#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#[derive(PartialEq)]
enum BookFormat {
    Paperback,
    Hardback,
    Ebook,
}
struct Book {
    isbn: i32,
    format: BookFormat,
}
impl PartialEq<BookFormat> for Book {
    fn eq(&self, other: &BookFormat) -> bool {
        self.format == *other
    }
}
impl PartialEq<Book> for BookFormat {
    fn eq(&self, other: &Book) -> bool {
        *self == other.format
    }
}
fn main() {
    let b1 = Book {
        isbn: 3,
        format: BookFormat::Paperback,
    };
    assert!(b1 == BookFormat::Paperback);
    assert!(BookFormat::Ebook != b1);
}