Rust snippets

add_trait.rs

#[derive(Debug, PartialEq)]
enum Currency {DOLLAR, EURO}

#[derive(Debug, PartialEq)]
struct Money {
    currency: Currency,
    amount: u8,
}

impl std::ops::Add for Money {
    type Output = Result<Self, &'static str>;

    fn add(self, money: Self) -> Self::Output {
        if  money.currency != self.currency {
            return Err("Can not operate with different currencies")
        }
        Ok(Money {
            currency: self.currency,
            amount: self.amount + money.amount,
        })
    }
}


#[test]
fn should_add_money_with_same_currency() {
    let ten_dollars = Money {
        currency: Currency::DOLLAR,
        amount: 10,
    };
    let five_dollars = Money {
        currency: Currency::DOLLAR,
        amount: 5,
    };
    let fifteen = ten_dollars + five_dollars;
    assert!(fifteen.is_ok(),true);
    assert_eq!(fifteen.ok().unwrap().amount,15);
}

#[test]
fn should_not_allow_add_money_with_different_currency() {
    let ten_dollars = Money {
        currency: Currency::DOLLAR,
        amount: 10,
    };
    let five_euros = Money {
        currency: Currency::EURO,
        amount: 5,
    };
    let fifteen = ten_dollars + five_euros;
    assert!(fifteen.is_err(),true);
}