--- a/src/Pure/General/linear_set.scala Fri Mar 27 13:04:15 2020 +0100
+++ b/src/Pure/General/linear_set.scala Fri Mar 27 22:01:27 2020 +0100
@@ -17,7 +17,7 @@
object Linear_Set extends SetFactory[Linear_Set]
{
private val empty_val: Linear_Set[Nothing] = new Linear_Set[Nothing](None, None, Map(), Map())
- override def empty[A] = empty_val.asInstanceOf[Linear_Set[A]]
+ override def empty[A]: Linear_Set[A] = empty_val.asInstanceOf[Linear_Set[A]]
implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, Linear_Set[A]] = setCanBuildFrom[A]
def newBuilder[A]: Builder[A, Linear_Set[A]] = new SetBuilder[A, Linear_Set[A]](empty[A])