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pub trait FilterMap<O, E>: Sized {
fn filter_map_ok<F, O2>(self, F) -> FilterMapOk<Self, F>
where
F: FnMut(O) -> Option<O2>;
fn filter_map_err<F, E2>(self, F) -> FilterMapErr<Self, F>
where
F: FnMut(E) -> Option<E2>;
}
impl<I, O, E> FilterMap<O, E> for I
where
I: Iterator<Item = Result<O, E>> + Sized,
{
fn filter_map_ok<F, O2>(self, f: F) -> FilterMapOk<Self, F>
where
F: FnMut(O) -> Option<O2>,
{
FilterMapOk { iter: self, f }
}
fn filter_map_err<F, E2>(self, f: F) -> FilterMapErr<Self, F>
where
F: FnMut(E) -> Option<E2>,
{
FilterMapErr { iter: self, f }
}
}
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct FilterMapOk<I, F> {
iter: I,
f: F,
}
impl<I, O, E, F, O2> Iterator for FilterMapOk<I, F>
where
I: Iterator<Item = Result<O, E>>,
F: FnMut(O) -> Option<O2>,
{
type Item = Result<O2, E>;
fn next(&mut self) -> Option<Self::Item> {
loop {
match self.iter.next() {
Some(Ok(x)) => {
if let Some(x) = (self.f)(x) {
return Some(Ok(x));
}
}
Some(Err(e)) => return Some(Err(e)),
None => return 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 FilterMapErr<I, F> {
iter: I,
f: F,
}
impl<I, O, E, F, E2> Iterator for FilterMapErr<I, F>
where
I: Iterator<Item = Result<O, E>>,
F: FnMut(E) -> Option<E2>,
{
type Item = Result<O, E2>;
fn next(&mut self) -> Option<Self::Item> {
loop {
match self.iter.next() {
Some(Ok(x)) => return Some(Ok(x)),
Some(Err(e)) => {
if let Some(e) = (self.f)(e) {
return Some(Err(e));
}
}
None => return None,
}
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
#[test]
fn test_filter_map_ok() {
use std::str::FromStr;
let filter_mapped: Vec<_> = vec![
Ok("1"),
Err("2"),
Ok("a"),
Err("4"),
Ok("5"),
Err("b"),
Err("8"),
].into_iter()
.filter_map_ok(|txt| usize::from_str(txt).ok())
.filter_map_err(|txt| usize::from_str(txt).ok().map(|i| i * 3))
.collect();
assert_eq!(filter_mapped[0], Ok(1));
assert_eq!(filter_mapped[1], Err(2 * 3));
assert_eq!(filter_mapped[2], Err(4 * 3));
assert_eq!(filter_mapped[3], Ok(5));
assert_eq!(filter_mapped[4], Err(8 * 3));
}
#[test]
fn test_filter_map_ok_hint() {
use std::str::FromStr;
let hint = ["1", "2", "a", "4", "5"]
.into_iter()
.map(|txt| usize::from_str(txt))
.filter_map_ok(|i| Some(2 * i))
.size_hint();
assert_eq!(hint, (5, Some(5)));
}
#[test]
fn test_filter_map_err_hint() {
use std::str::FromStr;
let hint = ["1", "2", "a", "4", "5"]
.into_iter()
.map(|txt| usize::from_str(txt))
.filter_map_err(|e| Some(format!("{:?}", e)))
.size_hint();
assert_eq!(hint, (5, Some(5)));
}