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    use crate::io::AsyncWrite;

    use std::fmt;
    use std::io;
    use std::pin::Pin;
    use std::task::{Context, Poll};

    cfg_io_util! {
        /// An async writer which will move data into the void.
        ///
        /// This struct is generally created by calling [`sink`][sink]. Please
        /// see the documentation of `sink()` for more details.
        ///
        /// This is an asynchronous version of [`std::io::Sink`][std].
        ///
        /// [sink]: sink()
        /// [std]: std::io::Sink
        pub struct Sink {
            _p: (),
        }

        /// Creates an instance of an async writer which will successfully consume all
        /// data.
        ///
        /// All calls to [`poll_write`] on the returned instance will return
        /// `Poll::Ready(Ok(buf.len()))` and the contents of the buffer will not be
        /// inspected.
        ///
        /// This is an asynchronous version of [`std::io::sink`][std].
        ///
        /// [`poll_write`]: crate::io::AsyncWrite::poll_write()
        /// [std]: std::io::sink
        ///
        /// # Examples
        ///
        /// ```
        /// use tokio::io::{self, AsyncWriteExt};
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     let buffer = vec![1, 2, 3, 5, 8];
        ///     let num_bytes = io::sink().write(&buffer).await?;
        ///     assert_eq!(num_bytes, 5);
        ///     Ok(())
        /// }
        /// ```
        pub fn sink() -> Sink {
            Sink { _p: () }
        }
    }

    impl AsyncWrite for Sink {
        #[inline]
        fn poll_write(
            self: Pin<&mut Self>,
            _: &mut Context<'_>,
            buf: &[u8],
        ) -> Poll<Result<usize, io::Error>> {
            Poll::Ready(Ok(buf.len()))
        }

        #[inline]
        fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
            Poll::Ready(Ok(()))
        }

        #[inline]
        fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
            Poll::Ready(Ok(()))
        }
    }

    impl fmt::Debug for Sink {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.pad("Sink { .. }")
        }
    }

    #[cfg(test)]
    mod tests {
        use super::*;

        #[test]
        fn assert_unpin() {
            crate::is_unpin::<Sink>();
        }
    }