A borrowed variable was used by a closure.
Erroneous code example:
fn you_know_nothing(jon_snow: &mut i32) { let nights_watch = &jon_snow; let starks = || { *jon_snow = 3; // error: closure requires unique access to `jon_snow` // but it is already borrowed }; println!("{}", nights_watch); }
In here, jon_snow
is already borrowed by the nights_watch
reference, so it cannot be borrowed by the starks
closure at the same time. To fix this issue, you can create the closure after the borrow has ended:
fn you_know_nothing(jon_snow: &mut i32) { let nights_watch = &jon_snow; println!("{}", nights_watch); let starks = || { *jon_snow = 3; }; }
Or, if the type implements the Clone
trait, you can clone it between closures:
fn you_know_nothing(jon_snow: &mut i32) { let mut jon_copy = jon_snow.clone(); let starks = || { *jon_snow = 3; }; println!("{}", jon_copy); }