error[E0716]: temporary value dropped while borrowed
  --> tests/ui/no_uaf_2.rs:30:21
   |
29 |     s.as_ref().operate_in(|r| {
   |                            - has type `OperateIn<'1, MyStructKey>`
30 |         r.cell.set(&String::from("hello world")); // temporary dropped at end of this statement
   |         ------------^^^^^^^^^^^^^^^^^^^^^^^^^^^-- temporary value is freed at the end of this statement
   |         |           |
   |         |           creates a temporary value which is freed while still in use
   |         argument requires that borrow lasts for `'1`