error: casting immutable reference to a mutable reference
  --> $DIR/cast_ref_to_mut.rs:18:9
   |
LL |         (*(a as *const _ as *mut String)).push_str(" world");
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `-D clippy::cast-ref-to-mut` implied by `-D warnings`
   = note: consider implementing `UnsafeCell` instead

error: casting immutable reference to a mutable reference
  --> $DIR/cast_ref_to_mut.rs:19:9
   |
LL |         *(a as *const _ as *mut _) = String::from("Replaced");
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: consider implementing `UnsafeCell` instead

error: casting immutable reference to a mutable reference
  --> $DIR/cast_ref_to_mut.rs:20:9
   |
LL |         *(a as *const _ as *mut String) += " world";
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: consider implementing `UnsafeCell` instead

error: aborting due to 3 previous errors