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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /library/core/src/iter/adapters/cycle.rs | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'library/core/src/iter/adapters/cycle.rs')
-rw-r--r-- | library/core/src/iter/adapters/cycle.rs | 108 |
1 files changed, 108 insertions, 0 deletions
diff --git a/library/core/src/iter/adapters/cycle.rs b/library/core/src/iter/adapters/cycle.rs new file mode 100644 index 000000000..02b593907 --- /dev/null +++ b/library/core/src/iter/adapters/cycle.rs @@ -0,0 +1,108 @@ +use crate::{iter::FusedIterator, ops::Try}; + +/// An iterator that repeats endlessly. +/// +/// This `struct` is created by the [`cycle`] method on [`Iterator`]. See its +/// documentation for more. +/// +/// [`cycle`]: Iterator::cycle +/// [`Iterator`]: trait.Iterator.html +#[derive(Clone, Debug)] +#[must_use = "iterators are lazy and do nothing unless consumed"] +#[stable(feature = "rust1", since = "1.0.0")] +pub struct Cycle<I> { + orig: I, + iter: I, +} + +impl<I: Clone> Cycle<I> { + pub(in crate::iter) fn new(iter: I) -> Cycle<I> { + Cycle { orig: iter.clone(), iter } + } +} + +#[stable(feature = "rust1", since = "1.0.0")] +impl<I> Iterator for Cycle<I> +where + I: Clone + Iterator, +{ + type Item = <I as Iterator>::Item; + + #[inline] + fn next(&mut self) -> Option<<I as Iterator>::Item> { + match self.iter.next() { + None => { + self.iter = self.orig.clone(); + self.iter.next() + } + y => y, + } + } + + #[inline] + fn size_hint(&self) -> (usize, Option<usize>) { + // the cycle iterator is either empty or infinite + match self.orig.size_hint() { + sz @ (0, Some(0)) => sz, + (0, _) => (0, None), + _ => (usize::MAX, None), + } + } + + #[inline] + fn try_fold<Acc, F, R>(&mut self, mut acc: Acc, mut f: F) -> R + where + F: FnMut(Acc, Self::Item) -> R, + R: Try<Output = Acc>, + { + // fully iterate the current iterator. this is necessary because + // `self.iter` may be empty even when `self.orig` isn't + acc = self.iter.try_fold(acc, &mut f)?; + self.iter = self.orig.clone(); + + // complete a full cycle, keeping track of whether the cycled + // iterator is empty or not. we need to return early in case + // of an empty iterator to prevent an infinite loop + let mut is_empty = true; + acc = self.iter.try_fold(acc, |acc, x| { + is_empty = false; + f(acc, x) + })?; + + if is_empty { + return try { acc }; + } + + loop { + self.iter = self.orig.clone(); + acc = self.iter.try_fold(acc, &mut f)?; + } + } + + #[inline] + #[rustc_inherit_overflow_checks] + fn advance_by(&mut self, n: usize) -> Result<(), usize> { + let mut rem = n; + match self.iter.advance_by(rem) { + ret @ Ok(_) => return ret, + Err(advanced) => rem -= advanced, + } + + while rem > 0 { + self.iter = self.orig.clone(); + match self.iter.advance_by(rem) { + ret @ Ok(_) => return ret, + Err(0) => return Err(n - rem), + Err(advanced) => rem -= advanced, + } + } + + Ok(()) + } + + // No `fold` override, because `fold` doesn't make much sense for `Cycle`, + // and we can't do anything better than the default. +} + +#[stable(feature = "fused", since = "1.26.0")] +impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {} |