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    use core::pin::Pin;
    use futures_core::ready;
    use futures_core::stream::FusedStream;
    use futures_core::future::{Future, FusedFuture};
    use futures_core::task::{Context, Poll};
    use crate::stream::StreamExt;

    /// Future for the [`select_next_some`](super::StreamExt::select_next_some)
    /// method.
    #[derive(Debug)]
    #[must_use = "futures do nothing unless you `.await` or poll them"]
    pub struct SelectNextSome<'a, St: ?Sized> {
        stream: &'a mut St,
    }

    impl<'a, St: ?Sized> SelectNextSome<'a, St> {
        pub(super) fn new(stream: &'a mut St) -> Self {
            Self { stream }
        }
    }

    impl<St: ?Sized + FusedStream + Unpin> FusedFuture for SelectNextSome<'_, St> {
        fn is_terminated(&self) -> bool {
            self.stream.is_terminated()
        }
    }

    impl<St: ?Sized + FusedStream + Unpin> Future for SelectNextSome<'_, St> {
        type Output = St::Item;

        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
            assert!(!self.stream.is_terminated(), "SelectNextSome polled after terminated");

            if let Some(item) = ready!(self.stream.poll_next_unpin(cx)) {
                Poll::Ready(item)
            } else {
                debug_assert!(self.stream.is_terminated());
                cx.waker().wake_by_ref();
                Poll::Pending
            }
        }
    }