improve sliceValidateError.Error performance using switch and strings.Builder (#2765)

fix missing nil pointer check

use simpler switch case

add missing tests

use for-loop instead of range

add benchmark test codes

binding/default_validator.go

@@ -20,15 +20,27 @@ type defaultValidator struct {
 
 type sliceValidateError []error
 
+// Error concatenates all error elements in sliceValidateError into a single string separated by \n.
 func (err sliceValidateError) Error() string {
-	var errMsgs []string
-	for i, e := range err {
-		if e == nil {
-			continue
+	n := len(err)
+	switch n {
+	case 0:
+		return ""
+	default:
+		var b strings.Builder
+		if err[0] != nil {
+			fmt.Fprintf(&b, "[%d]: %s", 0, err[0].Error())
 		}
-		errMsgs = append(errMsgs, fmt.Sprintf("[%d]: %s", i, e.Error()))
+		if n > 1 {
+			for i := 1; i < n; i++ {
+				if err[i] != nil {
+					b.WriteString("\n")
+					fmt.Fprintf(&b, "[%d]: %s", i, err[i].Error())
+				}
+			}
+		}
+		return b.String()
 	}
-	return strings.Join(errMsgs, "\n")
 }
 
 var _ StructValidator = &defaultValidator{}