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use std::pin::Pin;
use std::task::{Context, Poll};
use futures_core::stream::Stream;
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct YieldStream<St, I>
where St: Stream<Item=I>
{
source: St,
yielded: bool,
}
impl<St, I> YieldStream<St, I>
where St: Stream<Item=I>
{
pub fn new(source: St) -> Self {
YieldStream { source, yielded: true }
}
}
impl<St, I> Stream for YieldStream<St, I>
where St: Stream<Item=I>
{
type Item = I;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>)
-> Poll<Option<Self::Item>>
{
let this = unsafe { self.get_unchecked_mut() };
if this.yielded {
let src = unsafe { Pin::new_unchecked(&mut this.source) };
let next = src.poll_next(cx);
if let Poll::Ready(Some(_)) = next {
this.yielded = false;
}
next
} else {
this.yielded = true;
cx.waker().wake_by_ref();
Poll::Pending
}
}
}