Merge pull request #23 from gkdr/use-scanner

feat(option): if T is sql.Scanner, use it in Scan()

option.go

@@ -2,6 +2,7 @@ package mo
 
 import (
 	"bytes"
+	"database/sql"
 	"database/sql/driver"
 	"encoding/gob"
 	"encoding/json"
@@ -257,14 +258,27 @@ func (o *Option[T]) GobDecode(data []byte) error {
 	return o.UnmarshalBinary(data)
 }
 
-// Scan implements the SQL driver.Scanner interface.
+// Scan implements the SQL sql.Scanner interface.
 func (o *Option[T]) Scan(src any) error {
 	if src == nil {
 		o.isPresent = false
 		o.value = empty[T]()
 		return nil
 	}
 
+	// is is only possible to assert interfaces, so convert first
+	// https://go.googlesource.com/proposal/+/refs/heads/master/design/43651-type-parameters.md#why-not-permit-type-assertions-on-values-whose-type-is-a-type-parameter
+	var t T
+	if tScanner, ok := interface{}(&t).(sql.Scanner); ok {
+		if err := tScanner.Scan(src); err != nil {
+			return fmt.Errorf("failed to scan: %w", err)
+		}
+
+		o.isPresent = true
+		o.value = t
+		return nil
+	}
+
 	if av, err := driver.DefaultParameterConverter.ConvertValue(src); err == nil {
 		if v, ok := av.(T); ok {
 			o.isPresent = true

option_test.go

@@ -3,6 +3,7 @@ package mo
 import (
 	"database/sql"
 	"encoding/json"
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -413,3 +414,42 @@ func TestOptionValue(t *testing.T) {
 	is.EqualValues(None[string](), option2)
 	is.Nil(err2)
 }
+
+type SomeScanner struct {
+	Cool bool
+	Some int
+}
+
+func (ss *SomeScanner) Scan(src any) error {
+	val, ok := src.(string)
+	if !ok {
+		return fmt.Errorf("cannot scan - src is not a string")
+	}
+
+	var unmarshalled SomeScanner
+	if err := json.Unmarshal([]byte(val), &unmarshalled); err != nil {
+		return fmt.Errorf("failed to unmarshal json: %w", err)
+	}
+
+	*ss = unmarshalled
+	return nil
+}
+
+// If T is a sql.Scanner, make use of that.
+func TestOptionScanner(t *testing.T) {
+	is := assert.New(t)
+
+	jsonString := `{"cool": true, "some": 123}`
+	nullString, _ := sql.NullString{}.Value()
+
+	var someScanner Option[SomeScanner]
+	var noneScanner Option[SomeScanner]
+
+	err1 := someScanner.Scan(jsonString)
+	err2 := noneScanner.Scan(nullString)
+
+	is.NoError(err1)
+	is.EqualValues(Some(SomeScanner{Cool: true, Some: 123}), someScanner)
+	is.NoError(err2)
+	is.EqualValues(None[SomeScanner](), noneScanner)
+}