Error code E0524
A variable which requires unique access is being used in more than one closure at the same time.
Erroneous code example:
#![allow(unused)] fn main() { fn set(x: &mut isize) { *x = 4; } fn dragoooon(x: &mut isize) { let mut c1 = || set(x); let mut c2 = || set(x); // error! c2(); c1(); } }
To solve this issue, multiple solutions are available. First, is it required
for this variable to be used in more than one closure at a time? If it is the
case, use reference counted types such as Rc
(or Arc
if it runs
concurrently):
#![allow(unused)] fn main() { use std::rc::Rc; use std::cell::RefCell; fn set(x: &mut isize) { *x = 4; } fn dragoooon(x: &mut isize) { let x = Rc::new(RefCell::new(x)); let y = Rc::clone(&x); let mut c1 = || { let mut x2 = x.borrow_mut(); set(&mut x2); }; let mut c2 = || { let mut x2 = y.borrow_mut(); set(&mut x2); }; // ok! c2(); c1(); } }
If not, just run closures one at a time:
#![allow(unused)] fn main() { fn set(x: &mut isize) { *x = 4; } fn dragoooon(x: &mut isize) { { // This block isn't necessary since non-lexical lifetimes, it's just to // make it more clear. let mut c1 = || set(&mut *x); c1(); } // `c1` has been dropped here so we're free to use `x` again! let mut c2 = || set(&mut *x); c2(); } }