Collaterally moved error when deconstructing a Box of pairs

Question

The following two lines:

let x = Box::new((\"slefj\".to_string(), \"a\".to_string()));
let (a, b) = *x;

produce the error:

Answer 1

You have stumbled on a limitation on destructuring and boxes. Luckily, it's easy to work around these. All you need to do is introduce a new intermediary variable that contains the whole structure, and destructure from that:

let x = Box::new(("slefj".to_string(), "a".to_string()));
let pair = *x;
let (a, b) = pair;

The second example:

let pair = *x;
match pair {
    Tree::Pair(a, b) => Tree::Pair(a, b),
    _ => Tree::Nil,
};

Answer 2

The good news is that your original code works as-is now that non-lexical lifetimes are enabled by default:

fn main() {
    let x = Box::new(("slefj".to_string(), "a".to_string()));
    let (a, b) = *x;
}

The borrow checker's capability to track the moves out of the box is enhanced, allowing the code to compile.