blob: 7c22f2c316006e4153a4f50160c2ecd28f7461cd [file] [log] [blame]
use core::default::Default;
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::future::Future;
use futures_core::stream::TryStream;
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A stream combinator which attempts to concatenate the results of a stream into the
/// first yielded item.
///
/// This structure is produced by the `TryStream::try_concat` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct TryConcat<St: TryStream> {
stream: St,
accum: Option<St::Ok>,
}
impl<St: TryStream + Unpin> Unpin for TryConcat<St> {}
impl<St> TryConcat<St>
where
St: TryStream,
St::Ok: Extend<<St::Ok as IntoIterator>::Item> + IntoIterator + Default,
{
unsafe_pinned!(stream: St);
unsafe_unpinned!(accum: Option<St::Ok>);
pub(super) fn new(stream: St) -> TryConcat<St> {
TryConcat {
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(mut self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Self::Output> {
loop {
match ready!(self.as_mut().stream().try_poll_next(lw)) {
Some(Ok(x)) => {
let accum = self.as_mut().accum();
if let Some(a) = accum {
a.extend(x)
} else {
*accum = Some(x)
}
},
Some(Err(e)) => return Poll::Ready(Err(e)),
None => {
return Poll::Ready(Ok(self.as_mut().accum().take().unwrap_or_default()))
}
}
}
}
}