forked from mirror/async-std
68 lines
1.4 KiB
Rust
68 lines
1.4 KiB
Rust
use core::marker::PhantomData;
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use core::pin::Pin;
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use core::task::{Context, Poll};
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use crate::stream::{DoubleEndedStream, ExactSizeStream, FusedStream, Stream};
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/// A stream that never returns any items.
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///
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/// This stream is created by the [`pending`] function. See its
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/// documentation for more.
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///
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/// [`pending`]: fn.pending.html
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#[derive(Debug)]
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pub struct Pending<T> {
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_marker: PhantomData<T>,
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}
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/// Creates a stream that never returns any items.
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///
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/// The returned stream will always return `Pending` when polled.
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/// # Examples
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///
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/// ```
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/// # async_std::task::block_on(async {
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/// #
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/// use std::time::Duration;
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///
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/// use async_std::prelude::*;
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/// use async_std::stream;
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///
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/// let dur = Duration::from_millis(100);
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/// let mut s = stream::pending::<()>().timeout(dur);
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///
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/// let item = s.next().await;
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///
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/// assert!(item.is_some());
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/// assert!(item.unwrap().is_err());
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///
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/// #
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/// # })
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/// ```
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pub fn pending<T>() -> Pending<T> {
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Pending {
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_marker: PhantomData,
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}
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}
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impl<T> Stream for Pending<T> {
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type Item = T;
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fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<T>> {
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Poll::Pending
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}
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}
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impl<T> DoubleEndedStream for Pending<T> {
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fn poll_next_back(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<T>> {
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Poll::Pending
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}
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}
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impl<T> FusedStream for Pending<T> {}
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impl<T> ExactSizeStream for Pending<T> {
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fn len(&self) -> usize {
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0
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}
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}
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