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use std::cmp::Ordering::{Equal, Greater, Less};
use super::size_hint;
use std::iter::{Fuse, FusedIterator};
use crate::either_or_both::EitherOrBoth;
// ZipLongest originally written by SimonSapin,
// and dedicated to itertools https://github.com/rust-lang/rust/pull/19283
/// An iterator which iterates two other iterators simultaneously
///
/// This iterator is *fused*.
///
/// See [`.zip_longest()`](crate::Itertools::zip_longest) for more information.
#[derive(Clone, Debug)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct ZipLongest<T, U> {
a: Fuse<T>,
b: Fuse<U>,
}
/// Create a new `ZipLongest` iterator.
pub fn zip_longest<T, U>(a: T, b: U) -> ZipLongest<T, U>
where T: Iterator,
U: Iterator
{
ZipLongest {
a: a.fuse(),
b: b.fuse(),
}
}
impl<T, U> Iterator for ZipLongest<T, U>
where T: Iterator,
U: Iterator
{
type Item = EitherOrBoth<T::Item, U::Item>;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
match (self.a.next(), self.b.next()) {
(None, None) => None,
(Some(a), None) => Some(EitherOrBoth::Left(a)),
(None, Some(b)) => Some(EitherOrBoth::Right(b)),
(Some(a), Some(b)) => Some(EitherOrBoth::Both(a, b)),
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
size_hint::max(self.a.size_hint(), self.b.size_hint())
}
}
impl<T, U> DoubleEndedIterator for ZipLongest<T, U>
where T: DoubleEndedIterator + ExactSizeIterator,
U: DoubleEndedIterator + ExactSizeIterator
{
#[inline]
fn next_back(&mut self) -> Option<Self::Item> {
match self.a.len().cmp(&self.b.len()) {
Equal => match (self.a.next_back(), self.b.next_back()) {
(None, None) => None,
(Some(a), Some(b)) => Some(EitherOrBoth::Both(a, b)),
// These can only happen if .len() is inconsistent with .next_back()
(Some(a), None) => Some(EitherOrBoth::Left(a)),
(None, Some(b)) => Some(EitherOrBoth::Right(b)),
},
Greater => self.a.next_back().map(EitherOrBoth::Left),
Less => self.b.next_back().map(EitherOrBoth::Right),
}
}
}
impl<T, U> ExactSizeIterator for ZipLongest<T, U>
where T: ExactSizeIterator,
U: ExactSizeIterator
{}
impl<T, U> FusedIterator for ZipLongest<T, U>
where T: Iterator,
U: Iterator
{}
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