blob: 58675cbdc3911593b566e3da58b643d40621370e [file] [log] [blame]
use core::pin::Pin;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{LocalWaker, Poll};
use pin_utils::unsafe_pinned;
/// An adapter for chaining the output of two streams.
///
/// The resulting stream produces items from first stream and then
/// from second stream.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Chain<St1, St2> {
first: Option<St1>,
second: St2,
}
// All interactions with `Pin<&mut Chain<..>>` happen through these methods
impl<St1, St2> Chain<St1, St2>
where St1: Stream,
St2: Stream<Item = St1::Item>,
{
unsafe_pinned!(first: Option<St1>);
unsafe_pinned!(second: St2);
pub(super) fn new(stream1: St1, stream2: St2) -> Chain<St1, St2> {
Chain {
first: Some(stream1),
second: stream2,
}
}
}
impl<St1, St2: FusedStream> FusedStream for Chain<St1, St2> {
fn is_terminated(&self) -> bool {
self.first.is_none() && self.second.is_terminated()
}
}
impl<St1, St2> Stream for Chain<St1, St2>
where St1: Stream,
St2: Stream<Item=St1::Item>,
{
type Item = St1::Item;
fn poll_next(
mut self: Pin<&mut Self>,
lw: &LocalWaker,
) -> Poll<Option<Self::Item>> {
if let Some(first) = self.first().as_pin_mut() {
if let Some(item) = ready!(first.poll_next(lw)) {
return Poll::Ready(Some(item))
}
}
Pin::set(self.first(), None);
self.second().poll_next(lw)
}
}