error[E0499]: cannot borrow `*s` as mutable more than once at a time
  --> $DIR/issue-18566.rs:23:19
   |
LL |     MyPtr(s).poke(s);
   |           -  ---- ^ second mutable borrow occurs here
   |           |  |
   |           |  first borrow later used by call
   |           first mutable borrow occurs here

error: aborting due to previous error

For more information about this error, try `rustc --explain E0499`.