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    use core::pin::Pin;
    use futures_core::future::Future;
    use futures_core::ready;
    use futures_core::stream::TryStream;
    use futures_core::task::{Context, Poll};
    use pin_project_lite::pin_project;

    pin_project! {
        /// Future for the [`try_concat`](super::TryStreamExt::try_concat) method.
        #[derive(Debug)]
        #[must_use = "futures do nothing unless you `.await` or poll them"]
        pub struct TryConcat<St: TryStream> {
            #[pin]
            stream: St,
            accum: Option<St::Ok>,
        }
    }

    impl<St> TryConcat<St>
    where
        St: TryStream,
        St::Ok: Extend<<St::Ok as IntoIterator>::Item> + IntoIterator + Default,
    {
        pub(super) fn new(stream: St) -> Self {
            Self {
                stream,
                accum: None,
            }
        }
    }

    impl<St> Future for TryConcat<St>
    where
        St: TryStream,
        St::Ok: Extend<<St::Ok as IntoIterator>::Item> + IntoIterator + Default,
    {
        type Output = Result<St::Ok, St::Error>;

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

            Poll::Ready(Ok(loop {
                if let Some(x) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
                    if let Some(a) = this.accum {
                        a.extend(x)
                    } else {
                        *this.accum = Some(x)
                    }
                } else {
                    break this.accum.take().unwrap_or_default();
                }
            }))
        }
    }