error[E0594]: cannot assign to `*y`, as `y` is not declared as mutable --> $DIR/immut-function-arguments.rs:5:5 | LL | fn f(y: Box) { | - help: consider changing this to be mutable: `mut y` LL | *y = 5; //[ast]~ ERROR cannot assign | ^^^^^^ cannot assign error[E0594]: cannot assign to `*q`, as `q` is not declared as mutable --> $DIR/immut-function-arguments.rs:10:35 | LL | let _frob = |q: Box| { *q = 2; }; //[ast]~ ERROR cannot assign | - ^^^^^^ cannot assign | | | help: consider changing this to be mutable: `mut q` error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0594`.