Moved the burden of forgivingness for string sl...

Moved the burden of forgivingness for string slices into StringOps where
it belongs. Review by odersky.

2 files changed, 14 insertions, 6 deletions

diff --git a/src/library/scala/collection/IndexedSeqOptimized.scala b/src/library/scala/collection/IndexedSeqOptimized.scala
index 59b68aaaa6..6360de33f1 100755
--- a/src/library/scala/collection/IndexedSeqOptimized.scala
+++ b/src/library/scala/collection/IndexedSeqOptimized.scala
@@ -139,16 +139,16 @@ trait IndexedSeqOptimized[+A, +Repr] extends IndexedSeqLike[A, Repr] { self =>
   def init: Repr = if (length > 0) slice(0, length - 1) else super.init
 
   override /*TraversableLike*/
-  def take(n: Int): Repr = if (n < length) slice(0, n) else slice(0, length)
+  def take(n: Int): Repr = slice(0, n)
 
   override /*TraversableLike*/
-  def drop(n: Int): Repr = if (n < length) slice(n, length) else newBuilder.result
+  def drop(n: Int): Repr = slice(n, length)
 
   override /*IterableLike*/
-  def takeRight(n: Int): Repr = if (n < length) slice(length - n, length) else slice(0, length)
+  def takeRight(n: Int): Repr = slice(length - n, length)
 
   override /*IterableLike*/
-  def dropRight(n: Int): Repr = if (n < length) slice(0, length - n) else newBuilder.result
+  def dropRight(n: Int): Repr = slice(0, length - n)
 
   override /*TraversableLike*/
   def splitAt(n: Int): (Repr, Repr) = (take(n), drop(n))
diff --git a/src/library/scala/collection/immutable/StringOps.scala b/src/library/scala/collection/immutable/StringOps.scala
index 8a27a4ad4b..0d8f5f6b83 100644
--- a/src/library/scala/collection/immutable/StringOps.scala
+++ b/src/library/scala/collection/immutable/StringOps.scala
@@ -36,8 +36,16 @@ final class StringOps(override val repr: String) extends StringLike[String] {
   /** Creates a string builder buffer as builder for this class */
   override protected[this] def newBuilder = new StringBuilder
 
-  override def slice(from: Int, until: Int): String =
-    repr.substring(from max 0, until min repr.length)
+  override def slice(from: Int, until: Int): String = {
+    /** Slice must be forgiving on all out of bounds indices and
+     *  substring is not.
+     */
+    val start = from max 0
+    val end   = until min repr.length
+
+    if (start >= end) ""
+    else repr.substring(start, end)
+  }
 
   override def toString = repr
 }