Iterator::try_fold https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.try_fold提供了您需要的框架,并且从 Rust 1.27 开始就可用():
fn fold_ok<I, T, E, F>(mut iter: I, f: F) -> Result<Option<T>, E>
where
I: Iterator<Item = Result<T, E>>,
T: Ord,
F: Fn(T, T) -> T,
{
iter.try_fold(None, |r, i| {
let i = i?;
Ok(Some(if let Some(r) = r { f(r, i) } else { i }))
})
}
fn main() {
let without_errors = vec![Ok(1), Ok(2), Ok(3)];
let with_errors = vec![Ok(1), Err("error"), Ok(2)];
fn doit<'r, T>(name: &str, iter: T)
where
T: Iterator<Item = &'r Result<i32, &'static str>> + Clone,
{
println!("{}: {:?}", name, fold_ok(iter.cloned(), ::std::cmp::min));
}
doit("without errors", without_errors.iter());
doit("with errors", with_errors.iter());
}
在此之前,我认为你唯一的选择是手动迭代()
fn fold_ok<I, T, E, F>(mut iter: I, f: F) -> Result<Option<T>, E>
where
I: Iterator<Item = Result<T, E>>,
T: Ord,
F: Fn(T, T) -> T,
{
let mut result = match iter.next() {
None => return Ok(None),
Some(r) => r?,
};
for item in iter {
result = f(result, item?);
}
Ok(Some(result))
}
fn main() {
let without_errors = vec![Ok(1), Ok(2), Ok(3)];
let with_errors = vec![Ok(1), Err("error"), Ok(2)];
fn doit<'r, T>(name: &str, iter: T)
where
T: Iterator<Item = &'r Result<i32, &'static str>> + Clone,
{
println!(
"{}: {:?}",
name,
fold_ok(iter.clone().cloned(), ::std::cmp::min)
);
}
doit("without errors", without_errors.iter());
doit("with errors", with_errors.iter());
}