error[E0308]: `?` operator has incompatible types
  --> $DIR/issue-100246.rs:28:24
   |
LL |     let other: Other = downcast()?;
   |                        ^^^^^^^^^^^ expected struct `Other`, found reference
   |
   = note: `?` operator cannot convert from `&_` to `Other`
   = note: expected struct `Other`
           found reference `&_`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.