1 use crate::Stream; 2 3 use core::future::Future; 4 use core::marker::PhantomPinned; 5 use core::pin::Pin; 6 use core::task::{Context, Poll}; 7 use pin_project_lite::pin_project; 8 9 pin_project! { 10 /// Future for the [`next`](super::StreamExt::next) method. 11 /// 12 /// # Cancel safety 13 /// 14 /// This method is cancel safe. It only 15 /// holds onto a reference to the underlying stream, 16 /// so dropping it will never lose a value. 17 /// 18 #[derive(Debug)] 19 #[must_use = "futures do nothing unless you `.await` or poll them"] 20 pub struct Next<'a, St: ?Sized> { 21 stream: &'a mut St, 22 // Make this future `!Unpin` for compatibility with async trait methods. 23 #[pin] 24 _pin: PhantomPinned, 25 } 26 } 27 28 impl<'a, St: ?Sized> Next<'a, St> { new(stream: &'a mut St) -> Self29 pub(super) fn new(stream: &'a mut St) -> Self { 30 Next { 31 stream, 32 _pin: PhantomPinned, 33 } 34 } 35 } 36 37 impl<St: ?Sized + Stream + Unpin> Future for Next<'_, St> { 38 type Output = Option<St::Item>; 39 poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>40 fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { 41 let me = self.project(); 42 Pin::new(me.stream).poll_next(cx) 43 } 44 } 45