Fun with the usage crate

phantom_ids.rs

use usage::Usage;

struct Author;
struct CanonicalAuthor;
struct Title;

type AuthorId = Usage<Author, i32>;
type CanonicalAuthorId = Usage<CanonicalAuthor, i32>;
type TitleId = Usage<Title, i32>;

fn main() {
    let tolkien_id = AuthorId::from(1);
    let heinlein_id = AuthorId::from(2);
    let dune_id = TitleId::from(1);

    // Can't add without dereferencing:
    let bingo = *tolkien_id + *heinlein_id;
    println!("{bingo:?}");
    
    // Comparable as is:
    if tolkien_id == heinlein_id {
        println!("What, they are the same!?");
    } else {
        println!("Not the same author.");
    }
    // Does not compile:
    /*
    if tolkien_id == dune_id {
        println!("What, same!?");
    } else {
        println!("What, comparable!?");
    }
    */
}