maps: make Clone preserve nil map
The x/exp/maps.Clone function doesn't preserve nil
the way x/exp/slices.Clone does, but it should be.
Fixes golang/go#53817
Change-Id: Ib1867fb6e31d990d8b8a846e9dba8a5b6ba83c48
Reviewed-on: https://go-review.googlesource.com/c/exp/+/417274
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
diff --git a/maps/maps.go b/maps/maps.go
index f49768b..ecc0dab 100644
--- a/maps/maps.go
+++ b/maps/maps.go
@@ -63,6 +63,10 @@
// Clone returns a copy of m. This is a shallow clone:
// the new keys and values are set using ordinary assignment.
func Clone[M ~map[K]V, K comparable, V any](m M) M {
+ // Preserve nil in case it matters.
+ if m == nil {
+ return nil
+ }
r := make(M, len(m))
for k, v := range m {
r[k] = v
diff --git a/maps/maps_test.go b/maps/maps_test.go
index c21ef30..bf7c6f4 100644
--- a/maps/maps_test.go
+++ b/maps/maps_test.go
@@ -142,6 +142,14 @@
}
}
+func TestCloneNil(t *testing.T) {
+ var m1 map[string]int
+ mc := Clone(m1)
+ if mc != nil {
+ t.Errorf("Clone(%v) = %v, want %v", m1, mc, m1)
+ }
+}
+
func TestCopy(t *testing.T) {
mc := Clone(m1)
Copy(mc, mc)
