error[E0502]: cannot borrow `slice_1` as mutable because it is also borrowed as immutable
 --> compile_fail_tests/mut_lock_7.rs
  |
  |         let slice_2 = slice_1.slice(..).unwrap();
  |                       ----------------- immutable borrow occurs here
...
  |     let _ = slice_1.get_mut(0).unwrap();
  |             ^^^^^^^^^^^^^^^^^^ mutable borrow occurs here
  |
  |     let _ = slice_3.get(1).unwrap();
  |             -------------- immutable borrow later used here