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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();
}
}))
}
}