itertools/
ziptuple.rs

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);
itertools/ziptuple.rs

itertools/
ziptuple.rs
