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 macro 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!()`] 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/// ```
39/// [`izip!()`]: crate::izip
40pub fn multizip<T, U>(t: U) -> Zip<T>
41where
42 Zip<T>: From<U> + Iterator,
43{
44 Zip::from(t)
45}
46
47macro_rules! impl_zip_iter {
48 ($($B:ident),*) => (
49 #[allow(non_snake_case)]
50 impl<$($B: IntoIterator),*> From<($($B,)*)> for Zip<($($B::IntoIter,)*)> {
51 fn from(t: ($($B,)*)) -> Self {
52 let ($($B,)*) = t;
53 Zip { t: ($($B.into_iter(),)*) }
54 }
55 }
56
57 #[allow(non_snake_case)]
58 #[allow(unused_assignments)]
59 impl<$($B),*> Iterator for Zip<($($B,)*)>
60 where
61 $(
62 $B: Iterator,
63 )*
64 {
65 type Item = ($($B::Item,)*);
66
67 fn next(&mut self) -> Option<Self::Item>
68 {
69 let ($(ref mut $B,)*) = self.t;
70
71 // NOTE: Just like iter::Zip, we check the iterators
72 // for None in order. We may finish unevenly (some
73 // iterators gave n + 1 elements, some only n).
74 $(
75 let $B = match $B.next() {
76 None => return None,
77 Some(elt) => elt
78 };
79 )*
80 Some(($($B,)*))
81 }
82
83 fn size_hint(&self) -> (usize, Option<usize>)
84 {
85 let sh = (::std::usize::MAX, None);
86 let ($(ref $B,)*) = self.t;
87 $(
88 let sh = size_hint::min($B.size_hint(), sh);
89 )*
90 sh
91 }
92 }
93
94 #[allow(non_snake_case)]
95 impl<$($B),*> ExactSizeIterator for Zip<($($B,)*)> where
96 $(
97 $B: ExactSizeIterator,
98 )*
99 { }
100
101 #[allow(non_snake_case)]
102 impl<$($B),*> DoubleEndedIterator for Zip<($($B,)*)> where
103 $(
104 $B: DoubleEndedIterator + ExactSizeIterator,
105 )*
106 {
107 #[inline]
108 fn next_back(&mut self) -> Option<Self::Item> {
109 let ($(ref mut $B,)*) = self.t;
110 let size = *[$( $B.len(), )*].iter().min().unwrap();
111
112 $(
113 if $B.len() != size {
114 for _ in 0..$B.len() - size { $B.next_back(); }
115 }
116 )*
117
118 match ($($B.next_back(),)*) {
119 ($(Some($B),)*) => Some(($($B,)*)),
120 _ => None,
121 }
122 }
123 }
124 );
125}
126
127impl_zip_iter!(A);
128impl_zip_iter!(A, B);
129impl_zip_iter!(A, B, C);
130impl_zip_iter!(A, B, C, D);
131impl_zip_iter!(A, B, C, D, E);
132impl_zip_iter!(A, B, C, D, E, F);
133impl_zip_iter!(A, B, C, D, E, F, G);
134impl_zip_iter!(A, B, C, D, E, F, G, H);
135impl_zip_iter!(A, B, C, D, E, F, G, H, I);
136impl_zip_iter!(A, B, C, D, E, F, G, H, I, J);
137impl_zip_iter!(A, B, C, D, E, F, G, H, I, J, K);
138impl_zip_iter!(A, B, C, D, E, F, G, H, I, J, K, L);
139