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{}

binding/default_validator_benchmark_test.go

@@ -0,0 +1,20 @@
+package binding
+
+import (
+	"errors"
+	"strconv"
+	"testing"
+)
+
+func BenchmarkSliceValidateError(b *testing.B) {
+	const size int = 100
+	for i := 0; i < b.N; i++ {
+		e := make(sliceValidateError, size)
+		for j := 0; j < size; j++ {
+			e[j] = errors.New(strconv.Itoa(j))
+		}
+		if len(e.Error()) == 0 {
+			b.Errorf("error")
+		}
+	}
+}

binding/default_validator_test.go

@@ -16,6 +16,26 @@ func TestSliceValidateError(t *testing.T) {
 		want string
 	}{
 		{"has nil elements", sliceValidateError{errors.New("test error"), nil}, "[0]: test error"},
+		{"has zero elements", sliceValidateError{}, ""},
+		{"has one element", sliceValidateError{errors.New("test one error")}, "[0]: test one error"},
+		{"has two elements",
+			sliceValidateError{
+				errors.New("first error"),
+				errors.New("second error"),
+			},
+			"[0]: first error\n[1]: second error",
+		},
+		{"has many elements",
+			sliceValidateError{
+				errors.New("first error"),
+				errors.New("second error"),
+				nil,
+				nil,
+				nil,
+				errors.New("last error"),
+			},
+			"[0]: first error\n[1]: second error\n[5]: last error",
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {