From ad6983518dd6860564d16f5b6e99178db3cff7a2 Mon Sep 17 00:00:00 2001
From: Jason Zaugg <jzaugg@gmail.com>
Date: Tue, 5 Mar 2013 10:27:41 +0100
Subject: SI-7215 Fix transpose of an empty Array[Array[T]].

---
 .../scala/collection/mutable/ArrayOps.scala        | 23 ++++++++++++----------
 test/files/run/t7215.scala                         |  6 ++++++
 2 files changed, 19 insertions(+), 10 deletions(-)
 create mode 100644 test/files/run/t7215.scala

diff --git a/src/library/scala/collection/mutable/ArrayOps.scala b/src/library/scala/collection/mutable/ArrayOps.scala
index bb938a7aeb..25ba7e4ce6 100644
--- a/src/library/scala/collection/mutable/ArrayOps.scala
+++ b/src/library/scala/collection/mutable/ArrayOps.scala
@@ -76,18 +76,21 @@ trait ArrayOps[T] extends Any with ArrayLike[T, Array[T]] with CustomParalleliza
    *  @return         An array obtained by replacing elements of this arrays with rows the represent.
    */
   def transpose[U](implicit asArray: T => Array[U]): Array[Array[U]] = {
-    def mkRowBuilder() = Array.newBuilder(ClassTag[U](arrayElementClass(elementClass)))
-    val bs = asArray(head) map (_ => mkRowBuilder())
-    for (xs <- this) {
-      var i = 0
-      for (x <- asArray(xs)) {
-        bs(i) += x
-        i += 1
+    val bb: Builder[Array[U], Array[Array[U]]] = Array.newBuilder(ClassTag[Array[U]](elementClass))
+    if (isEmpty) bb.result()
+    else {
+      def mkRowBuilder() = Array.newBuilder(ClassTag[U](arrayElementClass(elementClass)))
+      val bs = asArray(head) map (_ => mkRowBuilder())
+      for (xs <- this) {
+        var i = 0
+        for (x <- asArray(xs)) {
+          bs(i) += x
+          i += 1
+        }
       }
+      for (b <- bs) bb += b.result()
+      bb.result()
     }
-    val bb: Builder[Array[U], Array[Array[U]]] = Array.newBuilder(ClassTag[Array[U]](elementClass))
-    for (b <- bs) bb += b.result
-    bb.result
   }
 
   def seq = thisCollection
diff --git a/test/files/run/t7215.scala b/test/files/run/t7215.scala
new file mode 100644
index 0000000000..c93e97f9c8
--- /dev/null
+++ b/test/files/run/t7215.scala
@@ -0,0 +1,6 @@
+object Test extends App {
+  List[List[Any]]().transpose.isEmpty
+  Array[Array[Any]]().transpose.isEmpty
+  Vector[Vector[Any]]().transpose.isEmpty
+  Stream[Stream[Any]]().transpose.isEmpty
+}
-- 
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