| //! Definition of the TryMaybeDone combinator |
| |
| use super::assert_future; |
| use core::mem; |
| use core::pin::Pin; |
| use futures_core::future::{FusedFuture, Future, TryFuture}; |
| use futures_core::ready; |
| use futures_core::task::{Context, Poll}; |
| |
| /// A future that may have completed with an error. |
| /// |
| /// This is created by the [`try_maybe_done()`] function. |
| #[derive(Debug)] |
| pub enum TryMaybeDone<Fut: TryFuture> { |
| /// A not-yet-completed future |
| Future(/* #[pin] */ Fut), |
| /// The output of the completed future |
| Done(Fut::Ok), |
| /// The empty variant after the result of a [`TryMaybeDone`] has been |
| /// taken using the [`take_output`](TryMaybeDone::take_output) method, |
| /// or if the future returned an error. |
| Gone, |
| } |
| |
| impl<Fut: TryFuture + Unpin> Unpin for TryMaybeDone<Fut> {} |
| |
| /// Wraps a future into a `TryMaybeDone` |
| pub fn try_maybe_done<Fut: TryFuture>(future: Fut) -> TryMaybeDone<Fut> { |
| assert_future::<Result<(), Fut::Error>, _>(TryMaybeDone::Future(future)) |
| } |
| |
| impl<Fut: TryFuture> TryMaybeDone<Fut> { |
| /// Returns an [`Option`] containing a mutable reference to the output of the future. |
| /// The output of this method will be [`Some`] if and only if the inner |
| /// future has completed successfully and [`take_output`](TryMaybeDone::take_output) |
| /// has not yet been called. |
| #[inline] |
| pub fn output_mut(self: Pin<&mut Self>) -> Option<&mut Fut::Ok> { |
| unsafe { |
| match self.get_unchecked_mut() { |
| TryMaybeDone::Done(res) => Some(res), |
| _ => None, |
| } |
| } |
| } |
| |
| /// Attempt to take the output of a `TryMaybeDone` without driving it |
| /// towards completion. |
| #[inline] |
| pub fn take_output(self: Pin<&mut Self>) -> Option<Fut::Ok> { |
| match &*self { |
| Self::Done(_) => {} |
| Self::Future(_) | Self::Gone => return None, |
| } |
| unsafe { |
| match mem::replace(self.get_unchecked_mut(), Self::Gone) { |
| TryMaybeDone::Done(output) => Some(output), |
| _ => unreachable!(), |
| } |
| } |
| } |
| } |
| |
| impl<Fut: TryFuture> FusedFuture for TryMaybeDone<Fut> { |
| fn is_terminated(&self) -> bool { |
| match self { |
| Self::Future(_) => false, |
| Self::Done(_) | Self::Gone => true, |
| } |
| } |
| } |
| |
| impl<Fut: TryFuture> Future for TryMaybeDone<Fut> { |
| type Output = Result<(), Fut::Error>; |
| |
| fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { |
| unsafe { |
| match self.as_mut().get_unchecked_mut() { |
| TryMaybeDone::Future(f) => match ready!(Pin::new_unchecked(f).try_poll(cx)) { |
| Ok(res) => self.set(Self::Done(res)), |
| Err(e) => { |
| self.set(Self::Gone); |
| return Poll::Ready(Err(e)); |
| } |
| }, |
| TryMaybeDone::Done(_) => {} |
| TryMaybeDone::Gone => panic!("TryMaybeDone polled after value taken"), |
| } |
| } |
| Poll::Ready(Ok(())) |
| } |
| } |