Use X <: Tuple bound for Tuple.{Init|Last}

Author: danicheg

library/src/scala/Tuple.scala

@@ -84,15 +84,12 @@ object Tuple {
   }
 
   /** Type of the initial part of the tuple without its last element */
-  type Init[X <: NonEmptyTuple] <: Tuple = X match {
+  @experimental
+  type Init[X <: Tuple] <: Tuple = X match {
+    case EmptyTuple => EmptyTuple
     case _ *: EmptyTuple => EmptyTuple
     case x *: xs =>
-      xs match {
-        case _ *: EmptyTuple =>
-          x *: EmptyTuple
-        case _ =>
-          x *: Init[xs]
-      }
+      x *: Init[xs]
   }
 
   /** Type of the tail of a tuple */
@@ -101,13 +98,15 @@ object Tuple {
   }
 
   /** Type of the last of a tuple */
-  type Last[X <: NonEmptyTuple] = Reduce[X, EmptyTuple] match {
+  @experimental
+  type Last[X <: Tuple] = Reduce[X, EmptyTuple] match {
     case x *: xs => xs match {
       case EmptyTuple => x
     }
   }
 
   /** Type of the reduce of the first tuple to a tuple of arity 1 or provide the second tuple as a result */
+  @experimental
   type Reduce[X <: Tuple, Y <: Tuple] <: Tuple = X match {
     case EmptyTuple => Y
     case x *: xs => xs match {