forked from mirror/async-std
48 lines
987 B
Rust
48 lines
987 B
Rust
use std::pin::Pin;
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use pin_project_lite::pin_project;
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use crate::stream::Stream;
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use crate::task::{Context, Poll};
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/// Creates a stream that yields a single item.
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///
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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 async_std::prelude::*;
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/// use async_std::stream;
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///
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/// let mut s = stream::once(7);
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///
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/// assert_eq!(s.next().await, Some(7));
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/// assert_eq!(s.next().await, None);
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/// #
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/// # })
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/// ```
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pub fn once<T>(t: T) -> Once<T> {
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Once { value: Some(t) }
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}
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pin_project! {
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/// A stream that yields a single item.
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///
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/// This stream is created by the [`once`] function. See its
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/// documentation for more.
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///
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/// [`once`]: fn.once.html
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#[derive(Debug)]
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pub struct Once<T> {
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value: Option<T>,
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}
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}
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impl<T: Unpin> Stream for Once<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::Ready(self.project().value.take())
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}
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}
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