Code shared from the Rust Playground

playground.rs

type BarberId= usize;
type ShopId = usize;

struct Shop {
    barber: Option<BarberId>,
}

struct Barber {
    shop: Option<ShopId>,
}


struct MyDataStore {
    barbers: Vec<Barber>,
    shops: Vec<Shop>
}

impl MyDataStore {
    fn add_barber(&mut self, barber: Barber) -> BarberId {
        let id = self.barbers.len();
        self.barbers.push(barber);
        id
    }
    fn add_shop(&mut self, shop: Shop) -> ShopId {
        let id = self.shops.len();
        self.shops.push(shop);
        id
    }
    
    fn assign_barber_and_shop(&mut self, shop_id: ShopId, barber_id: BarberId) {
       self.barbers[barber_id].shop = Some(shop_id);
       self.shops[shop_id].barber = Some(barber_id);
    }
}