error[E0605]: non-primitive cast: `u32` as `()` --> $DIR/cast-to-nil.rs:2:21 | LL | fn main() { let u = 0u32 as (); } | ^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0605`.