Rediscovering that transpose sometimes throws a...

Rediscovering that transpose sometimes throws an exception on irregular
lists and sometimes returns an irregular result (depending on whether
the first collection is the longest or not) indicated that this needs a
better resolution than the status quo. Determination: as long as we're
throwing an exception on any invalid input, we should throw an exception
on all invalid input, so that's what it does now. I postpone any attempt
to offer a variation accepting a "hole value". Closes #3597, review by
community.

1 files changed, 12 insertions, 0 deletions

diff --git a/test/files/run/transpose.scala b/test/files/run/transpose.scala
new file mode 100644
index 0000000000..2761a24ff5
--- /dev/null
+++ b/test/files/run/transpose.scala
@@ -0,0 +1,12 @@
+object Test {
+  def wrap[T >: Null](body: => T) =
+    try body
+    catch { case _: IllegalArgumentException => null }
+
+  def main(args: Array[String]): Unit = {
+    assert(wrap(Nil.transpose) == Nil)
+    assert(wrap(List(List(1, 2), List(1)).transpose) == null)
+    assert(wrap(List(List(1), List(1, 2)).transpose) == null)
+    assert(wrap(List(List(1, 2), List(1, 2)).transpose) == List(List(1, 1), List(2, 2)))
+  }
+}