    /// }
    /// ```
    fn into_cache<A>(self, upstream: &Addr<A>) -> QueryCache<A, Self>
    where
        A: Actor,
        Self: Message + Send + Sized,
        Self::Result: MessageResponse<A, Self> + Send + 'static,
    {
        QueryCache {
            upstream: upstream.clone(),
            message: self,
        }