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