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use futures_core::future::{FusedFuture, Future};
use futures_core::task::{Context, Poll};
use pin_project::pin_project;
use std::pin::Pin;
#[pin_project]
#[derive(Debug, Clone)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct PendingOnce<Fut> {
#[pin]
future: Fut,
polled_before: bool,
}
impl<Fut: Future> PendingOnce<Fut> {
pub(super) fn new(future: Fut) -> Self {
Self { future, polled_before: false }
}
}
impl<Fut: Future> Future for PendingOnce<Fut> {
type Output = Fut::Output;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let this = self.project();
if *this.polled_before {
this.future.poll(cx)
} else {
*this.polled_before = true;
cx.waker().wake_by_ref();
Poll::Pending
}
}
}
impl<Fut: FusedFuture> FusedFuture for PendingOnce<Fut> {
fn is_terminated(&self) -> bool {
self.polled_before && self.future.is_terminated()
}
}