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What is the idiomatic way to write a map closure with a result type? Do I just collect it as a result and use a ? On it? Doesn’t that make the iteration occur twice? #rust #rustlang

3/12/25, 9:16 pm0 reposts0 likes

Vincent Sgherzi

@vincents.dev

3 Dec 2025

The alternative to seem to be to just use a for loop or pay another iteration penalty like I did above… Surely there’s a more elegant solution?

adamfortune.bsky.social

@adamfortune.bsky.social

4 Dec 2025

If I remember correctly, Result is an IntoIterator type, so you could flat_map instead of map if you’re just trying to ignore the Err’s.

Vincent Sgherzi

@vincents.dev

4 Dec 2025

What if I want to early return if there’s any error

adamfortune.bsky.social

@adamfortune.bsky.social

4 Dec 2025

I think you could replace starting at .collect() with .map(|result| result .map(/* your Ok value logic */)) .take_until(|result| result .is_err() .fold(|result| { let aggregate = result?/* rest of the fold logic here */ }) I use [take_until](docs.rs/take-until/l...), but take_while could work too

docs.rsTakeUntilExt in take_until - RustTakeUntilExt is an extension trait for iterators. It adds the `Self::take_until` method.

Vincent Sgherzi

@vincents.dev

4 Dec 2025

Oooo neat, thanks !