Moved the burden of forgivingness for string sl...

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

3 files changed, 33 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
 }
diff --git a/test/files/run/slice-strings.scala b/test/files/run/slice-strings.scala
new file mode 100644
index 0000000000..129314387a
--- /dev/null
+++ b/test/files/run/slice-strings.scala
@@ -0,0 +1,19 @@
+object Test {
+  def cmp(x1: String) = {
+    val x2 = x1.toList
+
+    -10 to 10 foreach { i =>
+      assert(x1.take(i) == x2.take(i).mkString)
+      assert(x1.drop(i) == x2.drop(i).mkString)
+      assert(x1.takeRight(i) == x2.takeRight(i).mkString)
+      assert(x1.dropRight(i) == x2.dropRight(i).mkString)
+    }
+    for (idx1 <- -3 to 3 ; idx2 <- -3 to 3) {
+      assert(x1.slice(idx1, idx2) == x2.slice(idx1, idx2).mkString)
+    }
+  }
+
+  def main(args: Array[String]): Unit = {
+     cmp("abcde")
+  }
+}