WORK IN PROGRESS: New representation for arrays of value classes

src/dotty/DottyPredef.scala

@@ -1,7 +1,9 @@
 package dotty
 
+import scala.collection.mutable.WrappedArray
 import scala.reflect.ClassTag
 import scala.reflect.runtime.universe.TypeTag
+import scala.runtime.ScalaRunTime.arrayElementClass
 import scala.Predef.???  // this is currently ineffective, because of #530
 
 abstract class I1 {
@@ -34,4 +36,15 @@ object DottyPredef extends I6 {
 
   /** ClassTags for final classes */
   implicit val NothingClassTag: ClassTag[Nothing] = ClassTag.Nothing
+
+  // This implicit will never be used for arrays of primitives because
+  // the wrap*Array in scala.Predef have a higher priority.
+  implicit def wrapVCArray[T <: AnyVal](xs: Array[T]): WrappedArray[T] =
+    new WrappedArray[T] {
+      val array = xs
+      lazy val elemTag = ClassTag[T](arrayElementClass(array.getClass))
+      def length: Int = array.length
+      def apply(index: Int): T = array(index)
+      def update(index: Int, elem: T) { array(index) = elem }
+    }
 }

src/dotty/runtime/Arrays.scala

@@ -22,6 +22,11 @@ object Arrays {
     arr
   }
 
+  /** Method used only to remember the unerased type of an array of
+   *  value class after erasure.
+   */
+  def vcArray[T <: AnyVal](xs: Array[T], clazz: Class[_]): Array[T] = ???
+
   /** Create an array of type T. T must be of form Array[E], with
    *  E being a reference type.
    */