Merge pull request #116216 from skitt/add-generic-set-clear

Add a Clear() function to generic sets

staging/src/k8s.io/apimachinery/pkg/util/sets/set.go

@@ -64,6 +64,20 @@ func (s Set[T]) Delete(items ...T) Set[T] {
 	return s
 }
 
+// Clear empties the set.
+// It is preferable to replace the set with a newly constructed set,
+// but not all callers can do that (when there are other references to the map).
+// In some cases the set *won't* be fully cleared, e.g. a Set[float32] containing NaN
+// can't be cleared because NaN can't be removed.
+// For sets containing items of a type that is reflexive for ==,
+// this is optimized to a single call to runtime.mapclear().
+func (s Set[T]) Clear() Set[T] {
+	for key := range s {
+		delete(s, key)
+	}
+	return s
+}
+
 // Has returns true if and only if item is contained in the set.
 func (s Set[T]) Has(item T) bool {
 	_, contained := s[item]

staging/src/k8s.io/apimachinery/pkg/util/sets/set_generic_test.go

@@ -84,6 +84,57 @@ func TestSetDeleteMultiples(t *testing.T) {
 
 }
 
+func TestSetClear(t *testing.T) {
+	s := sets.Set[string]{}
+	s.Insert("a", "b", "c")
+	if s.Len() != 3 {
+		t.Errorf("Expected len=3: %d", s.Len())
+	}
+
+	s.Clear()
+	if s.Len() != 0 {
+		t.Errorf("Expected len=0: %d", s.Len())
+	}
+}
+
+func TestSetClearWithSharedReference(t *testing.T) {
+	s := sets.Set[string]{}
+	s.Insert("a", "b", "c")
+	if s.Len() != 3 {
+		t.Errorf("Expected len=3: %d", s.Len())
+	}
+
+	m := s
+	s.Clear()
+	if s.Len() != 0 {
+		t.Errorf("Expected len=0 on the cleared set: %d", s.Len())
+	}
+	if m.Len() != 0 {
+		t.Errorf("Expected len=0 on the shared reference: %d", m.Len())
+	}
+}
+
+func TestSetClearInSeparateFunction(t *testing.T) {
+	s := sets.Set[string]{}
+	s.Insert("a", "b", "c")
+	if s.Len() != 3 {
+		t.Errorf("Expected len=3: %d", s.Len())
+	}
+
+	clearSetAndAdd(s, "d")
+	if s.Len() != 1 {
+		t.Errorf("Expected len=1: %d", s.Len())
+	}
+	if !s.Has("d") {
+		t.Errorf("Unexpected contents: %#v", s)
+	}
+}
+
+func clearSetAndAdd[T comparable](s sets.Set[T], a T) {
+	s.Clear()
+	s.Insert(a)
+}
+
 func TestNewSet(t *testing.T) {
 	s := sets.New("a", "b", "c")
 	if len(s) != 3 {