trait Base {
    type Item;
    type Item2;
}

trait Service {
    type R;
    type E;
    type C: Base<Item = Self::R, Item2 = Self::E>;
}

fn create() -> impl Service {
    struct BaseImpl {}
    impl Base for BaseImpl {
        type Item = u64;
        type Item2 = String;
    }

    struct ServiceImpl {}
    impl Service for ServiceImpl {
        type R = u64;
        type E = String;
        type C = BaseImpl;
    }

    ServiceImpl {}
}

struct S1<T: Service> {
    service: T,
}

struct S2<T: Service> {
    s1: S1<T>,
}

fn main() {
    let s1 = S1 { service: create() };
}