1 use core::marker; 2 use core::pin::Pin; 3 use futures_core::stream::{FusedStream, Stream}; 4 use futures_core::task::{Context, Poll}; 5 6 /// Stream for the [`pending()`] function. 7 #[derive(Debug)] 8 #[must_use = "streams do nothing unless polled"] 9 pub struct Pending<T> { 10 _data: marker::PhantomData<T>, 11 } 12 13 /// Creates a stream which never returns any elements. 14 /// 15 /// The returned stream will always return `Pending` when polled. pending<T>() -> Pending<T>16pub fn pending<T>() -> Pending<T> { 17 Pending { _data: marker::PhantomData } 18 } 19 20 impl<T> Unpin for Pending<T> {} 21 22 impl<T> FusedStream for Pending<T> { is_terminated(&self) -> bool23 fn is_terminated(&self) -> bool { 24 true 25 } 26 } 27 28 impl<T> Stream for Pending<T> { 29 type Item = T; 30 poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>>31 fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<Self::Item>> { 32 Poll::Pending 33 } 34 size_hint(&self) -> (usize, Option<usize>)35 fn size_hint(&self) -> (usize, Option<usize>) { 36 (0, Some(0)) 37 } 38 } 39