union CellValue {
    tag: TaggedPtr<Aligned, 2>,
    num: Decimal,
    str: ManuallyDrop<ThinVec<u8>>,
    formula: ManuallyDrop<Rc<Formula>>,
    iter: ManuallyDrop<Box<dyn Iterator<Item = CellValue>>>,
}

struct UsersService {
    config: &'static Config,
}

struct OrdersService {
    config: &'static Config,
}

// ...

fn load() -> Result<&'static Config, Error> {
    // ...
    return Ok(Box::leak(Box::new(config)));
}

// ...

let config = config::load()?;

let users_service = UsersService::new(config);

let orders_service = OrdersService::new(config);

User space scheduling

struct Id<T> {
    inner: u64,
    _marker: std::marker::PhantomData<T>,
}
impl<T> Id<T> {
    pub fn new(inner: u64) -> Self { 
       Self {
           inner, 
           _marker: std::marker::PhantomData
        }
    }
}
struct UserIdMarker;
struct GroupIdMarker;

pub type UserId = Id<UserIdMarker>;
pub type GroupId = Id<GroupIdMarker>;
//...

fn ping_user(id: UserId) {
    //...
}
ping_user(GroupId::new(12345)); // This triggers an error

$ aptitude search librust- | grep -vE "^v " | wc -l
2336