Function race_stream 

pub fn race_stream<'a, SVC, SVCS, F, Fut, S, T, E>(
    services: SVCS,
    f: F,
) -> impl Stream<Item = Result<T, Error<E>>> + 'a
where
    F: FnMut(SVC) -> Fut + Copy + 'a,
    Fut: Future<Output = Option<S>> + 'a,
    SVCS: IntoIterator<Item = SVC> + 'a,
    SVC: 'a,
    S: Stream<Item = Result<T, E>>,
    E: Send + 'a,
    T: Send + 'a,

Runs an operation returning a stream on all services.

The passed async function describes the operation to run on each service.

The returned Option<_> controls whether to ignore a response, such as an error, or an empty stream (and continue with other backends) or return it.