1use super::size_hint;
2
3/// See [`multizip`] for more information.
4#[derive(Clone, Debug)]
5#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
6pub struct Zip<T> {
7 t: T,
8}
9
10/// An iterator that generalizes `.zip()` and allows running multiple iterators in lockstep.
11///
12/// The iterator `Zip<(I, J, ..., M)>` is formed from a tuple of iterators (or values that
13/// implement [`IntoIterator`]) and yields elements
14/// until any of the subiterators yields `None`.
15///
16/// The iterator element type is a tuple like like `(A, B, ..., E)` where `A` to `E` are the
17/// element types of the subiterator.
18///
19/// **Note:** The result of this function is a value of a named type (`Zip<(I, J,
20/// ..)>` of each component iterator `I, J, ...`) if each component iterator is
21/// nameable.
22///
23/// Prefer [`izip!()`](crate::izip) over `multizip` for the performance benefits of using the
24/// standard library `.zip()`. Prefer `multizip` if a nameable type is needed.
25///
26/// ```
27/// use itertools::multizip;
28///
29/// // iterate over three sequences side-by-side
30/// let mut results = [0, 0, 0, 0];
31/// let inputs = [3, 7, 9, 6];
32///
33/// for (r, index, input) in multizip((&mut results, 0..10, &inputs)) {
34/// *r = index * 10 + input;
35/// }
36///
37/// assert_eq!(results, [0 + 3, 10 + 7, 29, 36]);
38/// ```
39pub fn multizip<T, U>(t: U) -> Zip<T>
40where
41 Zip<T>: From<U> + Iterator,
42{
43 Zip::from(t)
44}
45
46macro_rules! impl_zip_iter {
47 ($($B:ident),*) => (
48 #[allow(non_snake_case)]
49 impl<$($B: IntoIterator),*> From<($($B,)*)> for Zip<($($B::IntoIter,)*)> {
50 fn from(t: ($($B,)*)) -> Self {
51 let ($($B,)*) = t;
52 Zip { t: ($($B.into_iter(),)*) }
53 }
54 }
55
56 #[allow(non_snake_case)]
57 #[allow(unused_assignments)]
58 impl<$($B),*> Iterator for Zip<($($B,)*)>
59 where
60 $(
61 $B: Iterator,
62 )*
63 {
64 type Item = ($($B::Item,)*);
65
66 fn next(&mut self) -> Option<Self::Item>
67 {
68 let ($(ref mut $B,)*) = self.t;
69
70 // NOTE: Just like iter::Zip, we check the iterators
71 // for None in order. We may finish unevenly (some
72 // iterators gave n + 1 elements, some only n).
73 $(
74 let $B = match $B.next() {
75 None => return None,
76 Some(elt) => elt
77 };
78 )*
79 Some(($($B,)*))
80 }
81
82 fn size_hint(&self) -> (usize, Option<usize>)
83 {
84 let sh = (usize::MAX, None);
85 let ($(ref $B,)*) = self.t;
86 $(
87 let sh = size_hint::min($B.size_hint(), sh);
88 )*
89 sh
90 }
91 }
92
93 #[allow(non_snake_case)]
94 impl<$($B),*> ExactSizeIterator for Zip<($($B,)*)> where
95 $(
96 $B: ExactSizeIterator,
97 )*
98 { }
99
100 #[allow(non_snake_case)]
101 impl<$($B),*> DoubleEndedIterator for Zip<($($B,)*)> where
102 $(
103 $B: DoubleEndedIterator + ExactSizeIterator,
104 )*
105 {
106 #[inline]
107 fn next_back(&mut self) -> Option<Self::Item> {
108 let ($(ref mut $B,)*) = self.t;
109 let size = *[$( $B.len(), )*].iter().min().unwrap();
110
111 $(
112 if $B.len() != size {
113 for _ in 0..$B.len() - size { $B.next_back(); }
114 }
115 )*
116
117 match ($($B.next_back(),)*) {
118 ($(Some($B),)*) => Some(($($B,)*)),
119 _ => None,
120 }
121 }
122 }
123 );
124}
125
126impl_zip_iter!(A);
127impl_zip_iter!(A, B);
128impl_zip_iter!(A, B, C);
129impl_zip_iter!(A, B, C, D);
130impl_zip_iter!(A, B, C, D, E);
131impl_zip_iter!(A, B, C, D, E, F);
132impl_zip_iter!(A, B, C, D, E, F, G);
133impl_zip_iter!(A, B, C, D, E, F, G, H);
134impl_zip_iter!(A, B, C, D, E, F, G, H, I);
135impl_zip_iter!(A, B, C, D, E, F, G, H, I, J);
136impl_zip_iter!(A, B, C, D, E, F, G, H, I, J, K);
137impl_zip_iter!(A, B, C, D, E, F, G, H, I, J, K, L);
138