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Add stream::pending::{pending, Pending}

This commit is contained in:
Qifan Lu 2019-12-10 18:18:15 -08:00 committed by k-nasa
parent 5d5064b871
commit f8dd3d9816
2 changed files with 51 additions and 0 deletions

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@ -325,6 +325,7 @@ cfg_unstable! {
mod fused_stream;
mod interval;
mod into_stream;
mod pending;
mod product;
mod successors;
mod sum;
@ -336,6 +337,7 @@ cfg_unstable! {
pub use fused_stream::FusedStream;
pub use interval::{interval, Interval};
pub use into_stream::IntoStream;
pub use pending::{pending, Pending};
pub use product::Product;
pub use stream::Merge;
pub use successors::{successors, Successors};

49
src/stream/pending.rs Normal file
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@ -0,0 +1,49 @@
use std::marker::PhantomData;
use std::pin::Pin;
use std::task::{Context, Poll};
use crate::stream::{Stream, DoubleEndedStream, ExactSizeStream, FusedStream};
/// A stream that never returns any items.
///
/// This stream is created by the [`pending`] function. See its
/// documentation for more.
///
/// [`pending`]: fn.pending.html
#[derive(Debug)]
pub struct Pending<T> {
_marker: PhantomData<T>
}
/// Creates a stream that never returns any items.
///
/// The returned stream will always return `Pending` when polled.
pub fn pending<T>() -> Pending<T> {
Pending { _marker: PhantomData }
}
impl<T> Stream for Pending<T> {
type Item = T;
fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<T>> {
Poll::Pending
}
fn size_hint(&self) -> (usize, Option<usize>) {
(0, Some(0))
}
}
impl<T> DoubleEndedStream for Pending<T> {
fn poll_next_back(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<T>> {
Poll::Pending
}
}
impl<T> FusedStream for Pending<T> {}
impl<T> ExactSizeStream for Pending<T> {
fn len(&self) -> usize {
0
}
}