Fix of pos/t2454

"_" type paraeters need to be given fresh names.

1 files changed, 39 insertions, 0 deletions

diff --git a/tests/pos/t2421_delitedsl.scala b/tests/pos/t2421_delitedsl.scala
new file mode 100644
index 000000000..554702a03
--- /dev/null
+++ b/tests/pos/t2421_delitedsl.scala
@@ -0,0 +1,39 @@
+trait DeliteDSL {
+  abstract class <~<[-From, +To] extends (From => To)
+  implicit def trivial[A]: A <~< A = new (A <~< A) {def apply(x: A) = x}
+
+  trait Forcible[T]
+  object Forcible {
+    def factory[T](f: T => Forcible[T]) = new (T <~< Forcible[T]){def apply(x: T) = f(x)}
+  }
+
+  case class DeliteInt(x: Int) extends Forcible[Int]
+
+  implicit val forcibleInt: DeliteDSL.this.<~<[Int,DeliteDSL.this.Forcible[Int]] =
+    Forcible.factory((x: Int) => DeliteInt(x))
+
+  import scala.collection.Traversable
+  class DeliteCollection[T](val xs: Traversable[T]) {
+    // must use existential in bound of P, instead of T itself, because we cannot both have:
+        // Test.x below: DeliteCollection[T=Int] -> P=DeliteInt <: Forcible[T=Int], as T=Int <~< P=DeliteInt
+        // Test.xAlready below: DeliteCollection[T=DeliteInt] -> P=DeliteInt <: Forcible[T=DeliteInt], as T=DeliteInt <~< P=DeliteInt
+        // this would required DeliteInt <: Forcible[Int] with Forcible[DeliteInt]
+
+    def headProxy[P <: Forcible[_]](implicit w: T <~< P): P = xs.head
+  }
+  // If T is already a proxy (it is forcible), the compiler should use
+  // forcibleIdentity to deduce that P=T.  If T is Int, the compiler
+  // should use intToForcible to deduce that P=DeliteInt.
+  //
+  // Without this feature, the user must write 'xs.proxyOfFirst[DeliteInt]',
+  // with the feature they can write 'xs.proxyOfFirst', which is shorter and
+  // avoids exposing internal DELITE types to the world.
+
+  object Test {
+    val x = new DeliteCollection(List(1,2,3)).headProxy
+    // inferred: val x: Forcible[Int] = new DeliteCollection[Int](List.apply[Int](1, 2, 3)).headProxy[Forcible[Int]](forcibleInt);
+
+    val xAlready = new DeliteCollection(List(DeliteInt(1),DeliteInt(2),DeliteInt(3))).headProxy
+    // inferred: val xAlready: DeliteInt = new DeliteCollection[DeliteInt](List.apply[DeliteInt](DeliteInt(1), DeliteInt(2), DeliteInt(3))).headProxy[DeliteInt](trivial[DeliteInt]);
+  }
+}