Trait method
<either::Either as DoubleEndedIterator>::next_back
impl<L, R> DoubleEndedIterator for super::Either<L, R> where L: DoubleEndedIterator, R: DoubleEndedIterator<Item = <L as core::iter::traits::iterator::Iterator>::Item>
pub fn next_back(self: &mut Self) -> Option<<Self as core::iter::traits::iterator::Iterator>::Item>