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use core::fmt;
use core::pin::Pin;
use futures_core::future::Future;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
#[must_use = "streams do nothing unless polled"]
pub struct FlattenStream<Fut: Future> {
state: State<Fut>
}
impl<Fut: Future> FlattenStream<Fut> {
pub(super) fn new(future: Fut) -> FlattenStream<Fut> {
FlattenStream {
state: State::Future(future)
}
}
}
impl<Fut> fmt::Debug for FlattenStream<Fut>
where Fut: Future + fmt::Debug,
Fut::Output: fmt::Debug,
{
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("FlattenStream")
.field("state", &self.state)
.finish()
}
}
#[derive(Debug)]
enum State<Fut: Future> {
Future(Fut),
Stream(Fut::Output),
}
impl<Fut> FusedStream for FlattenStream<Fut>
where Fut: Future,
Fut::Output: Stream + FusedStream,
{
fn is_terminated(&self) -> bool {
match &self.state {
State::Future(_) => false,
State::Stream(stream) => stream.is_terminated(),
}
}
}
impl<Fut> Stream for FlattenStream<Fut>
where Fut: Future,
Fut::Output: Stream,
{
type Item = <Fut::Output as Stream>::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
loop {
let stream = match &mut unsafe { Pin::get_unchecked_mut(self.as_mut()) }.state {
State::Future(f) => {
match unsafe { Pin::new_unchecked(f) }.poll(cx) {
Poll::Pending => {
return Poll::Pending
},
Poll::Ready(stream) => {
stream
}
}
}
State::Stream(s) => {
return unsafe { Pin::new_unchecked(s) }.poll_next(cx);
}
};
unsafe {
Pin::get_unchecked_mut(self.as_mut()).state = State::Stream(stream);
}
}
}
}