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use crate::stream::{StreamExt, Fuse};
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::stream::Stream;
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Peekable<St: Stream> {
stream: Fuse<St>,
peeked: Option<St::Item>,
}
impl<St: Stream + Unpin> Unpin for Peekable<St> {}
impl<St: Stream> Peekable<St> {
unsafe_pinned!(stream: Fuse<St>);
unsafe_unpinned!(peeked: Option<St::Item>);
pub(super) fn new(stream: St) -> Peekable<St> {
Peekable {
stream: stream.fuse(),
peeked: None
}
}
pub fn peek<'a>(
self: &'a mut Pin<&mut Self>,
lw: &LocalWaker,
) -> Poll<Option<&'a St::Item>> {
if self.peeked().is_some() {
return Poll::Ready(self.peeked().as_ref())
}
match ready!(self.stream().poll_next(lw)) {
None => Poll::Ready(None),
Some(item) => {
*self.peeked() = Some(item);
Poll::Ready(self.peeked().as_ref())
}
}
}
}
impl<S: Stream> Stream for Peekable<S> {
type Item = S::Item;
fn poll_next(
mut self: Pin<&mut Self>,
lw: &LocalWaker
) -> Poll<Option<Self::Item>> {
if let Some(item) = self.peeked().take() {
return Poll::Ready(Some(item))
}
self.stream().poll_next(lw)
}
}