pub fn last_edge(self) -> Handle<Self, marker::Edge> {
        let len = self.len();
        unsafe { Handle::new_edge(self, len) }
    }
Temporarily takes out another, mutable reference to the same node. Beware, as
this method is very dangerous, doubly so since it may not immediately appear
dangerous.

Because mutable pointers can roam anywhere around the tree, the returned
pointer can easily be used to make t
benchmarks/haystacks/code/rust-library.rs