rustlings/exercises/18_iterators/iterators3.rs

use std::f32::consts::E;

#[derive(Debug, PartialEq, Eq)]
enum DivisionError {
    // Example: 42 / 0
    DivideByZero,
    // Only case for `i64`: `i64::MIN / -1` because the result is `i64::MAX + 1`
    IntegerOverflow,
    // Example: 5 / 2 = 2.5
    NotDivisible,
}

// Otherwise, return a suitable error.
fn divide(a: i64, b: i64) -> Result<i64, DivisionError> {
    if b == 0 {
        return Err(DivisionError::DivideByZero)
    }
    match a.checked_rem(b) {
        None => {
            Err(DivisionError::IntegerOverflow)
        }
        Some(0) => {
            let division = a.checked_div(b);
            if let Some(result) = division {
                Ok(result)
            } else {
                Err(DivisionError::IntegerOverflow)
            }
        },
        Some(_) => {
            Err(DivisionError::NotDivisible)
        }
    }
}

// Desired output: `Ok([1, 11, 1426, 3])`
fn result_with_list() -> Result<Vec<i64>, DivisionError> {
    let numbers = [27, 297, 38502, 81];
    let division_results = numbers.into_iter().map(|n| divide(n, 27));
    Ok(division_results.map(|i| {
        i.unwrap()
    }).collect::<Vec<i64>>())
}

// Desired output: `[Ok(1), Ok(11), Ok(1426), Ok(3)]`
fn list_of_results() -> Vec<Result<i64, DivisionError>>{
    let numbers = [27, 297, 38502, 81];
    let division_results = numbers.into_iter().map(|n| divide(n, 27));
    division_results.collect()
}

fn main() {
    // You can optionally experiment here.
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_success() {
        assert_eq!(divide(81, 9), Ok(9));
    }

    #[test]
    fn test_divide_by_0() {
        assert_eq!(divide(81, 0), Err(DivisionError::DivideByZero));
    }

    #[test]
    fn test_integer_overflow() {
        assert_eq!(divide(i64::MIN, -1), Err(DivisionError::IntegerOverflow));
    }

    #[test]
    fn test_not_divisible() {
        assert_eq!(divide(81, 6), Err(DivisionError::NotDivisible));
    }

    #[test]
    fn test_divide_0_by_something() {
        assert_eq!(divide(0, 81), Ok(0));
    }

    #[test]
    fn test_result_with_list() {
        assert_eq!(result_with_list().unwrap(), [1, 11, 1426, 3]);
    }

    #[test]
    fn test_list_of_results() {
        assert_eq!(list_of_results(), [Ok(1), Ok(11), Ok(1426), Ok(3)]);
    }
}