func (s Set[T]) String() string {
	return fmt.Sprintf("%v", s.UnsortedList())
}

// InsertOrNew inserts t into the set if the set exists, or returns a new set with t if not.
// Works well with DeleteCleanupLast.
// Example:
//
//	InsertOrNew(m, key, value)
func InsertOrNew[K comparable, T comparable](m map[K]Set[T], k K, v T) {
	s, f := m[k]
	if !f {
		m[k] = New(v)
	} else {

			b.StopTimer()
			s := New(sortOrder...)
			b.StartTimer()
			SortedList(s)
		}
	})
}

func TestMapOfSet(t *testing.T) {
	m := map[int]String{}
	InsertOrNew(m, 1, "a")
	InsertOrNew(m, 1, "b")
	InsertOrNew(m, 2, "c")
	assert.Equal(t, m, map[int]String{1: New("a", "b"), 2: New("c")})

	DeleteCleanupLast(m, 1, "a")
	assert.Equal(t, m, map[int]String{1: New("b"), 2: New("c")})

// multiple values.
type MultiValueMap map[string]sets.String

// Insert adds given (key, value) pair into the map.
func (m MultiValueMap) Insert(key, value string) MultiValueMap {
	sets.InsertOrNew(m, key, value)
	return m
}

// Delete removes given (key, value) pair out of the map.
func (m MultiValueMap) Delete(key, value string) MultiValueMap {
	sets.DeleteCleanupLast(m, key, value)
	return m

				sets.DeleteCleanupLast(idx.objects, indexKey, key)
			}
		}
		if o.New != nil {
			obj := *o.New
			key := GetKey(obj)
			for _, indexKey := range extract(obj) {
				sets.InsertOrNew(idx.objects, indexKey, key)
			}
		}
	})

	return &idx

		mu:      sync.RWMutex{},
	}
	addObj := func(obj any) {
		ro := controllers.ExtractObject(obj)
		o := ro.(O)
		objectKey := config.NamespacedName(o)
		for _, indexKey := range extract(o) {
			sets.InsertOrNew(idx.objects, indexKey, objectKey)
		}
	}
	deleteObj := func(obj any) {
		ro := controllers.ExtractObject(obj)
		o := ro.(O)
		objectKey := config.NamespacedName(o)
		for _, indexKey := range extract(o) {

	filter := map[string]sets.String{}
	for _, name := range names {
		dir, _, hn, p := model.ParseSubsetKey(name)
		defaultKey := model.BuildSubsetKey(dir, "", hn, p)
		sets.InsertOrNew(filter, defaultKey, name)
	}
	return filter
}

// clusterBuilder is responsible for building a single default and subset clusters for a service
// TODO re-use the v1alpha3.ClusterBuilder: