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1 | use std::cmp::Ordering::{Equal, Greater, Less}; |
2 | use super::size_hint; | |
3 | use std::iter::Fuse; | |
4 | ||
5 | use either_or_both::EitherOrBoth; | |
6 | ||
7 | // ZipLongest originally written by SimonSapin, | |
8 | // and dedicated to itertools https://github.com/rust-lang/rust/pull/19283 | |
9 | ||
10 | /// An iterator which iterates two other iterators simultaneously | |
11 | /// | |
12 | /// This iterator is *fused*. | |
13 | /// | |
14 | /// See [`.zip_longest()`](../trait.Itertools.html#method.zip_longest) for more information. | |
15 | #[derive(Clone, Debug)] | |
16 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] | |
17 | pub struct ZipLongest<T, U> { | |
18 | a: Fuse<T>, | |
19 | b: Fuse<U>, | |
20 | } | |
21 | ||
22 | /// Create a new `ZipLongest` iterator. | |
23 | pub fn zip_longest<T, U>(a: T, b: U) -> ZipLongest<T, U> | |
24 | where T: Iterator, | |
25 | U: Iterator | |
26 | { | |
27 | ZipLongest { | |
28 | a: a.fuse(), | |
29 | b: b.fuse(), | |
30 | } | |
31 | } | |
32 | ||
33 | impl<T, U> Iterator for ZipLongest<T, U> | |
34 | where T: Iterator, | |
35 | U: Iterator | |
36 | { | |
37 | type Item = EitherOrBoth<T::Item, U::Item>; | |
38 | ||
39 | #[inline] | |
40 | fn next(&mut self) -> Option<Self::Item> { | |
41 | match (self.a.next(), self.b.next()) { | |
42 | (None, None) => None, | |
43 | (Some(a), None) => Some(EitherOrBoth::Left(a)), | |
44 | (None, Some(b)) => Some(EitherOrBoth::Right(b)), | |
45 | (Some(a), Some(b)) => Some(EitherOrBoth::Both(a, b)), | |
46 | } | |
47 | } | |
48 | ||
49 | #[inline] | |
50 | fn size_hint(&self) -> (usize, Option<usize>) { | |
51 | size_hint::max(self.a.size_hint(), self.b.size_hint()) | |
52 | } | |
53 | } | |
54 | ||
55 | impl<T, U> DoubleEndedIterator for ZipLongest<T, U> | |
56 | where T: DoubleEndedIterator + ExactSizeIterator, | |
57 | U: DoubleEndedIterator + ExactSizeIterator | |
58 | { | |
59 | #[inline] | |
60 | fn next_back(&mut self) -> Option<Self::Item> { | |
61 | match self.a.len().cmp(&self.b.len()) { | |
62 | Equal => match (self.a.next_back(), self.b.next_back()) { | |
63 | (None, None) => None, | |
64 | (Some(a), Some(b)) => Some(EitherOrBoth::Both(a, b)), | |
65 | // These can only happen if .len() is inconsistent with .next_back() | |
66 | (Some(a), None) => Some(EitherOrBoth::Left(a)), | |
67 | (None, Some(b)) => Some(EitherOrBoth::Right(b)), | |
68 | }, | |
69 | Greater => self.a.next_back().map(EitherOrBoth::Left), | |
70 | Less => self.b.next_back().map(EitherOrBoth::Right), | |
71 | } | |
72 | } | |
73 | } | |
74 | ||
75 | impl<T, U> ExactSizeIterator for ZipLongest<T, U> | |
76 | where T: ExactSizeIterator, | |
77 | U: ExactSizeIterator | |
78 | {} |