types/opt: use switch in Bool.UnmarshalJSON (#9140)

The compiler does indeed perform this optimization.

Updates #cleanup

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

types/opt/bool.go

@@ -87,21 +87,15 @@ func (b Bool) MarshalJSON() ([]byte, error) {
 }
 
 func (b *Bool) UnmarshalJSON(j []byte) error {
-	// Note: written with a bunch of ifs instead of a switch
-	// because I'm sure the Go compiler optimizes away these
-	// []byte->string allocations in an == comparison, but I'm too
-	// lazy to check whether that's true in a switch also.
-	if string(j) == "true" {
+	switch string(j) {
+	case "true":
 		*b = "true"
-		return nil
-	}
-	if string(j) == "false" {
+	case "false":
 		*b = "false"
-		return nil
-	}
-	if string(j) == "null" {
+	case "null":
 		*b = "unset"
-		return nil
-	}
+	default:
 		return fmt.Errorf("invalid opt.Bool value %q", j)
 	}
+	return nil
+}

types/opt/bool_test.go

@@ -119,3 +119,11 @@ func TestBoolEqualBool(t *testing.T) {
 		}
 	}
 }
+
+func TestUnmarshalAlloc(t *testing.T) {
+	b := json.Unmarshaler(new(Bool))
+	n := testing.AllocsPerRun(10, func() { b.UnmarshalJSON(trueBytes) })
+	if n > 0 {
+		t.Errorf("got %v allocs, want 0", n)
+	}
+}