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

    pin_project! {
        /// Stream for the [`try_flatten`](super::TryStreamExt::try_flatten) method.
        #[derive(Debug)]
        #[must_use = "streams do nothing unless polled"]
        pub struct TryFlatten<St>
        where
            St: TryStream,
        {
            #[pin]
            stream: St,
            #[pin]
            next: Option<St::Ok>,
        }
    }

    impl<St> TryFlatten<St>
    where
        St: TryStream,
        St::Ok: TryStream,
        <St::Ok as TryStream>::Error: From<St::Error>,
    {
        pub(super) fn new(stream: St) -> Self {
            Self { stream, next: None }
        }

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

    impl<St> FusedStream for TryFlatten<St>
    where
        St: TryStream + FusedStream,
        St::Ok: TryStream,
        <St::Ok as TryStream>::Error: From<St::Error>,
    {
        fn is_terminated(&self) -> bool {
            self.next.is_none() && self.stream.is_terminated()
        }
    }

    impl<St> Stream for TryFlatten<St>
    where
        St: TryStream,
        St::Ok: TryStream,
        <St::Ok as TryStream>::Error: From<St::Error>,
    {
        type Item = Result<<St::Ok as TryStream>::Ok, <St::Ok as TryStream>::Error>;

        fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
            let mut this = self.project();

            Poll::Ready(loop {
                if let Some(s) = this.next.as_mut().as_pin_mut() {
                    if let Some(item) = ready!(s.try_poll_next(cx)?) {
                        break Some(Ok(item));
                    } else {
                        this.next.set(None);
                    }
                } else if let Some(s) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
                    this.next.set(Some(s));
                } else {
                    break None;
                }
            })
        }
    }

    // Forwarding impl of Sink from the underlying stream
    #[cfg(feature = "sink")]
    impl<S, Item> Sink<Item> for TryFlatten<S>
    where
        S: TryStream + Sink<Item>,
    {
        type Error = <S as Sink<Item>>::Error;

        delegate_sink!(stream, Item);
    }