error[E0277]: expected a `Fn<()>` closure, found `()`
  --> $DIR/issue-22034.rs:8:16
   |
LL |         &mut *(ptr as *mut dyn Fn())
   |                ^^^ expected an `Fn<()>` closure, found `()`
   |
   = help: the trait `Fn<()>` is not implemented for `()`
   = note: wrap the `()` in a closure with no arguments: `|| { /* code */ }`
   = note: required for the cast from `()` to the object type `dyn Fn()`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
