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

error: aborting due to 1 previous error

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