/// An iterator that could be either of two iterators.
#[derive(Clone, Debug)]
pub enum EitherIter<A, B> {
    A(A),
    B(B),
}

impl<A, B, T> Iterator for EitherIter<A, B>
where
    A: Iterator<Item = T>,
    B: Iterator<Item = T>,
{
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        match self {
            EitherIter::A(iter) => iter.next(),
            EitherIter::B(iter) => iter.next(),
        }
    }
}