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    use core::fmt;
    use core::pin::Pin;
    use futures_core::ready;
    use futures_core::stream::{FusedStream, Stream};
    use futures_core::task::{Context, Poll};
    #[cfg(feature = "sink")]
    use futures_sink::Sink;
    use pin_project_lite::pin_project;

    use crate::fns::FnMut1;

    pin_project! {
        /// Stream for the [`map`](super::StreamExt::map) method.
        #[must_use = "streams do nothing unless polled"]
        pub struct Map<St, F> {
            #[pin]
            stream: St,
            f: F,
        }
    }

    impl<St, F> fmt::Debug for Map<St, F>
    where
        St: fmt::Debug,
    {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("Map")
                .field("stream", &self.stream)
                .finish()
        }
    }

    impl<St, F> Map<St, F> {
        pub(crate) fn new(stream: St, f: F) -> Self {
            Self { stream, f }
        }

        delegate_access_inner!(stream, St, ());
    }

    impl<St, F> FusedStream for Map<St, F>
        where St: FusedStream,
              F: FnMut1<St::Item>,
    {
        fn is_terminated(&self) -> bool {
            self.stream.is_terminated()
        }
    }

    impl<St, F> Stream for Map<St, F>
        where St: Stream,
              F: FnMut1<St::Item>,
    {
        type Item = F::Output;

        fn poll_next(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Option<Self::Item>> {
            let mut this = self.project();
            let res = ready!(this.stream.as_mut().poll_next(cx));
            Poll::Ready(res.map(|x| this.f.call_mut(x)))
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            self.stream.size_hint()
        }
    }

    // Forwarding impl of Sink from the underlying stream
    #[cfg(feature = "sink")]
    impl<St, F, Item> Sink<Item> for Map<St, F>
        where St: Stream + Sink<Item>,
              F: FnMut1<St::Item>,
    {
        type Error = St::Error;

        delegate_sink!(stream, Item);
    }