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//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
//
/// Extension trait for `Iterator<Item = Result<O, E>>` to selectively transform Oks and Errors.
pub trait FlatMap<O, E>: Sized {
/// [flat_map](Iterator::flat_map) every `Ok` value and leave all `Err` as is
///
/// ```
/// use resiter::flat_map::FlatMap;
///
/// let mapped: Vec<_> = vec![Ok(1), Ok(2), Err(2), Err(0), Ok(2)]
/// .into_iter()
/// .flat_map_ok(|i| (0..i))
/// .collect();
/// assert_eq!(mapped, [Ok(0), Ok(0), Ok(1), Err(2), Err(0), Ok(0), Ok(1)]);
/// ```
fn flat_map_ok<U, F, O2>(self, _: F) -> FlatMapOk<Self, U, F>
where
F: FnMut(O) -> U,
U: IntoIterator<Item = O2>;
/// [flat_map](Iterator::flat_map) every `Err` value and leave all `Ok` as is
///
/// ```
/// use resiter::flat_map::FlatMap;
///
/// let mapped: Vec<_> = vec![Ok(1), Ok(2), Err(2), Err(0), Ok(2)]
/// .into_iter()
/// .flat_map_err(|i| 0..(i * 2))
/// .collect();
///
/// assert_eq!(
/// mapped,
/// [Ok(1), Ok(2), Err(0), Err(1), Err(2), Err(3), Ok(2)]
/// );
/// ```
fn flat_map_err<U, F, E2>(self, _: F) -> FlatMapErr<Self, U, F>
where
F: FnMut(E) -> U,
U: IntoIterator<Item = E2>;
}
impl<I, O, E> FlatMap<O, E> for I
where
I: Iterator<Item = Result<O, E>> + Sized,
{
#[inline]
fn flat_map_ok<U, F, O2>(self, f: F) -> FlatMapOk<Self, U, F>
where
F: FnMut(O) -> U,
U: IntoIterator<Item = O2>,
{
FlatMapOk {
frontiter: None,
iter: self,
f,
}
}
#[inline]
fn flat_map_err<U, F, E2>(self, f: F) -> FlatMapErr<Self, U, F>
where
F: FnMut(E) -> U,
U: IntoIterator<Item = E2>,
{
FlatMapErr {
frontiter: None,
iter: self,
f,
}
}
}
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct FlatMapOk<I, U, F>
where
U: IntoIterator,
{
frontiter: Option<<U as IntoIterator>::IntoIter>,
iter: I,
f: F,
}
impl<I, O, E, F, O2, U> Iterator for FlatMapOk<I, U, F>
where
I: Iterator<Item = Result<O, E>>,
F: FnMut(O) -> U,
U: IntoIterator<Item = O2>,
{
type Item = Result<O2, E>;
fn next(&mut self) -> Option<Self::Item> {
loop {
if let Some(ref mut inner) = self.frontiter {
if let elt @ Some(_) = inner.next() {
return elt.map(Ok);
}
}
match self.iter.next() {
None => return None,
Some(Ok(x)) => {
self.frontiter = Some((self.f)(x).into_iter());
}
Some(Err(e)) => return Some(Err(e)),
}
}
}
#[inline]
// TODO: Oh dear, this hint could be much better
// https://doc.rust-lang.org/src/core/iter/mod.rs.html#2694
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct FlatMapErr<I, U: IntoIterator, F> {
frontiter: Option<<U as IntoIterator>::IntoIter>,
iter: I,
f: F,
}
impl<I, O, E, F, E2, U> Iterator for FlatMapErr<I, U, F>
where
I: Iterator<Item = Result<O, E>>,
F: FnMut(E) -> U,
U: IntoIterator<Item = E2>,
{
type Item = Result<O, E2>;
fn next(&mut self) -> Option<Self::Item> {
loop {
if let Some(ref mut inner) = self.frontiter {
if let elt @ Some(_) = inner.next() {
return elt.map(Err);
}
}
match self.iter.next() {
None => return None,
Some(Err(e)) => {
self.frontiter = Some((self.f)(e).into_iter());
}
Some(Ok(o)) => return Some(Ok(o)),
}
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}