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    use crate::stream::StreamExt;
    use core::pin::Pin;
    use futures_core::future::{FusedFuture, Future};
    use futures_core::ready;
    use futures_core::stream::Stream;
    use futures_core::task::{Context, Poll};

    /// Future for the [`into_future`](super::StreamExt::into_future) method.
    #[derive(Debug)]
    #[must_use = "futures do nothing unless you `.await` or poll them"]
    pub struct StreamFuture<St> {
        stream: Option<St>,
    }

    impl<St: Stream + Unpin> StreamFuture<St> {
        pub(super) fn new(stream: St) -> Self {
            Self { stream: Some(stream) }
        }

        /// Acquires a reference to the underlying stream that this combinator is
        /// pulling from.
        ///
        /// This method returns an `Option` to account for the fact that `StreamFuture`'s
        /// implementation of `Future::poll` consumes the underlying stream during polling
        /// in order to return it to the caller of `Future::poll` if the stream yielded
        /// an element.
        pub fn get_ref(&self) -> Option<&St> {
            self.stream.as_ref()
        }

        /// Acquires a mutable reference to the underlying stream that this
        /// combinator is pulling from.
        ///
        /// Note that care must be taken to avoid tampering with the state of the
        /// stream which may otherwise confuse this combinator.
        ///
        /// This method returns an `Option` to account for the fact that `StreamFuture`'s
        /// implementation of `Future::poll` consumes the underlying stream during polling
        /// in order to return it to the caller of `Future::poll` if the stream yielded
        /// an element.
        pub fn get_mut(&mut self) -> Option<&mut St> {
            self.stream.as_mut()
        }

        /// Acquires a pinned mutable reference to the underlying stream that this
        /// combinator is pulling from.
        ///
        /// Note that care must be taken to avoid tampering with the state of the
        /// stream which may otherwise confuse this combinator.
        ///
        /// This method returns an `Option` to account for the fact that `StreamFuture`'s
        /// implementation of `Future::poll` consumes the underlying stream during polling
        /// in order to return it to the caller of `Future::poll` if the stream yielded
        /// an element.
        pub fn get_pin_mut(self: Pin<&mut Self>) -> Option<Pin<&mut St>> {
            self.get_mut().stream.as_mut().map(Pin::new)
        }

        /// Consumes this combinator, returning the underlying stream.
        ///
        /// Note that this may discard intermediate state of this combinator, so
        /// care should be taken to avoid losing resources when this is called.
        ///
        /// This method returns an `Option` to account for the fact that `StreamFuture`'s
        /// implementation of `Future::poll` consumes the underlying stream during polling
        /// in order to return it to the caller of `Future::poll` if the stream yielded
        /// an element.
        pub fn into_inner(self) -> Option<St> {
            self.stream
        }
    }

    impl<St: Stream + Unpin> FusedFuture for StreamFuture<St> {
        fn is_terminated(&self) -> bool {
            self.stream.is_none()
        }
    }

    impl<St: Stream + Unpin> Future for StreamFuture<St> {
        type Output = (Option<St::Item>, St);

        fn poll(
            mut self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Self::Output> {
            let item = {
                let s = self.stream.as_mut().expect("polling StreamFuture twice");
                ready!(s.poll_next_unpin(cx))
            };
            let stream = self.stream.take().unwrap();
            Poll::Ready((item, stream))
        }
    }