rustlings/exercises/iterators/iterators3.rs

// iterators3.rs
//
// INFO: This is a bigger exercise than most of the others! You can do it! Here is
// your mission, should you choose to accept it:
// 1. Complete the divide function to get the first four tests to pass.
// 2. Get the remaining tests to pass by completing the result_with_list and
//    list_of_results functions.
//
// Execute `rustlings hint iterators3` or use the `hint` watch subcommand for a
// hint.

#[derive(Debug, PartialEq, Eq)]
pub enum DivisionError {
    NotDivisible(NotDivisibleError),
    DivideByZero,
}

#[derive(Debug, PartialEq, Eq)]
pub struct NotDivisibleError {
    dividend: i32,
    divisor: i32,
}

// INFO: Calculate `a` divided by `b` if `a` is evenly divisible by `b`.
// Otherwise, return a suitable error.
pub fn divide(a: i32, b: i32) -> Result<i32, DivisionError> {
    if b == 0 {
        return Err(DivisionError::DivideByZero);
    }
    if a % b != 0 {
        return Err(DivisionError::NotDivisible(NotDivisibleError {
            dividend: a,
            divisor: b,
        }));
    }

    return Ok(a / b);
}

// Complete the function and return a value of the correct type so the test
// passes.
// Desired output: Ok([1, 11, 1426, 3])
fn result_with_list() -> Result<Vec<i32>, ()> {
    let numbers = vec![27, 297, 38502, 81];
    let division_results: Vec<_> = numbers.into_iter().map(|n| divide(n, 27)).collect();
    let mut new_slice: Vec<i32> = vec![];
    for n in division_results {
        match n {
            Ok(r) => new_slice.push(r),
            _ => (),
        };
    }
    Ok(new_slice)
}

// Complete the function and return a value of the correct type so the test
// passes.
// Desired output: [Ok(1), Ok(11), Ok(1426), Ok(3)]
fn list_of_results() -> Vec<Result<i32, ()>> {
    let numbers = vec![27, 297, 38502, 81];
    let division_results: Vec<_> = numbers
        .into_iter()
        .map(|n| divide(n, 27).unwrap())
        .collect();
    let mut new_output: Vec<Result<i32, ()>> = vec![];
    for x in division_results {
        new_output.push(Ok(x))
    }
    new_output
}

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

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

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

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

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

    #[test]
    fn test_result_with_list() {
        assert_eq!(format!("{:?}", result_with_list()), "Ok([1, 11, 1426, 3])");
    }

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