Merge pull request #652 from devlights:add-errors-as-go120-example

Add error_join_errorsas.go

Author: devlights

examples/basic/errs/error_join_errorsas.go

@@ -0,0 +1,80 @@
+package errs
+
+import (
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/devlights/gomy/output"
+)
+
+type MyError1 struct {
+	Message string
+	Code    int
+}
+
+type MyError2 struct {
+	Message string
+	Code    int
+}
+
+type MyError3 struct {
+	Message string
+	Code    int
+}
+
+func (me MyError1) Error() string {
+	return fmt.Sprintf("%d:%s", me.Code, me.Message)
+}
+
+func (me MyError2) Error() string {
+	return fmt.Sprintf("%d:%s", me.Code, me.Message)
+}
+
+func (me MyError3) Error() string {
+	return fmt.Sprintf("%d:%s", me.Code, me.Message)
+}
+
+// ErrorJoinErrorsAs は、Go1.20から追加された errors.Join() と errors.As() の関係性についてのサンプルです.
+func ErrorJoinErrorsAs() error {
+	var (
+		errCh = make(chan error, 1)
+	)
+	defer close(errCh)
+
+	go func(errCh chan<- error) {
+		time.Sleep(100 * time.Millisecond)
+
+		e1 := &MyError1{
+			Message: "MyError1",
+			Code:    1,
+		}
+		e2 := &MyError2{
+			Message: "MyError2",
+			Code:    2,
+		}
+
+		errCh <- errors.Join(e1, e2)
+	}(errCh)
+
+	select {
+	case <-time.After(1 * time.Second):
+	case err, ok := <-errCh:
+		if ok {
+			var e1 *MyError1
+			var e2 *MyError2
+			var e3 *MyError3
+
+			output.Stdoutl("[err  ]", err)
+			output.Stdoutl("[MyError1?]", errors.As(err, &e1))
+			output.Stdoutl("[MyError2?]", errors.As(err, &e2))
+			output.Stdoutl("[MyError3?]", errors.As(err, &e3))
+
+			output.Stdoutl("[e1]", *e1)
+			output.Stdoutl("[e2]", *e2)
+			output.Stdoutl("[e3]", e3) // e3はnilポインタとなっているのでデリファレンスするとpanicする
+		}
+	}
+
+	return nil
+}

examples/basic/errs/examples.go

@@ -20,4 +20,5 @@ func (r *register) Regist(m mapping.ExampleMapping) {
 	m["error_is_and_as"] = IsAndAs
 	m["error_join"] = ErrorJoin
 	m["error_join_fmt_errorf"] = ErrorJoinFmtErrorf
+	m["error_join_errors_as"] = ErrorJoinErrorsAs
 }