It's not possible to destructure and move from boxes without introducing an additional binding

[renato-zannon]

This program compiles:

struct NonCopy;

fn main() {
    let x = Box::new((NonCopy, NonCopy));

    let pair = *x;
    let (_a, _b) = pair;
}

But this one does not:

struct NonCopy;

fn main() {
    let x = Box::new((NonCopy, NonCopy));
    let (_a, _b) = *x;
}

It fails with:

destr.rs:6:14: 6:16 error: use of moved value: `x`
destr.rs:6     let (_a, _b) = *x;
                        ^~
destr.rs:6:10: 6:12 note: `x` moved here (through moving `x.0`) because it has type `NonCopy`, which is moved by default
destr.rs:6     let (_a, _b) = *x;
                    ^~
destr.rs:6:10: 6:12 help: use `ref` to override
destr.rs:6     let (_a, _b) = *x;
                    ^~
error: aborting due to previous error

[florence]

Another oddity, that seems related:

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

works but:

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

fails with the same "moved value" error.

[goffrie]

I believe this is the same as #16223.

[huonw]

Looks like it; thanks @goffrie (and @renato-zannon and @florence).

@florence I believe that one is because it does it in field order. "" is a &'static strwhich isCopy, so theabinding in the first one doesn't move out ofx, and hence doesn't invalidxfor theb` binding.