interleave.rs

fn interleave<I>(its: Vec<I>) -> Interleave<I> {
    Interleave { its: its.into_iter().collect() }
}

struct Interleave<I> {
    its: std::collections::VecDeque<I>,
}

impl<I: Iterator> Iterator for Interleave<I> {
    type Item = I::Item;

    fn next(&mut self) -> Option<I::Item> {
        loop {
            let mut it = self.its.pop_front()?;
            if let Some(elem) = it.next() {
                self.its.push_back(it);
                return Some(elem);
            }
        }
    }
}