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use core::pin::Pin;
use futures_core::future::{Future, FusedFuture};
use futures_core::stream::{Stream, FusedStream};
use futures_core::task::{Context, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct Concat<St: Stream> {
stream: St,
accum: Option<St::Item>,
}
impl<St: Stream + Unpin> Unpin for Concat<St> {}
impl<St> Concat<St>
where St: Stream,
St::Item: Extend<<St::Item as IntoIterator>::Item> +
IntoIterator + Default,
{
unsafe_pinned!(stream: St);
unsafe_unpinned!(accum: Option<St::Item>);
pub(super) fn new(stream: St) -> Concat<St> {
Concat {
stream,
accum: None,
}
}
}
impl<St> Future for Concat<St>
where St: Stream,
St::Item: Extend<<St::Item as IntoIterator>::Item> +
IntoIterator + Default,
{
type Output = St::Item;
fn poll(
mut self: Pin<&mut Self>, cx: &mut Context<'_>
) -> Poll<Self::Output> {
loop {
match ready!(self.as_mut().stream().poll_next(cx)) {
None => {
return Poll::Ready(self.as_mut().accum().take().unwrap_or_default())
}
Some(e) => {
let accum = self.as_mut().accum();
if let Some(a) = accum {
a.extend(e)
} else {
*accum = Some(e)
}
}
}
}
}
}
impl<St> FusedFuture for Concat<St>
where St: FusedStream,
St::Item: Extend<<St::Item as IntoIterator>::Item> +
IntoIterator + Default,
{
fn is_terminated(&self) -> bool {
self.accum.is_none() && self.stream.is_terminated()
}
}