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