Merge pull request #231 from xmidt-org/more-is

More is

example_extend_test.go

@@ -0,0 +1,83 @@
+// SPDX-FileCopyrightText: 2025 Comcast Cable Communications Management, LLC
+// SPDX-License-Identifier: Apache-2.0
+
+package wrp_test
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/xmidt-org/wrp-go/v5"
+)
+
+type Extended struct {
+	wrp.SimpleEvent
+	Extra string
+}
+
+var _ wrp.Union = (*Extended)(nil)
+
+// Implement the wrp.Union interface for the Extended type.
+func (e *Extended) MsgType() wrp.MessageType {
+	return wrp.SimpleEventMessageType
+}
+
+// Implement the wrp.Union interface for the Extended type.
+func (e *Extended) To(msg *wrp.Message, v ...wrp.Processor) error {
+	e.SimpleEvent.Headers = []string{"extra: " + e.Extra}
+	return e.SimpleEvent.To(msg, v...)
+}
+
+// Implement the wrp.Union interface for the Extended type.
+func (e *Extended) From(msg *wrp.Message, v ...wrp.Processor) error {
+	err := e.SimpleEvent.From(msg, v...)
+	if err != nil {
+		return err
+	}
+
+	e.Extra = ""
+	if len(e.SimpleEvent.Headers) > 0 {
+		after, found := strings.CutPrefix(e.SimpleEvent.Headers[0], "extra: ")
+		if found {
+			e.Extra = after
+		}
+	}
+
+	return nil
+}
+
+// Implement the wrp.Union interface for the Extended type.
+func (e *Extended) Validate(v ...wrp.Processor) error {
+	return e.SimpleEvent.Validate(v...)
+}
+
+// Is reports whether the msg is the same type as the target, or is convertible
+// to the target, without the need to validate the message.  This function is not
+// part of the wrp.Union interface, but it is a useful function to have when working
+// with the wrp.Union interface.
+func (e *Extended) Is(msg wrp.Union) bool {
+	var tmp wrp.SimpleEvent
+	if wrp.As(msg, &tmp, wrp.NoStandardValidation()) == nil {
+		if len(tmp.Headers) > 0 && strings.HasPrefix(tmp.Headers[0], "extra: ") {
+			return true
+		}
+	}
+
+	return false
+}
+
+func Example_extend() {
+	isExtended := wrp.SimpleEvent{
+		Headers: []string{"extra: something"},
+	}
+	isNotExtended := wrp.SimpleEvent{}
+
+	// The Extended type is a wrp.Union, so it can be used in the wrp.Is function.
+	// The wrp.Is function is useful for determining if the type matches, even if
+	// the message doesn't validate.
+	fmt.Printf("isExtended:    %t\n", wrp.Is(&isExtended, &Extended{}))
+	fmt.Printf("isNotExtended: %t\n", wrp.Is(&isNotExtended, &Extended{}))
+
+	// Output: isExtended:    true
+	// isNotExtended: false
+}

is.go

@@ -9,6 +9,14 @@ package wrp
 // If the validators are not provided, the msg will be validated against the
 // default validators.  To skip validation, provide the NoStandardValidation()
 // as a validator.
+//
+// If the target implements the Is(Union) bool method, that method will be
+// called to determine if the msg is the same type as the target.  If the target
+// does not implement the Is(Union) method, the msg will be converted into a
+// *Message and validated against the validators.
+//
+// Is() is valuable for determining if the type matches, even if the message
+// doesn't validate.
 func Is(msg, target Union, validators ...Processor) bool {
 	if msg == nil || target == nil {
 		return msg == nil && target == nil
@@ -21,6 +29,10 @@ func Is(msg, target Union, validators ...Processor) bool {
 		return false
 	}
 
+	if t, ok := target.(interface{ Is(Union) bool }); ok {
+		return t.Is(msg)
+	}
+
 	if m, ok := msg.(*Message); ok {
 		if err := m.Validate(validators...); err != nil {
 			return false

is_test.go

@@ -10,6 +10,38 @@ import (
 	"github.com/xmidt-org/wrp-go/v5"
 )
 
+// This type is here to show that a type that implements the wrp.Union interface
+// can be used in the wrp.Is function.  The Is() function is beyond the scope of
+// of the wrp.Union interface, but it is a useful function to have when working
+// with the wrp.Union interface as it allows the caller to determine if the
+// message is of a specific type - even if it doesn't validate..
+type isTest struct {
+	is bool
+}
+
+var _ wrp.Union = (*isTest)(nil)
+
+func (i *isTest) MsgType() wrp.MessageType {
+	return wrp.UnknownMessageType
+}
+
+func (i *isTest) To(msg *wrp.Message, v ...wrp.Processor) error {
+	msg.Type = wrp.UnknownMessageType
+	return nil
+}
+
+func (i *isTest) From(msg *wrp.Message, v ...wrp.Processor) error {
+	return nil
+}
+
+func (i *isTest) Validate(v ...wrp.Processor) error {
+	return nil
+}
+
+func (i *isTest) Is(msg wrp.Union) bool {
+	return i.is
+}
+
 func TestIs(t *testing.T) {
 	tests := []struct {
 		desc       string
@@ -68,6 +100,11 @@ func TestIs(t *testing.T) {
 			msg:    &wrp.Unknown{},
 			target: &wrp.Message{Type: wrp.UnknownMessageType},
 			want:   true,
+		}, {
+			desc:   "msg type matches exact type",
+			msg:    &wrp.Message{Type: wrp.UnknownMessageType},
+			target: &isTest{is: true},
+			want:   true,
 		}, {
 			desc:   "msg type is not the same type",
 			msg:    &wrp.Message{Type: wrp.UnknownMessageType},