Merge pull request #1828 from paulp/pr/stream-lengthCompare

SI-6415, Stream#lengthCompare

2 files changed, 21 insertions, 13 deletions

diff --git a/src/library/scala/collection/LinearSeqOptimized.scala b/src/library/scala/collection/LinearSeqOptimized.scala
index 0f0a405a85..81cccea519 100755
--- a/src/library/scala/collection/LinearSeqOptimized.scala
+++ b/src/library/scala/collection/LinearSeqOptimized.scala
@@ -12,6 +12,7 @@ import generic._
 import mutable.ListBuffer
 import immutable.List
 import scala.util.control.Breaks._
+import scala.annotation.tailrec
 
 /** A template trait for linear sequences of type `LinearSeq[A]`  which optimizes
  *  the implementation of several methods under the assumption of fast linear access.
@@ -247,14 +248,17 @@ trait LinearSeqOptimized[+A, +Repr <: LinearSeqOptimized[A, Repr]] extends Linea
   }
 
   override /*SeqLike*/
-  def lengthCompare(len: Int): Int =  {
-    var i = 0
-    var these = self
-    while (!these.isEmpty && i <= len) {
-      i += 1
-      these = these.tail
+  def lengthCompare(len: Int): Int = {
+    @tailrec def loop(i: Int, xs: Repr): Int = {
+      if (i == len)
+        if (xs.isEmpty) 0 else 1
+      else if (xs.isEmpty)
+        -1
+      else
+        loop(i + 1, xs.tail)
     }
-    i - len
+    if (len < 0) 1
+    else loop(0, this)
   }
 
   override /*SeqLike*/
diff --git a/src/library/scala/collection/SeqLike.scala b/src/library/scala/collection/SeqLike.scala
index f65e2ef9cd..1be0dba29f 100644
--- a/src/library/scala/collection/SeqLike.scala
+++ b/src/library/scala/collection/SeqLike.scala
@@ -84,13 +84,17 @@ trait SeqLike[+A, +Repr] extends Any with IterableLike[A, Repr] with GenSeqLike[
    *  if computing `length` is cheap.
    */
   def lengthCompare(len: Int): Int = {
-    var i = 0
-    val it = iterator
-    while (it.hasNext && i <= len) {
-      it.next()
-      i += 1
+    if (len < 0) 1
+    else {
+      var i = 0
+      val it = iterator
+      while (it.hasNext) {
+        if (i == len) return if (it.hasNext) 1 else 0
+        it.next()
+        i += 1
+      }
+      i - len
     }
-    i - len
   }
 
   override /*IterableLike*/ def isEmpty: Boolean = lengthCompare(0) == 0