RFC: add `try_all` and `try_any` to `Iterator` by FlixCoder · Pull Request #3233...
source link: https://github.com/rust-lang/rfcs/pull/3233
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As this is my first RFC / PR here, I am sorry if there is something missing or wrong.
Thank you for reviewing and suggestions :)
changed the title
Proposal to add try_all and try_any to Iterator
RFC: add try_all and try_any to Iterator
In some cases where one would like to use `any`/`all`, the actual condition to check is fallible. For example, let's say we have a simple key-value-store like a `HashMap`. The keys are IDs to the objects. We further have a list of IDs we want to check some condition on. We would like to use `all` on an iterator over the list to ensure all objects match our condition. However, access to elements is fallable and returns `Option`s. In other cases, the checks might involve more complex validation on the objects. The validation method could involve access to external parts and fail. Therefore, it returns a `Result<bool, Error>`.
The implementor needs to return a `bool` for every element in `all`. They could use `.try_fold(true, |state, item| Ok(state && check(item)?))`, but this is less readable and does not short-circuit as `all` does. If they would do `.all(|item| check(item).unwrap_or(false))`, the error would be discarded and lost/ignored. To fully comply with expectations, there is only two possibilites (I see):
Short-circuiting on both is probably easiest done with try_for_each, something like
let r = it.try_for_each(|x| match check(x) {
Ok(b) => if b { ControlFlow::Continue(()) } else { ControlFlow::Break(Ok(false)) },
e => ControlFlow::Break(e),
});
let r = match r {
ControlFlow::Continue(()) => Ok(true),
ControlFlow::Break(r) => r,
};But yes, that's of course much less readable than having the method provided by Iterator.
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