public static function get_course_grades_returns() {
        return new external_single_structure(
            array(
                'grades' => new external_multiple_structure(
                    new external_single_structure(
                        array(
                            'courseid' => new external_value(PARAM_INT, 'Course id'),
                            'grade' => new external_value(PARAM_RAW, 'Grade formatted'),
                            'rawgrade' => new external_value(PARAM_RAW, 'Raw grade, not formatted'),
                            'rank' => new external_value(PARAM_INT, 'Your rank in the course', VALUE_OPTIONAL),
                        )
                    )
                ),
                'warnings' => new external_warnings()
            )
        );
    }