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527: add .flatten_ok() r=jswrenn a=vadixidav Closes #522 Co-authored-by: Geordon Worley <vadixidav@gmail.com>
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use crate::size_hint; | ||
use std::{ | ||
fmt, | ||
iter::{DoubleEndedIterator, FusedIterator}, | ||
}; | ||
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pub fn flatten_ok<I, T, E>(iter: I) -> FlattenOk<I, T, E> | ||
where | ||
I: Iterator<Item = Result<T, E>>, | ||
T: IntoIterator, | ||
{ | ||
FlattenOk { | ||
iter, | ||
inner_front: None, | ||
inner_back: None, | ||
} | ||
} | ||
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/// An iterator adaptor that flattens `Result::Ok` values and | ||
/// allows `Result::Err` values through unchanged. | ||
/// | ||
/// See [`.flatten_ok()`](crate::Itertools::flatten_ok) for more information. | ||
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"] | ||
pub struct FlattenOk<I, T, E> | ||
where | ||
I: Iterator<Item = Result<T, E>>, | ||
T: IntoIterator, | ||
{ | ||
iter: I, | ||
inner_front: Option<T::IntoIter>, | ||
inner_back: Option<T::IntoIter>, | ||
} | ||
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impl<I, T, E> Iterator for FlattenOk<I, T, E> | ||
where | ||
I: Iterator<Item = Result<T, E>>, | ||
T: IntoIterator, | ||
{ | ||
type Item = Result<T::Item, E>; | ||
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fn next(&mut self) -> Option<Self::Item> { | ||
loop { | ||
// Handle the front inner iterator. | ||
if let Some(inner) = &mut self.inner_front { | ||
if let Some(item) = inner.next() { | ||
return Some(Ok(item)); | ||
} else { | ||
// This is necessary for the iterator to implement `FusedIterator` | ||
// with only the orginal iterator being fused. | ||
self.inner_front = None; | ||
} | ||
} | ||
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match self.iter.next() { | ||
Some(Ok(ok)) => self.inner_front = Some(ok.into_iter()), | ||
Some(Err(e)) => return Some(Err(e)), | ||
None => { | ||
// Handle the back inner iterator. | ||
if let Some(inner) = &mut self.inner_back { | ||
if let Some(item) = inner.next() { | ||
return Some(Ok(item)); | ||
} else { | ||
// This is necessary for the iterator to implement `FusedIterator` | ||
// with only the orginal iterator being fused. | ||
self.inner_back = None; | ||
} | ||
} else { | ||
return None; | ||
} | ||
} | ||
} | ||
} | ||
} | ||
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fn size_hint(&self) -> (usize, Option<usize>) { | ||
let inner_hint = |inner: &Option<T::IntoIter>| { | ||
inner | ||
.as_ref() | ||
.map(Iterator::size_hint) | ||
.unwrap_or((0, Some(0))) | ||
}; | ||
let inner_front = inner_hint(&self.inner_front); | ||
let inner_back = inner_hint(&self.inner_back); | ||
// The outer iterator `Ok` case could be (0, None) as we don't know its size_hint yet. | ||
let outer = match self.iter.size_hint() { | ||
(0, Some(0)) => (0, Some(0)), | ||
_ => (0, None), | ||
}; | ||
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size_hint::add(size_hint::add(inner_front, inner_back), outer) | ||
} | ||
} | ||
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impl<I, T, E> DoubleEndedIterator for FlattenOk<I, T, E> | ||
where | ||
I: DoubleEndedIterator<Item = Result<T, E>>, | ||
T: IntoIterator, | ||
T::IntoIter: DoubleEndedIterator, | ||
{ | ||
fn next_back(&mut self) -> Option<Self::Item> { | ||
loop { | ||
// Handle the back inner iterator. | ||
if let Some(inner) = &mut self.inner_back { | ||
if let Some(item) = inner.next_back() { | ||
return Some(Ok(item)); | ||
} else { | ||
// This is necessary for the iterator to implement `FusedIterator` | ||
// with only the orginal iterator being fused. | ||
self.inner_back = None; | ||
} | ||
} | ||
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match self.iter.next_back() { | ||
Some(Ok(ok)) => self.inner_back = Some(ok.into_iter()), | ||
Some(Err(e)) => return Some(Err(e)), | ||
None => { | ||
// Handle the front inner iterator. | ||
if let Some(inner) = &mut self.inner_front { | ||
if let Some(item) = inner.next_back() { | ||
return Some(Ok(item)); | ||
} else { | ||
// This is necessary for the iterator to implement `FusedIterator` | ||
// with only the orginal iterator being fused. | ||
self.inner_front = None; | ||
} | ||
} else { | ||
return None; | ||
} | ||
} | ||
} | ||
} | ||
} | ||
} | ||
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impl<I, T, E> Clone for FlattenOk<I, T, E> | ||
where | ||
I: Iterator<Item = Result<T, E>> + Clone, | ||
T: IntoIterator, | ||
T::IntoIter: Clone, | ||
{ | ||
#[inline] | ||
clone_fields!(iter, inner_front, inner_back); | ||
} | ||
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impl<I, T, E> fmt::Debug for FlattenOk<I, T, E> | ||
where | ||
I: Iterator<Item = Result<T, E>> + fmt::Debug, | ||
T: IntoIterator, | ||
T::IntoIter: fmt::Debug, | ||
{ | ||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
f.debug_struct("FlattenOk") | ||
.field("iter", &self.iter) | ||
.field("inner_front", &self.inner_front) | ||
.field("inner_back", &self.inner_back) | ||
.finish() | ||
} | ||
} | ||
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/// Only the iterator being flattened needs to implement [`FusedIterator`]. | ||
impl<I, T, E> FusedIterator for FlattenOk<I, T, E> | ||
where | ||
I: FusedIterator<Item = Result<T, E>>, | ||
T: IntoIterator, | ||
{ | ||
} |
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,76 @@ | ||
use itertools::{assert_equal, Itertools}; | ||
use std::{ops::Range, vec::IntoIter}; | ||
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fn mix_data() -> IntoIter<Result<Range<i32>, bool>> { | ||
vec![Ok(0..2), Err(false), Ok(2..4), Err(true), Ok(4..6)].into_iter() | ||
} | ||
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fn ok_data() -> IntoIter<Result<Range<i32>, bool>> { | ||
vec![Ok(0..2), Ok(2..4), Ok(4..6)].into_iter() | ||
} | ||
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#[test] | ||
fn flatten_ok_mixed_expected_forward() { | ||
assert_equal( | ||
mix_data().flatten_ok(), | ||
vec![ | ||
Ok(0), | ||
Ok(1), | ||
Err(false), | ||
Ok(2), | ||
Ok(3), | ||
Err(true), | ||
Ok(4), | ||
Ok(5), | ||
], | ||
); | ||
} | ||
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#[test] | ||
fn flatten_ok_mixed_expected_reverse() { | ||
assert_equal( | ||
mix_data().flatten_ok().rev(), | ||
vec![ | ||
Ok(5), | ||
Ok(4), | ||
Err(true), | ||
Ok(3), | ||
Ok(2), | ||
Err(false), | ||
Ok(1), | ||
Ok(0), | ||
], | ||
); | ||
} | ||
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#[test] | ||
fn flatten_ok_collect_mixed_forward() { | ||
assert_eq!( | ||
mix_data().flatten_ok().collect::<Result<Vec<_>, _>>(), | ||
Err(false) | ||
); | ||
} | ||
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#[test] | ||
fn flatten_ok_collect_mixed_reverse() { | ||
assert_eq!( | ||
mix_data().flatten_ok().rev().collect::<Result<Vec<_>, _>>(), | ||
Err(true) | ||
); | ||
} | ||
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#[test] | ||
fn flatten_ok_collect_ok_forward() { | ||
assert_eq!( | ||
ok_data().flatten_ok().collect::<Result<Vec<_>, _>>(), | ||
Ok((0..6).collect()) | ||
); | ||
} | ||
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#[test] | ||
fn flatten_ok_collect_ok_reverse() { | ||
assert_eq!( | ||
ok_data().flatten_ok().rev().collect::<Result<Vec<_>, _>>(), | ||
Ok((0..6).rev().collect()) | ||
); | ||
} |