fn to_model(&self) -> anyhow::Result<Self::Model> {

        let mut rule = RecurrenceRule::empty_with_capacity(self.len());

        for part in self.iter() {

            match part {

                RecurRulePart::Freq(f) => {

                    rule = rule.set_freq(f.clone());

                }

                RecurRulePart::Until(date_time) => {

                    let dt = date_time.to_model()?;

                    rule = rule.set_until(dt);

                RecurRulePart::Count(count) => {

                    rule = rule.set_count(*count);

                }

                RecurRulePart::Interval(interval) => {

                    rule = rule.set_interval(*interval);

                }

                RecurRulePart::BySecList(by_sec_list) => {

                    rule = rule.set_by_second(by_sec_list.clone());

                }

                RecurRulePart::ByMinute(by_minute) => {

                    rule = rule.set_by_minute(by_minute.clone());

                }

                RecurRulePart::ByHour(by_hour) => {

                    rule = rule.set_by_hour(by_hour.clone());

                }

                RecurRulePart::ByDay(by_day) => {

                    rule = rule.set_by_day(by_day.clone());

                }

                RecurRulePart::ByMonthDay(by_month_day) => {

                    rule = rule.set_by_month_day(by_month_day.clone());

                }

                RecurRulePart::ByYearDay(by_year_day) => {

                    rule = rule.set_by_year_day(by_year_day.clone());

                }

                RecurRulePart::ByWeek(week) => {

                    rule = rule.set_by_week_number(week.clone());

                }

                RecurRulePart::ByMonth(month) => {

                    rule = rule.set_by_month(

                        month

                            .iter()

                            .map(|m| time::Month::try_from(*m).context("Invalid month"))

                            .collect::<anyhow::Result<Vec<_>>>()?,

                RecurRulePart::BySetPos(by_set_pos) => {

                    rule = rule.set_by_set_pos(by_set_pos.clone());

                }

                RecurRulePart::WeekStart(week_start) => {

                    rule = rule.set_week_start(week_start.clone());

                }

        Ok(rule)

    }