fix type parameters for QueryData()

storage/sql/sql.go

@@ -13,7 +13,7 @@ type Cfg struct {
 type Rows = sql.Rows
 
 type rowsProc = func(*sql.Rows) error
-type Scanner interface{ Scan(*Rows) (Scanner, error) }
+type Scanner[T any] interface{ Scan(*Rows) (T, error) }
 
 type Storage struct {
 	*sql.DB
@@ -28,12 +28,11 @@ func Open(cfg *Cfg) *Storage {
 	return &Storage{db}
 }
 
-func QueryData[T Scanner](db *Storage, q string, args ...interface{}) []T {
+func QueryData[T Scanner[T]](db *Storage, q string, args ...interface{}) []T {
 	var data []T
 	proc := func(r *sql.Rows) error {
 		var rec T
-		r1, err := rec.Scan(r)
-		rec = r1.(T)
+		rec, err := rec.Scan(r)
 		data = append(data, rec)
 		return err
 	}

tests/storage_test.go

@@ -35,7 +35,7 @@ type greet struct {
 	label string
 }
 
-func (g greet) Scan(rows *sql.Rows) (sql.Scanner, error) {
+func (g greet) Scan(rows *sql.Rows) (greet, error) {
 	err := rows.Scan(&g.id, &g.label)
 	return g, err
 }