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    use sink::Sink;

    use {Poll, StartSend, Stream};

    /// Sink for the `Sink::sink_map_err` combinator.
    #[derive(Debug)]
    #[must_use = "sinks do nothing unless polled"]
    pub struct SinkMapErr<S, F> {
        sink: S,
        f: Option<F>,
    }

    pub fn new<S, F>(s: S, f: F) -> SinkMapErr<S, F> {
        SinkMapErr { sink: s, f: Some(f) }
    }

    impl<S, E> SinkMapErr<S, E> {
        /// Get a shared reference to the inner sink.
        pub fn get_ref(&self) -> &S {
            &self.sink
        }

        /// Get a mutable reference to the inner sink.
        pub fn get_mut(&mut self) -> &mut S {
            &mut self.sink
        }

        /// Consumes this combinator, returning the underlying sink.
        ///
        /// Note that this may discard intermediate state of this combinator, so
        /// care should be taken to avoid losing resources when this is called.
        pub fn into_inner(self) -> S {
            self.sink
        }
    }

    impl<S, F, E> Sink for SinkMapErr<S, F>
        where S: Sink,
              F: FnOnce(S::SinkError) -> E,
    {
        type SinkItem = S::SinkItem;
        type SinkError = E;

        fn start_send(&mut self, item: Self::SinkItem) -> StartSend<Self::SinkItem, Self::SinkError> {
            self.sink.start_send(item).map_err(|e| self.f.take().expect("cannot use MapErr after an error")(e))
        }

        fn poll_complete(&mut self) -> Poll<(), Self::SinkError> {
            self.sink.poll_complete().map_err(|e| self.f.take().expect("cannot use MapErr after an error")(e))
        }

        fn close(&mut self) -> Poll<(), Self::SinkError> {
            self.sink.close().map_err(|e| self.f.take().expect("cannot use MapErr after an error")(e))
        }
    }

    impl<S: Stream, F> Stream for SinkMapErr<S, F> {
        type Item = S::Item;
        type Error = S::Error;

        fn poll(&mut self) -> Poll<Option<S::Item>, S::Error> {
            self.sink.poll()
        }
    }

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