1 use 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"]
6 pub 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 /// ```
multizip<T, U>(t: U) -> Zip<T> where Zip<T>: From<U>, Zip<T>: Iterator,39 pub fn multizip<T, U>(t: U) -> Zip<T>
40 where Zip<T>: From<U>,
41 Zip<T>: Iterator,
42 {
43 Zip::from(t)
44 }
45
46 macro_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 $B.next() {
75 None => return None,
76 Some(elt) => elt
77 };
78 )*
79 Some(($($B,)*))
80 }
81
82 fn size_hint(&self) -> (usize, Option<usize>)
83 {
84 let sh = (::std::usize::MAX, None);
85 let ($(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
126 impl_zip_iter!(A);
127 impl_zip_iter!(A, B);
128 impl_zip_iter!(A, B, C);
129 impl_zip_iter!(A, B, C, D);
130 impl_zip_iter!(A, B, C, D, E);
131 impl_zip_iter!(A, B, C, D, E, F);
132 impl_zip_iter!(A, B, C, D, E, F, G);
133 impl_zip_iter!(A, B, C, D, E, F, G, H);
134 impl_zip_iter!(A, B, C, D, E, F, G, H, I);
135 impl_zip_iter!(A, B, C, D, E, F, G, H, I, J);
136 impl_zip_iter!(A, B, C, D, E, F, G, H, I, J, K);
137 impl_zip_iter!(A, B, C, D, E, F, G, H, I, J, K, L);
138