error[E0308]: mismatched types
  --> $DIR/arg-type-mismatch.rs:5:30
   |
LL | fn main() { let i: (); i = f(()); }
   |                              ^^ expected isize, found ()
   |
   = note: expected type `isize`
              found type `()`

error: aborting due to previous error

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