems.next()
-        else patchElems.next()
-      i += 1
-      result
+      if (i == 0) {
+        origElems = origElems drop replaced
+        i = -1
+      }
+      if (i < 0) {
+        if (patchElems.hasNext) patchElems.next()
+        else origElems.next()
+      }
+      else {
+        if (origElems.hasNext) {
+          i -= 1
+          origElems.next()
+        }
+        else {
+          i = -1
+          patchElems.next()
+        }
+      }
     }
   }