feat: add ErrorOrNil

README.md

@@ -21,6 +21,20 @@ go get -u github.com/gemcook/merr
 import "github.com/gemcook/merr"
 ```
 
+### Determine if it's an error
+
+```go
+multiError := merr.New()
+
+// do something...
+
+// error handling example
+if multiError.ErrorOrNil() != nil {
+    return multiError
+}
+return nil
+```
+
 ### Appends error
 
 Appends error to list of errors.
@@ -53,7 +67,7 @@ for i := 0; i < 10; i++ {
 fmt.Println(multiError.Error())
 ```
 
-```
+```text
 "something error",
 "something error",
   .
@@ -79,7 +93,7 @@ for i := 0; i < 10; i++ {
 multiError.PrettyPrint()
 ```
 
-```
+```text
 Errors[
   &errors.errorString{
     s: "something error",

errs.go

@@ -69,6 +69,7 @@ func SetNewLine(n string) {
 type Errs interface {
 	Append(err error)
 	Error() string
+	ErrorOrNil() error
 	Is(target error) bool
 	As(target interface{}) bool
 	PrettyPrint()
@@ -90,7 +91,30 @@ func (e *errs) Error() string {
 	return formatter(e)
 }
 
+func (e *errs) ErrorOrNil() error {
+	if e == nil {
+		return nil
+	}
+
+	if len(e.Errors) == 0 {
+		return nil
+	}
+
+	// If only nil is contained in the array,
+	// it is not considered an error.
+	for _, err := range e.Errors {
+		if err != nil {
+			return e
+		}
+	}
+
+	return nil
+}
+
 func (e *errs) Append(err error) {
+	if e == nil {
+		return
+	}
 	e.mx.Lock()
 	defer e.mx.Unlock()
 	if e.Errors == nil {
@@ -100,6 +124,9 @@ func (e *errs) Append(err error) {
 }
 
 func (e *errs) Is(target error) bool {
+	if e == nil {
+		return false
+	}
 	for _, err := range e.Errors {
 		if errors.Is(err, target) {
 			return true
@@ -109,6 +136,9 @@ func (e *errs) Is(target error) bool {
 }
 
 func (e *errs) As(target interface{}) bool {
+	if e == nil {
+		return false
+	}
 	for _, err := range e.Errors {
 		if errors.As(err, target) {
 			return true
@@ -118,6 +148,12 @@ func (e *errs) As(target interface{}) bool {
 }
 
 func (e *errs) PrettyPrint() {
+	if e == nil {
+		e = &errs{
+			mx:     sync.Mutex{},
+			Errors: nil,
+		}
+	}
 	fmt.Fprint(output, e.prettyFormat())
 }
 

errs_test.go

@@ -10,6 +10,10 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+type somethingError struct{}
+
+func (s *somethingError) Error() string { return "something error" }
+
 func Test_errs_Error(t *testing.T) {
 	tests := []struct {
 		name string
@@ -173,10 +177,6 @@ func Test_errs_As(t *testing.T) {
 	}
 }
 
-type somethingError struct{}
-
-func (s *somethingError) Error() string { return "something error" }
-
 func Test_errs_PrettyPrint(t *testing.T) {
 	tests := []struct {
 		name string
@@ -266,3 +266,43 @@ func TestSetNewLine(t *testing.T) {
 		})
 	}
 }
+
+func Test_errs_ErrorOrNil(t *testing.T) {
+	tests := []struct {
+		name    string
+		errs    []error
+		wantErr bool
+	}{
+		{
+			"an error",
+			[]error{
+				&somethingError{},
+			},
+			true,
+		},
+		{
+			"no error",
+			[]error{},
+			false,
+		},
+		{
+			"nil only",
+			[]error{nil},
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := New()
+			for _, e := range tt.errs {
+				err.Append(e)
+			}
+
+			if tt.wantErr {
+				assert.Error(t, err.ErrorOrNil())
+			} else {
+				assert.NoError(t, err.ErrorOrNil())
+			}
+		})
+	}
+}