1 // run-rustfix
2 
3 // Point at the captured immutable outer variable
4 
foo(mut f: Box<dyn FnMut()>)5 fn foo(mut f: Box<dyn FnMut()>) {
6     f();
7 }
8 
main()9 fn main() {
10     let y = true;
11     foo(Box::new(move || y = !y) as Box<_>);
12     //~^ ERROR cannot assign to `y`, as it is not declared as mutable
13 }
14