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use std::{future::IntoFuture, time::Duration};
use futures::{stream, Stream};
use tokio::time::timeout;
async fn immediately<F>(fut: F) -> F::Output
where
F: IntoFuture,
{
// I haven't been particularly rigorous here. Zero delay _seems to work_,
// but this can be set higher; it makes tests that fail to meet the
// "immediate" expectation take longer, but gives slow tests time to
// succeed, as well.
let duration = Duration::from_nanos(0);
timeout(duration, fut)
.await
.expect("expected result immediately")
}
// This is only intended for streams, since their `next()`, `collect()`, and
// so on can all block indefinitely on an empty stream. There's no need to
// force immediacy on futures that "can't" block forever, and it can hide logic
// errors if you do that.
//
// The impls below _could_ be replaced with a blanket impl for all future
// types, otherwise. The choice to restrict impls to stream futures is
// deliberate.
pub trait Immediately {
type Output;
async fn immediately(self) -> Self::Output;
}
impl<'a, St> Immediately for stream::Next<'a, St>
where
St: Stream + Unpin + ?Sized,
{
type Output = Option<<St as Stream>::Item>;
async fn immediately(self) -> Self::Output {
immediately(self).await
}
}
impl<St, C> Immediately for stream::Collect<St, C>
where
St: Stream,
C: Default + Extend<<St as Stream>::Item>,
{
type Output = C;
async fn immediately(self) -> Self::Output {
immediately(self).await
}
}
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