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    use crate::iter::{FusedIterator, TrustedLen};
    use crate::ops::Try;

    /// A double-ended iterator with the direction inverted.
    ///
    /// This `struct` is created by the [`rev`] method on [`Iterator`]. See its
    /// documentation for more.
    ///
    /// [`rev`]: Iterator::rev
    /// [`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 Rev<T> {
        iter: T,
    }

    impl<T> Rev<T> {
        pub(in crate::iter) fn new(iter: T) -> Rev<T> {
            Rev { iter }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<I> Iterator for Rev<I>
    where
        I: DoubleEndedIterator,
    {
        type Item = <I as Iterator>::Item;

        #[inline]
        fn next(&mut self) -> Option<<I as Iterator>::Item> {
            self.iter.next_back()
        }
        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            self.iter.size_hint()
        }

        #[inline]
        fn advance_by(&mut self, n: usize) -> Result<(), usize> {
            self.iter.advance_back_by(n)
        }

        #[inline]
        fn nth(&mut self, n: usize) -> Option<<I as Iterator>::Item> {
            self.iter.nth_back(n)
        }

        fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
        where
            Self: Sized,
            F: FnMut(B, Self::Item) -> R,
            R: Try<Ok = B>,
        {
            self.iter.try_rfold(init, f)
        }

        fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
        where
            F: FnMut(Acc, Self::Item) -> Acc,
        {
            self.iter.rfold(init, f)
        }

        #[inline]
        fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
        where
            P: FnMut(&Self::Item) -> bool,
        {
            self.iter.rfind(predicate)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<I> DoubleEndedIterator for Rev<I>
    where
        I: DoubleEndedIterator,
    {
        #[inline]
        fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
            self.iter.next()
        }

        #[inline]
        fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
            self.iter.advance_by(n)
        }

        #[inline]
        fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item> {
            self.iter.nth(n)
        }

        fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
        where
            Self: Sized,
            F: FnMut(B, Self::Item) -> R,
            R: Try<Ok = B>,
        {
            self.iter.try_fold(init, f)
        }

        fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
        where
            F: FnMut(Acc, Self::Item) -> Acc,
        {
            self.iter.fold(init, f)
        }

        fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
        where
            P: FnMut(&Self::Item) -> bool,
        {
            self.iter.find(predicate)
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<I> ExactSizeIterator for Rev<I>
    where
        I: ExactSizeIterator + DoubleEndedIterator,
    {
        fn len(&self) -> usize {
            self.iter.len()
        }

        fn is_empty(&self) -> bool {
            self.iter.is_empty()
        }
    }

    #[stable(feature = "fused", since = "1.26.0")]
    impl<I> FusedIterator for Rev<I> where I: FusedIterator + DoubleEndedIterator {}

    #[unstable(feature = "trusted_len", issue = "37572")]
    unsafe impl<I> TrustedLen for Rev<I> where I: TrustedLen + DoubleEndedIterator {}