1 error[E0596]: cannot borrow data in a `&` reference as mutable
2 --> $DIR/index-mut-help-with-impl.rs:9:5
4 LL | Index::index(&v, 1..2).make_ascii_uppercase();
5 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
7 error: aborting due to previous error
9 For more information about this error, try `rustc --explain E0596`.