1 | use crate::iter::FusedIterator; |
2 | use crate::num::NonZero; |
3 | use crate::ops::Try; |
4 | |
5 | /// An iterator that repeats endlessly. |
6 | /// |
7 | /// This `struct` is created by the [`cycle`] method on [`Iterator`]. See its |
8 | /// documentation for more. |
9 | /// |
10 | /// [`cycle`]: Iterator::cycle |
11 | /// [`Iterator`]: trait.Iterator.html |
12 | #[derive (Clone, Debug)] |
13 | #[must_use = "iterators are lazy and do nothing unless consumed" ] |
14 | #[stable (feature = "rust1" , since = "1.0.0" )] |
15 | pub struct Cycle<I> { |
16 | orig: I, |
17 | iter: I, |
18 | } |
19 | |
20 | impl<I: Clone> Cycle<I> { |
21 | pub(in crate::iter) fn new(iter: I) -> Cycle<I> { |
22 | Cycle { orig: iter.clone(), iter } |
23 | } |
24 | } |
25 | |
26 | #[stable (feature = "rust1" , since = "1.0.0" )] |
27 | impl<I> Iterator for Cycle<I> |
28 | where |
29 | I: Clone + Iterator, |
30 | { |
31 | type Item = <I as Iterator>::Item; |
32 | |
33 | #[inline ] |
34 | fn next(&mut self) -> Option<<I as Iterator>::Item> { |
35 | match self.iter.next() { |
36 | None => { |
37 | self.iter = self.orig.clone(); |
38 | self.iter.next() |
39 | } |
40 | y => y, |
41 | } |
42 | } |
43 | |
44 | #[inline ] |
45 | fn size_hint(&self) -> (usize, Option<usize>) { |
46 | // the cycle iterator is either empty or infinite |
47 | match self.orig.size_hint() { |
48 | sz @ (0, Some(0)) => sz, |
49 | (0, _) => (0, None), |
50 | _ => (usize::MAX, None), |
51 | } |
52 | } |
53 | |
54 | #[inline ] |
55 | fn try_fold<Acc, F, R>(&mut self, mut acc: Acc, mut f: F) -> R |
56 | where |
57 | F: FnMut(Acc, Self::Item) -> R, |
58 | R: Try<Output = Acc>, |
59 | { |
60 | // fully iterate the current iterator. this is necessary because |
61 | // `self.iter` may be empty even when `self.orig` isn't |
62 | acc = self.iter.try_fold(acc, &mut f)?; |
63 | self.iter = self.orig.clone(); |
64 | |
65 | // complete a full cycle, keeping track of whether the cycled |
66 | // iterator is empty or not. we need to return early in case |
67 | // of an empty iterator to prevent an infinite loop |
68 | let mut is_empty = true; |
69 | acc = self.iter.try_fold(acc, |acc, x| { |
70 | is_empty = false; |
71 | f(acc, x) |
72 | })?; |
73 | |
74 | if is_empty { |
75 | return try { acc }; |
76 | } |
77 | |
78 | loop { |
79 | self.iter = self.orig.clone(); |
80 | acc = self.iter.try_fold(acc, &mut f)?; |
81 | } |
82 | } |
83 | |
84 | #[inline ] |
85 | #[rustc_inherit_overflow_checks ] |
86 | fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> { |
87 | let mut n = match self.iter.advance_by(n) { |
88 | Ok(()) => return Ok(()), |
89 | Err(rem) => rem.get(), |
90 | }; |
91 | |
92 | while n > 0 { |
93 | self.iter = self.orig.clone(); |
94 | n = match self.iter.advance_by(n) { |
95 | Ok(()) => return Ok(()), |
96 | e @ Err(rem) if rem.get() == n => return e, |
97 | Err(rem) => rem.get(), |
98 | }; |
99 | } |
100 | |
101 | NonZero::new(n).map_or(Ok(()), Err) |
102 | } |
103 | |
104 | // No `fold` override, because `fold` doesn't make much sense for `Cycle`, |
105 | // and we can't do anything better than the default. |
106 | } |
107 | |
108 | #[stable (feature = "fused" , since = "1.26.0" )] |
109 | impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {} |
110 | |