util/set: add some useful utility functions for Set (#9535)

Also give each type of set its own file.

Updates #cleanup

Signed-off-by: Chris Palmer <cpalmer@tailscale.com>

util/set/set.go

@@ -7,9 +7,33 @@ package set
 // Set is a set of T.
 type Set[T comparable] map[T]struct{}
 
+// SetOf returns a new set constructed from the elements in slice.
+func SetOf[T comparable](slice []T) Set[T] {
+	s := make(Set[T])
+	s.AddSlice(slice)
+	return s
+}
+
 // Add adds e to the set.
 func (s Set[T]) Add(e T) { s[e] = struct{}{} }
 
+// AddSlice adds each element of es to the set.
+func (s Set[T]) AddSlice(es []T) {
+	for _, e := range es {
+		s.Add(e)
+	}
+}
+
+// Slice returns the elements of the set as a slice. The elements will not be
+// in any particular order.
+func (s Set[T]) Slice() []T {
+	es := make([]T, 0, s.Len())
+	for k := range s {
+		es = append(es, k)
+	}
+	return es
+}
+
 // Delete removes e from the set.
 func (s Set[T]) Delete(e T) { delete(s, e) }
 
@@ -21,27 +45,3 @@ func (s Set[T]) Contains(e T) bool {
 
 // Len reports the number of items in s.
 func (s Set[T]) Len() int { return len(s) }
-
-// HandleSet is a set of T.
-//
-// It is not safe for concurrent use.
-type HandleSet[T any] map[Handle]T
-
-// Handle is a opaque comparable value that's used as the map key
-// in a HandleSet. The only way to get one is to call HandleSet.Add.
-type Handle struct {
-	v *byte
-}
-
-// Add adds the element (map value) e to the set.
-//
-// It returns the handle (map key) with which e can be removed, using a map
-// delete.
-func (s *HandleSet[T]) Add(e T) Handle {
-	h := Handle{new(byte)}
-	if *s == nil {
-		*s = make(HandleSet[T])
-	}
-	(*s)[h] = e
-	return h
-}