Moved value is still accessible

[mdinger]

This looks like a bug to me. No one responded on IRC so I'm uncertain though:

#[derive(Debug)]
struct S {
    val: Option<Box<S>>,
}

fn main() {
    let mut a = S { val: None };
    let _ = S { val: Some(Box::new(a)) };

    // `a` was just moved. I can still assign to it though.
    // kinda seems like a bug.
    a.val = None;

    // assignment works but println fails because of move. kinda weird.
    //println!("{:?}", a.val);
}

playpen

[steveklabnik]

I don't think this is a bug. Moved values aren't usable, but you're not using it, you're assigning a new value to it.

[steveklabnik]

/cc @nikomatsakis

[mdinger]

This can be misleading. A guy was showing this on IRC. If it had triggered a move error he probably would have caught it. As it is, he wasn't noticing that the value had moved. The original question on botbot.

---

The original questions code:

#[derive(Debug)]
pub struct Node<T>{
    pub item: T,
    pub next: Option<Box<Node<T>>>
}

impl <T>Node<T>{
   pub fn new(item: T) -> Node<T> {
       Node::<T> {item: item, next: None}
   }
}

pub fn main() {
    let mut first = Node::new("to");
    let mut second = Node::new("be");
    let mut third = Node::new("or");
    let mut fourth = Node::new("not");
    let fifth = Node::new("to");

    first.next = Some(Box::new(second));
    second.next = Some(Box::new(third));
    third.next = Some(Box::new(fourth));
    fourth.next = Some(Box::new(fifth));

    println!("{:?}", first);
}

[sfackler]

I believe this is a dup of #21232

[steveklabnik]

Ah yes it is