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    use {Poll, Async, Future, AsyncSink};
    use stream::{Stream, Fuse};
    use sink::Sink;

    /// Future for the `Sink::send_all` combinator, which sends a stream of values
    /// to a sink and then waits until the sink has fully flushed those values.
    #[derive(Debug)]
    #[must_use = "futures do nothing unless polled"]
    pub struct SendAll<T, U: Stream> {
        sink: Option<T>,
        stream: Option<Fuse<U>>,
        buffered: Option<U::Item>,
    }

    pub fn new<T, U>(sink: T, stream: U) -> SendAll<T, U>
        where T: Sink,
              U: Stream<Item = T::SinkItem>,
              T::SinkError: From<U::Error>,
    {
        SendAll {
            sink: Some(sink),
            stream: Some(stream.fuse()),
            buffered: None,
        }
    }

    impl<T, U> SendAll<T, U>
        where T: Sink,
              U: Stream<Item = T::SinkItem>,
              T::SinkError: From<U::Error>,
    {
        fn sink_mut(&mut self) -> &mut T {
            self.sink.as_mut().take().expect("Attempted to poll SendAll after completion")
        }

        fn stream_mut(&mut self) -> &mut Fuse<U> {
            self.stream.as_mut().take()
                .expect("Attempted to poll SendAll after completion")
        }

        fn take_result(&mut self) -> (T, U) {
            let sink = self.sink.take()
                .expect("Attempted to poll Forward after completion");
            let fuse = self.stream.take()
                .expect("Attempted to poll Forward after completion");
            (sink, fuse.into_inner())
        }

        fn try_start_send(&mut self, item: U::Item) -> Poll<(), T::SinkError> {
            debug_assert!(self.buffered.is_none());
            if let AsyncSink::NotReady(item) = self.sink_mut().start_send(item)? {
                self.buffered = Some(item);
                return Ok(Async::NotReady)
            }
            Ok(Async::Ready(()))
        }
    }

    impl<T, U> Future for SendAll<T, U>
        where T: Sink,
              U: Stream<Item = T::SinkItem>,
              T::SinkError: From<U::Error>,
    {
        type Item = (T, U);
        type Error = T::SinkError;

        fn poll(&mut self) -> Poll<(T, U), T::SinkError> {
            // If we've got an item buffered already, we need to write it to the
            // sink before we can do anything else
            if let Some(item) = self.buffered.take() {
                try_ready!(self.try_start_send(item))
            }

            loop {
                match self.stream_mut().poll()? {
                    Async::Ready(Some(item)) => try_ready!(self.try_start_send(item)),
                    Async::Ready(None) => {
                        try_ready!(self.sink_mut().close());
                        return Ok(Async::Ready(self.take_result()))
                    }
                    Async::NotReady => {
                        try_ready!(self.sink_mut().poll_complete());
                        return Ok(Async::NotReady)
                    }
                }
            }
        }
    }

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