blob: 0da35f4ab4210d12a350c890b5b403c86f927173 [file] [log] [blame]
use core::pin::PinMut;
use futures_core::stream::Stream;
use futures_core::task::{self, 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 `PinMut<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> Stream for Chain<St1, St2>
where St1: Stream,
St2: Stream<Item=St1::Item>,
{
type Item = St1::Item;
fn poll_next(
mut self: PinMut<Self>,
cx: &mut task::Context,
) -> Poll<Option<Self::Item>> {
if let Some(first) = self.first().as_pin_mut() {
if let Some(item) = ready!(first.poll_next(cx)) {
return Poll::Ready(Some(item))
}
}
PinMut::set(self.first(), None);
self.second().poll_next(cx)
}
}