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use core::mem;
use core::pin::Pin;
use futures_core::future::{FusedFuture, Future};
use futures_core::ready;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
use pin_project_lite::pin_project;
pin_project! {
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct Unzip<St, FromA, FromB> {
#[pin]
stream: St,
left: FromA,
right: FromB,
}
}
impl<St: Stream, FromA: Default, FromB: Default> Unzip<St, FromA, FromB> {
fn finish(self: Pin<&mut Self>) -> (FromA, FromB) {
let this = self.project();
(
mem::replace(this.left, Default::default()),
mem::replace(this.right, Default::default()),
)
}
pub(super) fn new(stream: St) -> Self {
Self {
stream,
left: Default::default(),
right: Default::default(),
}
}
}
impl<St, A, B, FromA, FromB> FusedFuture for Unzip<St, FromA, FromB>
where St: FusedStream<Item = (A, B)>,
FromA: Default + Extend<A>,
FromB: Default + Extend<B>,
{
fn is_terminated(&self) -> bool {
self.stream.is_terminated()
}
}
impl<St, A, B, FromA, FromB> Future for Unzip<St, FromA, FromB>
where St: Stream<Item = (A, B)>,
FromA: Default + Extend<A>,
FromB: Default + Extend<B>,
{
type Output = (FromA, FromB);
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<(FromA, FromB)> {
let mut this = self.as_mut().project();
loop {
match ready!(this.stream.as_mut().poll_next(cx)) {
Some(e) => {
this.left.extend(Some(e.0));
this.right.extend(Some(e.1));
},
None => return Poll::Ready(self.finish()),
}
}
}
}