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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);
}