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    use core::pin::Pin;
    use futures_core::future::{Future, FusedFuture};
    use futures_core::ready;
    use futures_core::task::{Context, Poll};
    use pin_project_lite::pin_project;

    pin_project! {
        /// Future for the [`fuse`](super::FutureExt::fuse) method.
        #[derive(Debug)]
        #[must_use = "futures do nothing unless you `.await` or poll them"]
        pub struct Fuse<Fut> {
            #[pin]
            inner: Option<Fut>,
        }
    }

    impl<Fut> Fuse<Fut> {
        pub(super) fn new(f: Fut) -> Self {
            Self { inner: Some(f) }
        }
    }

    impl<Fut: Future> Fuse<Fut> {
        /// Creates a new `Fuse`-wrapped future which is already terminated.
        ///
        /// This can be useful in combination with looping and the `select!`
        /// macro, which bypasses terminated futures.
        ///
        /// # Examples
        ///
        /// ```
        /// # futures::executor::block_on(async {
        /// use futures::channel::mpsc;
        /// use futures::future::{Fuse, FusedFuture, FutureExt};
        /// use futures::select;
        /// use futures::stream::StreamExt;
        /// use futures::pin_mut;
        ///
        /// let (sender, mut stream) = mpsc::unbounded();
        ///
        /// // Send a few messages into the stream
        /// sender.unbounded_send(()).unwrap();
        /// sender.unbounded_send(()).unwrap();
        /// drop(sender);
        ///
        /// // Use `Fuse::terminated()` to create an already-terminated future
        /// // which may be instantiated later.
        /// let foo_printer = Fuse::terminated();
        /// pin_mut!(foo_printer);
        ///
        /// loop {
        ///     select! {
        ///         _ = foo_printer => {},
        ///         () = stream.select_next_some() => {
        ///             if !foo_printer.is_terminated() {
        ///                 println!("Foo is already being printed!");
        ///             } else {
        ///                 foo_printer.set(async {
        ///                     // do some other async operations
        ///                     println!("Printing foo from `foo_printer` future");
        ///                 }.fuse());
        ///             }
        ///         },
        ///         complete => break, // `foo_printer` is terminated and the stream is done
        ///     }
        /// }
        /// # });
        /// ```
        pub fn terminated() -> Self {
            Self { inner: None }
        }
    }

    impl<Fut: Future> FusedFuture for Fuse<Fut> {
        fn is_terminated(&self) -> bool {
            self.inner.is_none()
        }
    }

    impl<Fut: Future> Future for Fuse<Fut> {
        type Output = Fut::Output;

        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Fut::Output> {
            Poll::Ready(match self.as_mut().project().inner.as_pin_mut() {
                Some(fut) => {
                    let output = ready!(fut.poll(cx));
                    self.project().inner.set(None);
                    output
                },
                None => return Poll::Pending,
            })
        }
    }