util/set: add Of variant of SetOf that takes variadic parameter

set.Of(1, 2, 3) is prettier than set.SetOf([]int{1, 2, 3}).

I was going to change the signature of SetOf but then I noticed its
name has stutter anyway, so I kept it for compatibility. People can
prefer to use set.Of for new code or slowly migrate.

Also add a lazy Make method, which I often find myself wanting,
without having to resort to uglier mak.Set(&set, k, struct{}{}).

Updates #cleanup

Change-Id: Ic6f3870115334efcbd65e79c437de2ad3edb7625
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

util/set/set.go

@@ -14,6 +14,11 @@ 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] {
+	return Of(slice...)
+}
+
+// Of returns a new set constructed from the elements in slice.
+func Of[T comparable](slice ...T) Set[T] {
 	s := make(Set[T])
 	s.AddSlice(slice)
 	return s
@@ -41,6 +46,13 @@ func (s Set[T]) AddSet(es Set[T]) {
 	}
 }
 
+// Make lazily initializes the map pointed to by s to be non-nil.
+func (s *Set[T]) Make() {
+	if *s == nil {
+		*s = make(Set[T])
+	}
+}
+
 // 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 {

util/set/set_test.go

@@ -53,7 +53,7 @@ func TestSet(t *testing.T) {
 }
 
 func TestSetOf(t *testing.T) {
-	s := SetOf[int]([]int{1, 2, 3, 4, 4, 1})
+	s := Of(1, 2, 3, 4, 4, 1)
 	if s.Len() != 4 {
 		t.Errorf("wrong len %d; want 4", s.Len())
 	}
@@ -74,20 +74,20 @@ func TestEqual(t *testing.T) {
 	tests := []test{
 		{
 			"equal",
-			SetOf([]int{1, 2, 3, 4}),
-			SetOf([]int{1, 2, 3, 4}),
+			Of(1, 2, 3, 4),
+			Of(1, 2, 3, 4),
 			true,
 		},
 		{
 			"not equal",
-			SetOf([]int{1, 2, 3, 4}),
-			SetOf([]int{1, 2, 3, 5}),
+			Of(1, 2, 3, 4),
+			Of(1, 2, 3, 5),
 			false,
 		},
 		{
 			"different lengths",
-			SetOf([]int{1, 2, 3, 4, 5}),
-			SetOf([]int{1, 2, 3, 5}),
+			Of(1, 2, 3, 4, 5),
+			Of(1, 2, 3, 5),
 			false,
 		},
 	}
@@ -100,7 +100,7 @@ func TestEqual(t *testing.T) {
 }
 
 func TestClone(t *testing.T) {
-	s := SetOf[int]([]int{1, 2, 3, 4, 4, 1})
+	s := Of(1, 2, 3, 4, 4, 1)
 	if s.Len() != 4 {
 		t.Errorf("wrong len %d; want 4", s.Len())
 	}
@@ -122,8 +122,8 @@ func TestSetJSONRoundTrip(t *testing.T) {
 	}{
 		{"empty", make(Set[string]), make(Set[int])},
 		{"nil", nil, nil},
-		{"one-item", SetOf([]string{"one"}), SetOf([]int{1})},
-		{"multiple-items", SetOf([]string{"one", "two", "three"}), SetOf([]int{1, 2, 3})},
+		{"one-item", Of("one"), Of(1)},
+		{"multiple-items", Of("one", "two", "three"), Of(1, 2, 3)},
 	}
 	for _, tt := range tests {
 		t.Run(tt.desc, func(t *testing.T) {
@@ -158,3 +158,12 @@ func TestSetJSONRoundTrip(t *testing.T) {
 		})
 	}
 }
+
+func TestMake(t *testing.T) {
+	var s Set[int]
+	s.Make()
+	s.Add(1)
+	if !s.Contains(1) {
+		t.Error("missing 1")
+	}
+}