opt_iter.rs

struct OptionIter<I> {
    iter: Option<I>,
}

impl<I> Iterator for OptionIter<I>
where
    I: Iterator,
{
    type Item = Option<I::Item>;

    fn next(&mut self) -> Option<Self::Item> {
        match self.iter {
            None => return Some(None),
            Some(ref mut iter) => Some(iter.next()),
        }
    }
}