add a bunch of set functions

dyngeneric.go

@@ -214,6 +214,37 @@ func SetFromSlice[T comparable](items []T) Set[T] {
 	return res
 }
 
+func (s Set[T]) Clone() Set[T] {
+	res := make(Set[T], len(s))
+	for k := range s {
+		res.Add(k)
+	}
+	return res
+}
+
+func (s Set[T]) Add(item ...T) {
+	for _, i := range item {
+		s[i] = struct{}{}
+	}
+}
+
+func (s Set[T]) Has(item T) bool {
+	_, found := s[item]
+	return found
+}
+
+func (s Set[T]) Remove(item ...T) {
+	for _, i := range item {
+		delete(s, i)
+	}
+}
+
+func NewSet[T comparable](item ...T) Set[T] {
+	res := make(Set[T], len(item))
+	res.Add(item...)
+	return res
+}
+
 func (s Set[T]) String() string {
 	keys := make([]string, 0, len(s))
 	for k := range s {
@@ -226,6 +257,21 @@ func (s Set[T]) String() string {
 	return strings.Join(keys, ",")
 }
 
+// RemoveCommon removes elements from both sets that are in both,
+// leaving only the delta. Useful for Notifier on Set so that
+// oldValue has what has been removed and newValue has what has been added.
+func RemoveCommon[T comparable](a, b Set[T]) {
+	if len(a) > len(b) {
+		a, b = b, a
+	}
+	for e := range a {
+		if _, found := b[e]; found {
+			delete(a, e)
+			delete(b, e)
+		}
+	}
+}
+
 // Set updates the value from a string representation in a thread-safe manner.
 // This operation may return an error if the provided `input` doesn't parse, or the resulting value doesn't pass an
 // optional validator.

dyngeneric_test.go

@@ -49,3 +49,23 @@ func TestArrayToString(t *testing.T) {
 	assert.Equal(t, "z,a,c,b", print)
 	assert.Equal(t, "z,a,c,b", defValue)
 }
+
+func TestRemoveCommon(t *testing.T) {
+	setA := NewSet("a", "b", "c", "d")
+	setB := NewSet("b", "d", "e", "f", "g")
+	setAA := setA.Clone()
+	setBB := setB.Clone()
+	RemoveCommon(setAA, setBB)
+	assert.Equal(t, "a,c", setAA.String())   // removed
+	assert.Equal(t, "e,f,g", setBB.String()) // added
+	// Swap order to exercise the optimization on length of iteration
+	// also check clone is not modifying the original etc
+	setAA = setB.Clone() // putting B in AA on purpose and vice versa
+	setBB = setA.Clone()
+	RemoveCommon(setAA, setBB)
+	assert.Equal(t, "a,c", setBB.String())
+	assert.Equal(t, "e,f,g", setAA.String())
+	assert.True(t, setBB.Has("c"))
+	setBB.Remove("c")
+	assert.False(t, setBB.Has("c"))
+}