use std::marker;

#[derive(Debug)]
struct Key<T> {
    idx: u32,
    version: u32,
    _marker: marker::PhantomData<*const T>,
}

#[derive(Debug)]
struct Node<T> {
    value: T,
    head: Key<Node<T>>,
    tail: Key<Node<T>>,
}

fn main() {

}