support calling query sequences multiples times

Signed-off-by: Achille Roussel <achille.roussel@gmail.com>

sqlrange.go

@@ -192,8 +192,7 @@ func Query[Row any](q Queryable, query string, args ...any) iter.Seq2[Row, error
 // QueryContext returns the results of the query as a sequence of rows.
 //
 // The returned function automatically closes the unerlying sql.Rows value when
-// it completes its iteration. The function can only be iterated once, it will
-// not retain the values that it has seen.
+// it completes its iteration.
 //
 // A typical use of QueryContext is:
 //
@@ -210,21 +209,20 @@ func Query[Row any](q Queryable, query string, args ...any) iter.Seq2[Row, error
 // See Scan for more information about how the rows are mapped to the row type
 // parameter Row.
 func QueryContext[Row any](ctx context.Context, q Queryable, query string, args ...any) iter.Seq2[Row, error] {
-	rows, err := q.QueryContext(ctx, query, args...)
-	if err != nil {
-		return func(yield func(Row, error) bool) {
+	return func(yield func(Row, error) bool) {
+		if rows, err := q.QueryContext(ctx, query, args...); err != nil {
 			var zero Row
 			yield(zero, err)
+		} else {
+			scan[Row](yield, rows)
 		}
 	}
-	return Scan[Row](rows)
 }
 
 // Scan returns a sequence of rows from a sql.Rows value.
 //
 // The returned function automatically closes the rows passed as argument when
-// it completes its iteration. The function can only be iterated once, it will
-// not retain the values that it has seen.
+// it completes its iteration.
 //
 // A typical use of Scan is:
 //
@@ -254,40 +252,42 @@ func QueryContext[Row any](ctx context.Context, q Queryable, query string, args
 // Ranging over the returned function will panic if the type parameter is not a
 // struct.
 func Scan[Row any](rows *sql.Rows) iter.Seq2[Row, error] {
-	return func(yield func(Row, error) bool) {
-		defer rows.Close()
-		var zero Row
+	return func(yield func(Row, error) bool) { scan(yield, rows) }
+}
 
-		columns, err := rows.Columns()
-		if err != nil {
-			yield(zero, err)
-			return
-		}
+func scan[Row any](yield func(Row, error) bool, rows *sql.Rows) {
+	defer rows.Close()
+	var zero Row
 
-		scanArgs := make([]any, len(columns))
-		row := new(Row)
-		val := reflect.ValueOf(row).Elem()
+	columns, err := rows.Columns()
+	if err != nil {
+		yield(zero, err)
+		return
+	}
 
-		for columnName, structField := range Fields(val.Type()) {
-			if columnIndex := slices.Index(columns, columnName); columnIndex >= 0 {
-				scanArgs[columnIndex] = val.FieldByIndex(structField.Index).Addr().Interface()
-			}
-		}
+	scanArgs := make([]any, len(columns))
+	row := new(Row)
+	val := reflect.ValueOf(row).Elem()
 
-		for rows.Next() {
-			if err := rows.Scan(scanArgs...); err != nil {
-				yield(zero, err)
-				return
-			}
-			if !yield(*row, nil) {
-				return
-			}
-			*row = zero
+	for columnName, structField := range Fields(val.Type()) {
+		if columnIndex := slices.Index(columns, columnName); columnIndex >= 0 {
+			scanArgs[columnIndex] = val.FieldByIndex(structField.Index).Addr().Interface()
 		}
+	}
 
-		if err := rows.Err(); err != nil {
+	for rows.Next() {
+		if err := rows.Scan(scanArgs...); err != nil {
 			yield(zero, err)
+			return
+		}
+		if !yield(*row, nil) {
+			return
 		}
+		*row = zero
+	}
+
+	if err := rows.Err(); err != nil {
+		yield(zero, err)
 	}
 }