error[E0605]: non-primitive cast: `Foo` as `isize`
  --> $DIR/nonscalar-cast.rs:15:20
   |
LL |     println!("{}", Foo { x: 1 } as isize);
   |                    ^^^^^^^^^^^^^^^^^^^^^ help: consider using the `From` trait instead: `isize::from(Foo { x: 1 })`
   |
   = note: an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object

error: aborting due to previous error

For more information about this error, try `rustc --explain E0605`.