Improve performance and behavior of ListMap and ListSet

Makes the immutable `ListMap` and `ListSet` collections more alike one another, both in their semantics and in their performance.

In terms of semantics, makes the `ListSet` iterator return the elements in their insertion order, as `ListMap` already does. While, as mentioned in SI-8985, `ListMap` and `ListSet` doesn't seem to make any guarantees in terms of iteration order, I believe users expect `ListSet` and `ListMap` to behave in the same way, particularly when they are implemented in the exact same way.

In terms of performance, `ListSet` has a custom builder that avoids creation in O(N^2) time. However, this significantly reduces its performance in the creation of small sets, as its requires the instantiation and usage of an auxilliary HashSet. As `ListMap` and `ListSet` are only suitable for small sizes do to their performance characteristics, the builder is removed, the default `SetBuilder` being used instead.

1 files changed, 0 insertions, 6 deletions

diff --git a/test/files/run/t7445.scala b/test/files/run/t7445.scala
deleted file mode 100644
index e4ffeb8e1a..0000000000
--- a/test/files/run/t7445.scala
+++ /dev/null
@@ -1,6 +0,0 @@
-import scala.collection.immutable.ListMap
-
-object Test extends App {
-	val a = ListMap(1 -> 1, 2 -> 2, 3 -> 3, 4 -> 4, 5 -> 5);
-	require(a.tail == ListMap(2 -> 2, 3 -> 3, 4 -> 4, 5 -> 5));
-}