A variable which requires unique access is being used in more than one closure at the same time.
Erroneous code example:
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):
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:
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();
}