trait SessionKind {
    type CreatorRelatedType;
}

trait ServerSessionKind: SessionKind {
    type CreatorRelatedType: AbstractCreatorType;
}

trait AbstractCreatorType {}

trait FinalizedSessionKind: SessionKind {
    type CreatorRelatedType: ConcreteCreatorType;
}

trait ConcreteCreatorType {}

trait SessionV1Kind: SessionKind {}

trait ServerSessionV1Kind: SessionV1Kind + ServerSessionKind {}

trait SessionV2Kind: SessionKind {}

trait ServerSessionV2Kind: SessionV2Kind + ServerSessionKind {}

enum Session<T: SessionKind> {
    V1(SessionV1<T>),
    V2(SessionV2<T>)
}

struct SessionV2<T: SessionV2Kind> {
    _pd: std::marker::PhantomData<T>,
}

struct SessionV1<T: SessionV1Kind> {
    some_field_depending_on_session_kind: SomeV1FieldType<T>,
}

struct SomeV1FieldType<T: SessionV1Kind> {
    some_unrelated_field: u64,
    some_session_kind_related_field: T::CreatorRelatedType,
}