error[E0594]: cannot assign to `fancy_ref.num`, which is behind a `&` reference --> $DIR/E0389.rs:8:5 | LL | fancy_ref.num = 6; | ^^^^^^^^^^^^^^^^^ `fancy_ref` is a `&` reference, so the data it refers to cannot be written | help: consider changing this to be a mutable reference | LL | let fancy_ref = &mut (&mut fancy); | +++ error: aborting due to previous error For more information about this error, try `rustc --explain E0594`.