Make specialization pick up opportunities when the

specialized method has additional (non-specialized) type parameters.

This fix comes from Stefan's desire to specialize HLists (see 
corresponding test). review by @prokopec

1 files changed, 29 insertions, 0 deletions

diff --git a/test/files/specialized/spec-hlists.scala b/test/files/specialized/spec-hlists.scala
new file mode 100644
index 0000000000..8c4ac8f610
--- /dev/null
+++ b/test/files/specialized/spec-hlists.scala
@@ -0,0 +1,29 @@
+/** Test contributed by Stefan Zeiger showing that HLists can be
+ *  specialized.
+ */
+
+sealed trait HList {
+  type Self <: HList
+  
+  type |: [E] = HCons[E, Self]
+
+  final def |: [@specialized E](elem: E): |: [E] = new HCons[E, Self](elem, this.asInstanceOf[Self])
+
+  def m[@specialized E, T <: AnyRef](x: E): T = null.asInstanceOf[T]
+}
+
+final class HCons[@specialized H, T <: HList](val head: H, val tail: T) extends HList {
+  type Self = HCons[H, T]
+}
+
+final object HNil extends HList {
+  type Self = HNil.type
+}
+
+object Test extends App {
+  val l1 = new HCons(42, "foo" |: HNil)
+  println(l1.getClass)
+  
+  val l2 = 42 |: "abc" |: HNil
+  println(l2.getClass)
+}