Uh... what?
So I understand the type signature she's asking for is Iter<Result<T, E>> -> Result<Iter<T>, Iter<E>>
This suggestion could really use some use case examples. It sounds sufficiently obscure to me that I wouldn't complain about having to write my own a function for this
Also, where does the name evert come from?
I can see this being useful for parsing. You often want to report all of the parsing errors to the user in one go, so collecting them into a list or iterator is useful.
But yeah, still relatively obscure.
And I'm guessing, "evert" is simply the respective English word: https://en.wiktionary.org/wiki/evert
As a non-native speaker, I didn't know that word either...
I'm a native english speaker and I didn't know that word :o
I think she is talking about this functionality which already exists. It is not very intuitive though.
let res = my_collection
.iter()
.map(|x| method_that_returns_result(x))
.collect::<Result<Vec<T>, Error>>()?;
So it turns a Vec<Result, Error> into Result<Vec<T>, Error>, and you can turn it into Vec<T> simply with ?. Otherwise you would probably need a for loop.
do you mean Vec<Result<T, Error>>? why would an error type be the second type argument for a Vec?
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]));
}