✨Nora Tindall (@tindall@cybre.space)
cybre.space
Rust needs evert(), which turns an iterator over Result of T into a Result of a collection of T or a collection of errors currently the most ergonomic way to do this is to wrap a whole pipeline in a function boundary and use `?`.
  • Aode (He/They)
    2•2 years ago

    i might try

    let res = collection.into_iter().map(|item| item.fallible_operation()).fold(Ok(Vec::new()), |acc, res| {
    match (acc, res) {
        (Ok(mut vec), Ok(item)) => {
            vec.push(item);
            Ok(vec)
        }
        (Err(mut vec), Err(error)) => {
            vec.push(error);
            Err(vec)
        }
        (Ok(_), Err(error)) => Err(vec![error]),
        (acc, _) => acc,
    }
});

    Maybe expand it with

    pub trait Evert<T, E> {
    fn evert(self) -> Result<Vec<T>, Vec<E>>;
}

impl<I, T, E> Evert<T, E> for I
where
    I: IntoIterator<Item = Result<T, E>>,
{
    fn evert(self) -> Result<Vec<T>, Vec<E>> {
        self.into_iter().fold(/* implementation from above */)
    }
}

fn main() {
    let result = vec![Ok(1), Err(3), Ok(4), Err(8)].evert();
    assert_eq!(result, Err(vec![3, 8]));
}