this post was submitted on 17 Jan 2022
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Rust Programming

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"Rust needs evert(), which turns an iterator over Result of T into a Result of a collection of T or a collection of errors" Thoughts on this? (cybre.space)
submitted 2 years ago by AgreeableLandscape@lemmy.ml to c/rust@lemmy.ml
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[โ€“] asonix@lemmy.ml 1 points 2 years ago* (last edited 2 years ago) (1 children)

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,
    }
});

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]));
}