make use of pointer in generic method call

storage/sql/sql.go

@@ -13,7 +13,11 @@ type Cfg struct {
 type Rows = sql.Rows
 
 type rowsProc = func(*sql.Rows) error
-type scanner[T any] interface{ Scan(*Rows) (T, error) }
+type scanner interface{ Scan(*Rows) error }
+type sccon[T any] interface {
+	*T
+	scanner
+}
 
 type Storage struct {
 	*sql.DB
@@ -28,12 +32,15 @@ func Open(cfg *Cfg) *Storage {
 	return &Storage{db}
 }
 
-func QueryData[T scanner[T]](db *Storage, q string, args ...interface{}) []T {
+func QueryData[P interface {
+	*T
+	scanner
+}, T any](db *Storage, q string, args ...interface{}) []T {
 	var data []T
-	var rec T
+	rp := P(new(T))
 	proc := func(r *sql.Rows) error {
-		rec, err := rec.Scan(r)
-		data = append(data, rec)
+		err := rp.Scan(r)
+		data = append(data, *rp)
 		return err
 	}
 	db.Query(proc, q, args...) // ?? check error

tests/storage_test.go

@@ -35,15 +35,14 @@ type greet struct {
 	label string
 }
 
-func (g greet) Scan(rows *sql.Rows) (greet, error) {
-	err := rows.Scan(&g.id, &g.label)
-	return g, err
+func (g *greet) Scan(rows *sql.Rows) error {
+	return rows.Scan(&g.id, &g.label)
 }
 
 func BaseTest(t *testing.T, cfg *sql.Cfg, db *sql.Storage) {
 	db.Exec(insert)
 	//data := sql.QueryCol[string](db, query, 2)
-	data := sql.QueryData[greet](db, query)
+	data := sql.QueryData[*greet](db, query)
 	t.AssertEqual(len(data), 2)
 	t.AssertEqual(data[0].label, "Hello World")
 	t.AssertEqual(data[1].label, "Good Afternoon")