error[E0597]: `*a` does not live long enough
  --> $DIR/destructor-restrictions.rs:19:5
   |
18 |         *a.borrow() + 1    //~ ERROR `*a` does not live long enough
   |          - borrow occurs here
19 |     };
   |     ^- borrowed value needs to live until here
   |     |
   |     `*a` dropped here while still borrowed

error: aborting due to previous error(s)