error[E0384]: cannot assign twice to immutable variable `b` --> $DIR/issue-45199.rs:6:5 | LL | let b: Box; | - help: make this binding mutable: `mut b` ... LL | b = Box::new(1); | - first assignment to `b` LL | b = Box::new(2); | ^ cannot assign twice to immutable variable error[E0384]: cannot assign twice to immutable variable `b` --> $DIR/issue-45199.rs:14:5 | LL | let b = Box::new(1); | - | | | first assignment to `b` | help: make this binding mutable: `mut b` ... LL | b = Box::new(2); | ^ cannot assign twice to immutable variable error[E0384]: cannot assign to immutable argument `b` --> $DIR/issue-45199.rs:20:5 | LL | fn test_args(b: Box) { | - help: make this binding mutable: `mut b` LL | LL | b = Box::new(2); | ^ cannot assign to immutable argument error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0384`.