tree.rs

struct Tree {
    root: *mut Node,
}

impl Tree {
    fn new() -> Tree {
        Tree { root: ptr::null_mut() }
    }

    pub fn insert(&mut self, value: i32) {
        let mut root = self.root;
        self.insert_node(&mut root, value);
    }

    fn insert_node(&mut self, n: &mut *mut Node, value: i32) {
        assert!(*n == self.root); // both are 0x0
        if n.is_null() {
            unsafe {
                let mut node: *mut Node = mem::transmute(Box::new(Node {
                    left: ptr::null_mut(),
                    right: ptr::null_mut(),
                    value: value,
                }));
                mem::replace(n, node);
                assert!(*n == node);
                assert!(self.root == (*n)); // fails, self.root still points to 0x0
            }
        }
    }
}

struct Node {
    left: *mut Node,
    right: *mut Node,
    value: i32,
}