lib/uuidv7: implement Equal method for [lib/reflect.Equaler]

The Equal method returns nil if both receiver and parameter has
the same value.
This method implements [lib/reflect.Equaler] interface.

2 files changed, 40 insertions, 0 deletions

diff --git a/lib/uuidv7/uuidv7.go b/lib/uuidv7/uuidv7.go
index 5a6b6e03..6870b562 100644
--- a/lib/uuidv7/uuidv7.go
+++ b/lib/uuidv7/uuidv7.go
@@ -77,6 +77,27 @@ func (id UUIDv7) Bytes() (data []byte) {
 	return data
 }
 
+// Equal returns nil if id and v are equals.
+// This method implements [git.sr.ht/~shulhan/pakakeh.go/lib/reflect.Equaler]
+// interface.
+func (id *UUIDv7) Equal(v any) (err error) {
+	ptr, ok := v.(*UUIDv7)
+	if !ok {
+		other, ok := v.(UUIDv7)
+		if !ok {
+			return fmt.Errorf(`uuidv7: Equal: want type %T, got %T`, &id, v)
+		}
+		ptr = &other
+	}
+	if id.high != ptr.high {
+		return fmt.Errorf(`uuidv7: not equal, want %s, got %s`, id.String(), ptr.String())
+	}
+	if id.low != ptr.low {
+		return fmt.Errorf(`uuidv7: not equal, want %s, got %s`, id.String(), ptr.String())
+	}
+	return nil
+}
+
 // IsZero returns true if all bits is zero.
 func (id UUIDv7) IsZero() bool {
 	return id.high == 0 && id.low == 0
diff --git a/lib/uuidv7/uuidv7_example_test.go b/lib/uuidv7/uuidv7_example_test.go
index c0472dd5..df007698 100644
--- a/lib/uuidv7/uuidv7_example_test.go
+++ b/lib/uuidv7/uuidv7_example_test.go
@@ -46,6 +46,25 @@ func ExampleParse() {
 	// false 019CD2F8-1AE3-774E-BFFF-FFFFFFFFFFFF 2026-03-09 14:20:01.123 +0000 UTC
 }
 
+func ExampleUUIDv7_Equal() {
+	id := uuidv7.Parse(`019CD2F8-1AE3-774E-BFFF-FFFFFFFFFFFF`)
+	id2 := uuidv7.Parse(`019CD2F8-2AE3-774E-BFFF-FFFFFFFFFFFF`)
+
+	err := id.Equal(id)
+	fmt.Printf("%v\n", err)
+
+	err = id.Equal(&id)
+	fmt.Printf("%v\n", err)
+
+	err = id.Equal(&id2)
+	fmt.Printf("%v\n", err)
+
+	// Output:
+	// <nil>
+	// <nil>
+	// uuidv7: not equal, want 019CD2F8-1AE3-774E-BFFF-FFFFFFFFFFFF, got 019CD2F8-2AE3-774E-BFFF-FFFFFFFFFFFF
+}
+
 func ExampleUUIDv7_MarshalBinary() {
 	now := time.Date(2026, 3, 9, 14, 20, 0, 123456700, time.UTC)
 	uuidv7.Now = func() time.Time {