1 use crate::{iter::FusedIterator, ops::Try};
3 /// An iterator that repeats endlessly.
5 /// This `struct` is created by the [`cycle`] method on [`Iterator`]. See its
6 /// documentation for more.
8 /// [`cycle`]: Iterator::cycle
9 /// [`Iterator`]: trait.Iterator.html
10 #[derive(Clone, Debug)]
11 #[must_use = "iterators are lazy and do nothing unless consumed"]
12 #[stable(feature = "rust1", since = "1.0.0")]
18 impl<I: Clone> Cycle<I> {
19 pub(in crate::iter) fn new(iter: I) -> Cycle<I> {
20 Cycle { orig: iter.clone(), iter }
24 #[stable(feature = "rust1", since = "1.0.0")]
25 impl<I> Iterator for Cycle<I>
29 type Item = <I as Iterator>::Item;
32 fn next(&mut self) -> Option<<I as Iterator>::Item> {
33 match self.iter.next() {
35 self.iter = self.orig.clone();
43 fn size_hint(&self) -> (usize, Option<usize>) {
44 // the cycle iterator is either empty or infinite
45 match self.orig.size_hint() {
46 sz @ (0, Some(0)) => sz,
48 _ => (usize::MAX, None),
53 fn try_fold<Acc, F, R>(&mut self, mut acc: Acc, mut f: F) -> R
55 F: FnMut(Acc, Self::Item) -> R,
58 // fully iterate the current iterator. this is necessary because
59 // `self.iter` may be empty even when `self.orig` isn't
60 acc = self.iter.try_fold(acc, &mut f)?;
61 self.iter = self.orig.clone();
63 // complete a full cycle, keeping track of whether the cycled
64 // iterator is empty or not. we need to return early in case
65 // of an empty iterator to prevent an infinite loop
66 let mut is_empty = true;
67 acc = self.iter.try_fold(acc, |acc, x| {
77 self.iter = self.orig.clone();
78 acc = self.iter.try_fold(acc, &mut f)?;
82 // No `fold` override, because `fold` doesn't make much sense for `Cycle`,
83 // and we can't do anything better than the default.
86 #[stable(feature = "fused", since = "1.26.0")]
87 impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}