Made mkString work correctly on views.

about how to obtain a String and how not to. Closes #4297, no review.

5 files changed, 30 insertions, 2 deletions

diff --git a/src/library/scala/collection/TraversableViewLike.scala b/src/library/scala/collection/TraversableViewLike.scala
index 0c01cb893e..8d94a7f381 100644
--- a/src/library/scala/collection/TraversableViewLike.scala
+++ b/src/library/scala/collection/TraversableViewLike.scala
@@ -200,9 +200,19 @@ self =>
     buf.result
   }
 
+  // Have to overload all three to work around #4299.  The overload
+  // is because mkString should force a view but toString should not.
+  override def mkString: String = mkString("")
+  override def mkString(sep: String): String = mkString("", sep, "")
+  override def mkString(start: String, sep: String, end: String): String = {
+    thisSeq.addString(new StringBuilder(), start, sep, end).toString
+  }
+
   override def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder =
     b append start append "..." append end
 
+  override def toString = stringPrefix+"(...)"
+
   override def filter(p: A => Boolean): This = newFiltered(p).asInstanceOf[This]
   override def withFilter(p: A => Boolean): This = newFiltered(p).asInstanceOf[This]
   override def partition(p: A => Boolean): (This, This) = (filter(p), filter(!p(_)))
diff --git a/src/library/scala/collection/mutable/StringBuilder.scala b/src/library/scala/collection/mutable/StringBuilder.scala
index 6c3715e560..73d3778650 100644
--- a/src/library/scala/collection/mutable/StringBuilder.scala
+++ b/src/library/scala/collection/mutable/StringBuilder.scala
@@ -432,11 +432,24 @@ final class StringBuilder(private val underlying: JavaStringBuilder)
 
   /** Returns a new String representing the data in this sequence.
    *
+   *  @note    because toString is inherited from AnyRef and used for
+   *           many purposes, it is better practice to call mkString
+   *           to obtain a StringBuilder result.
    *  @return  the current contents of this sequence as a String
    */
   override def toString = underlying.toString
+
+  /** Returns a new String representing the data in this sequence.
+   *
+   *  @return  the current contents of this sequence as a String
+   */
   override def mkString = toString
 
+  /** Returns the result of this Builder, which in the case
+   *  of StringBuilders is a StringBuilder (not a String.)
+   *
+   *  @return  this StringBuilder
+   */
   def result(): StringBuilder = this
 }
 
diff --git a/src/library/scala/collection/parallel/ParIterableView.scala b/src/library/scala/collection/parallel/ParIterableView.scala
index 0bcad549a2..f8e0f9909c 100644
--- a/src/library/scala/collection/parallel/ParIterableView.scala
+++ b/src/library/scala/collection/parallel/ParIterableView.scala
@@ -13,7 +13,6 @@ package scala.collection.parallel
 
 
 import scala.collection.Parallel
-import scala.collection.TraversableViewLike
 import scala.collection.IterableView
 import scala.collection.generic.CanCombineFrom
 
diff --git a/src/library/scala/collection/parallel/ParIterableViewLike.scala b/src/library/scala/collection/parallel/ParIterableViewLike.scala
index d34aa10977..2b7bd03e7a 100644
--- a/src/library/scala/collection/parallel/ParIterableViewLike.scala
+++ b/src/library/scala/collection/parallel/ParIterableViewLike.scala
@@ -13,7 +13,6 @@ package scala.collection.parallel
 
 
 import scala.collection.Parallel
-import scala.collection.TraversableViewLike
 import scala.collection.IterableView
 import scala.collection.IterableViewLike
 import scala.collection.generic.CanBuildFrom
diff --git a/test/files/run/bug4297.scala b/test/files/run/bug4297.scala
new file mode 100644
index 0000000000..7497dfe4c2
--- /dev/null
+++ b/test/files/run/bug4297.scala
@@ -0,0 +1,7 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    def f = List(1,2,3).view
+    assert(f.toString == "SeqView(...)")
+    assert(f.mkString == "123")
+  }
+}