Ejemplo de tipos algebraicos en Rust

algebraicTypes.rs

pub mod flight_discount {
    pub trait Discount {
        fn percentage(self: Self) -> u8;
    }

    #[allow(dead_code)]
    pub enum SpanishSubsidy {
        LargeFamily,
        ResidentOfIslandsOrCeuta,
        SpecialResidentLargeFamily,
        None,
    }

    impl Discount for SpanishSubsidy {
        fn percentage(self: Self) -> u8 {
            match self {
                SpanishSubsidy::LargeFamily => 10,
                SpanishSubsidy::ResidentOfIslandsOrCeuta => 75,
                SpanishSubsidy::SpecialResidentLargeFamily => 85,
                _ => 0
            }
        }
    }

    #[allow(dead_code)]
    pub enum FlightDiscount {
        Business,
        SubsidyPlusBusiness,
        NoDiscount,
    }

    impl Discount for FlightDiscount {
        fn percentage(self) -> u8 {
            match self {
                FlightDiscount::Business => 5,
                FlightDiscount::SubsidyPlusBusiness => {
                    SpanishSubsidy::ResidentOfIslandsOrCeuta.percentage() +
                        FlightDiscount::Business.percentage()
                }
                FlightDiscount::NoDiscount => 0
            }
        }
    }

    pub fn calculate_discount_percentage<T: Discount>(discount: T) -> u8 {
        discount.percentage()
    }

}

#[cfg(test)]
mod flight_discount_tests {
    use crate::flight_discount::{calculate_discount_percentage, SpanishSubsidy, FlightDiscount};

    // Spanish subsidy tests
    #[test]
    fn spanish_subsidy_for_large_family_is_10() {
        assert_eq!(
            calculate_discount_percentage(SpanishSubsidy::LargeFamily),
            10
        );
    }

    #[test]
    fn spanish_subsidy_for_residents_of_islands_or_ceuta_is_75() {
        assert_eq!(
            calculate_discount_percentage(SpanishSubsidy::ResidentOfIslandsOrCeuta),
            75
        );
    }

    #[test]
    fn spanish_subsidy_for_large_family_residents_of_islands_or_ceuta_is_85() {
        assert_eq!(
            calculate_discount_percentage(SpanishSubsidy::SpecialResidentLargeFamily),
            85
        );
    }

    #[test]
    fn default_spanish_subsidy_is_zero() {
        assert_eq!(
            calculate_discount_percentage(SpanishSubsidy::None),
            0
        );
    }

    // Flight discount tests
    #[test]
    fn flight_discount_for_business_is_5() {
        assert_eq!(
            calculate_discount_percentage(FlightDiscount::Business),
            5
        );
    }

    #[test]
    fn flight_discount_for_subsidy_plus_business_is_80() {
        assert_eq!(
            calculate_discount_percentage(FlightDiscount::SubsidyPlusBusiness),
            80
        );
    }

    #[test]
    fn flight_discount_with_no_discount_is_zero() {
        assert_eq!(
            calculate_discount_percentage(FlightDiscount::NoDiscount),
            0
        );
    }
}