Test case for #1870

Author: odersky

tests/pos/i1870.scala

@@ -0,0 +1,11 @@
+trait Stream[+A]
+case class Unfold[S,+A](s: S, f: S => Option[(A,S)]) extends Stream[A]
+
+object Test {
+  def unbox[A](s: Stream[A]) = s match {
+    case Unfold(s, f) =>
+      val s1 = s
+      val f1 = f
+      (s, f)
+  }
+}