Хозяйке на заметку: let future_returns_db_connection = ...; let prog = future_returns_db_connection.and_then(|db_connection| { your_stream_wants_to_work_with_db.fold(db_connection, |also_db_connection, value| { also_db_connection.just_another_db_query_moveouts_connection_and_return_a_new_one() }) })