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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 Flatten<O, E>: Sized {
/// [flatten](Iterator::flatten) `Ok` values while leaving `Err`-values as is.
///
/// ```
/// use resiter::flatten::Flatten;
/// use resiter::map::Map;
///
/// let mapped: Vec<_> = vec![Ok(1), Ok(2), Err(2), Err(0), Ok(2)]
/// .into_iter()
/// .map_ok(|i| (0..i))
/// .map_err(|i| 0..(i * 2))
/// .flatten_ok()
/// .collect();
///
/// assert_eq!(
/// mapped,
/// [Ok(0), Ok(0), Ok(1), Err(0..4), Err(0..0), Ok(0), Ok(1)]
/// );
/// ```
fn flatten_ok<U, O2>(self) -> FlattenOk<Self, U>
where
U: IntoIterator<Item = O2>;
/// [flatten](Iterator::flatten) `Err` values while leaving `Ok`-values as is.
///
/// ```
/// use resiter::flatten::Flatten;
/// use resiter::map::Map;
///
/// let mapped: Vec<_> = vec![Ok(1), Ok(2), Err(2), Err(0), Ok(2)]
/// .into_iter()
/// .map_ok(|i| (0..i))
/// .map_err(|i| 0..(i * 2))
/// .flatten_err()
/// .collect();
///
/// assert_eq!(
/// mapped,
/// [
/// Ok(0..1),
/// Ok(0..2),
/// Err(0),
/// Err(1),
/// Err(2),
/// Err(3),
/// Ok(0..2),
/// ]
/// );
/// ```
fn flatten_err<U, E2>(self) -> FlattenErr<Self, U>
where
U: IntoIterator<Item = E2>;
}
impl<I, O, E> Flatten<O, E> for I
where
I: Iterator<Item = Result<O, E>> + Sized,
{
#[inline]
fn flatten_ok<U, O2>(self) -> FlattenOk<Self, U>
where
U: IntoIterator<Item = O2>,
{
FlattenOk {
frontiter: None,
iter: self,
}
}
#[inline]
fn flatten_err<U, E2>(self) -> FlattenErr<Self, U>
where
U: IntoIterator<Item = E2>,
{
FlattenErr {
frontiter: None,
iter: self,
}
}
}
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct FlattenOk<I, U>
where
U: IntoIterator,
{
frontiter: Option<<U as IntoIterator>::IntoIter>,
iter: I,
}
impl<I, E, O2, U> Iterator for FlattenOk<I, U>
where
I: Iterator<Item = Result<U, E>>,
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(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 FlattenErr<I, U: IntoIterator> {
frontiter: Option<<U as IntoIterator>::IntoIter>,
iter: I,
}
impl<I, O, E2, U> Iterator for FlattenErr<I, U>
where
I: Iterator<Item = Result<O, 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(e.into_iter());
}
Some(Ok(o)) => return Some(Ok(o)),
}
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}