core/iter/adapters/
cycle.rsuse crate::iter::FusedIterator;
use crate::num::NonZero;
use crate::ops::Try;
#[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>) {
        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>,
    {
        acc = self.iter.try_fold(acc, &mut f)?;
        self.iter = self.orig.clone();
        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<(), NonZero<usize>> {
        let mut n = match self.iter.advance_by(n) {
            Ok(()) => return Ok(()),
            Err(rem) => rem.get(),
        };
        while n > 0 {
            self.iter = self.orig.clone();
            n = match self.iter.advance_by(n) {
                Ok(()) => return Ok(()),
                e @ Err(rem) if rem.get() == n => return e,
                Err(rem) => rem.get(),
            };
        }
        NonZero::new(n).map_or(Ok(()), Err)
    }
    }
#[stable(feature = "fused", since = "1.26.0")]
impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}