blob: 2317ad05dccb7b218ac21b18042ede5f25dcfde5 [file] [log] [blame]
use core::fmt::{Debug, Formatter, Result as FmtResult};
use core::marker::Unpin;
use core::pin::Pin;
use core::default::Default;
use futures_core::future::Future;
use futures_core::stream::Stream;
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A stream combinator to concatenate the results of a stream into the first
/// yielded item.
///
/// This structure is produced by the `Stream::concat` method.
#[must_use = "streams do nothing unless polled"]
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> Debug for Concat<St>
where St: Stream + Debug,
St::Item: Debug,
{
fn fmt(&self, fmt: &mut Formatter) -> FmtResult {
fmt.debug_struct("Concat")
.field("accum", &self.accum)
.finish()
}
}
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>, lw: &LocalWaker
) -> Poll<Self::Output> {
loop {
match self.as_mut().stream().poll_next(lw) {
Poll::Pending => return Poll::Pending,
Poll::Ready(None) => {
return Poll::Ready(self.as_mut().accum().take().unwrap_or_default())
}
Poll::Ready(Some(e)) => {
let accum = self.as_mut().accum();
if let Some(a) = accum {
a.extend(e)
} else {
*accum = Some(e)
}
}
}
}
}
}