error[E0596]: cannot borrow `y.0` as mutable, as it is immutable for the pattern guard --> $DIR/guard-mutability-2.rs:8:37 | LL | Some(ref mut y) if let Some(ref mut z) = *y => { | ^^^^^^^^^ cannot borrow as mutable | = note: variables bound in patterns are immutable until the end of the pattern guard error: aborting due to previous error For more information about this error, try `rustc --explain E0596`.