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pub trait AndThen<O, E>: Sized {
fn and_then_ok<F, O2>(self, F) -> AndThenOk<Self, F>
where
F: FnMut(O) -> Result<O2, E>;
fn and_then_err<F, E2>(self, F) -> AndThenErr<Self, F>
where
F: FnMut(E) -> Result<O, E2>;
}
impl<I, O, E> AndThen<O, E> for I
where
I: Iterator<Item = Result<O, E>> + Sized,
{
fn and_then_ok<F, O2>(self, f: F) -> AndThenOk<Self, F>
where
F: FnMut(O) -> Result<O2, E>,
{
AndThenOk { iter: self, f }
}
fn and_then_err<F, E2>(self, f: F) -> AndThenErr<Self, F>
where
F: FnMut(E) -> Result<O, E2>,
{
AndThenErr { iter: self, f }
}
}
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct AndThenOk<I, F> {
iter: I,
f: F,
}
impl<I, O, E, O2, F> Iterator for AndThenOk<I, F>
where
I: Iterator<Item = Result<O, E>>,
F: FnMut(O) -> Result<O2, E>,
{
type Item = Result<O2, E>;
fn next(&mut self) -> Option<Self::Item> {
match self.iter.next() {
Some(Ok(o)) => Some((self.f)(o)),
Some(Err(e)) => Some(Err(e)),
None => None,
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct AndThenErr<I, F> {
iter: I,
f: F,
}
impl<I, O, E, E2, F> Iterator for AndThenErr<I, F>
where
I: Iterator<Item = Result<O, E>>,
F: FnMut(E) -> Result<O, E2>,
{
type Item = Result<O, E2>;
fn next(&mut self) -> Option<Self::Item> {
match self.iter.next() {
Some(Err(e)) => Some((self.f)(e)),
Some(Ok(o)) => Some(Ok(o)),
None => None,
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
#[test]
fn test_and_then_ok() {
use std::str::FromStr;
let mapped: Vec<_> = ["1", "2", "a", "b", "4", "5"]
.into_iter()
.map(|txt| usize::from_str(txt).map_err(|e| (txt, e)))
.and_then_ok(|i| Ok(2 * i))
.and_then_err(|(txt, e)| if txt == &"a" { Ok(15) } else { Err(e) })
.collect();
assert_eq!(mapped[0], Ok(2));
assert_eq!(mapped[1], Ok(4));
assert_eq!(mapped[2], Ok(15));
assert!(mapped[3].is_err());
assert_eq!(mapped[4], Ok(8));
assert_eq!(mapped[5], Ok(10));
}