fn next(&mut self) -> Option<&'a T> {
        match &mut self.inner {
            IntersectionInner::Stitch { a, b } => {
                let mut a_next = a.next()?;
                let mut b_next = b.next()?;
                loop {
                    match a_next.cmp(b_next) {
                        Less => a_next = a.next()?,
                        Greater => b_next = b.next()?,
                        Equal => return Some(a_next),
                    }
                }
            }
            IntersectionInner::Search { small_iter, large_set } => loop {
                let small_next = small_iter.next()?;
                if large_set.contains(&small_next) {
                    return Some(small_next);
                }
            },
            IntersectionInner::Answer(answer) => answer.take(),
        }
    }
Temporarily takes out another, immutable equival
benchmarks/haystacks/code/rust-library.rs