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use core::pin::Pin;
use futures_core::future::{FusedFuture, Future};
use futures_core::task::{Context, Poll};
use pin_project::pin_project;
#[pin_project(project = MaybeDoneProj, project_replace = MaybeDoneProjOwn)]
#[derive(Debug)]
pub enum MaybeDone<Fut: Future> {
Future(#[pin] Fut),
Done(Fut::Output),
Gone,
}
pub fn maybe_done<Fut: Future>(future: Fut) -> MaybeDone<Fut> {
MaybeDone::Future(future)
}
impl<Fut: Future> MaybeDone<Fut> {
#[inline]
pub fn output_mut(self: Pin<&mut Self>) -> Option<&mut Fut::Output> {
match self.project() {
MaybeDoneProj::Done(res) => Some(res),
_ => None,
}
}
#[inline]
pub fn take_output(self: Pin<&mut Self>) -> Option<Fut::Output> {
match &*self {
MaybeDone::Done(_) => {}
MaybeDone::Future(_) | MaybeDone::Gone => return None,
}
match self.project_replace(MaybeDone::Gone) {
MaybeDoneProjOwn::Done(output) => Some(output),
_ => unreachable!(),
}
}
}
impl<Fut: Future> FusedFuture for MaybeDone<Fut> {
fn is_terminated(&self) -> bool {
match self {
MaybeDone::Future(_) => false,
MaybeDone::Done(_) | MaybeDone::Gone => true,
}
}
}
impl<Fut: Future> Future for MaybeDone<Fut> {
type Output = ();
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
match self.as_mut().project() {
MaybeDoneProj::Future(f) => {
let res = ready!(f.poll(cx));
self.set(MaybeDone::Done(res));
}
MaybeDoneProj::Done(_) => {}
MaybeDoneProj::Gone => panic!("MaybeDone polled after value taken"),
}
Poll::Ready(())
}
}