69 lines
1.9 KiB
Rust
69 lines
1.9 KiB
Rust
use crate::future::Future;
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use crate::pin::Pin;
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use crate::task::{Context, Poll};
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/// A future that is immediately ready with a value.
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///
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/// This `struct` is created by [`ready()`]. See its
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/// documentation for more.
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#[stable(feature = "future_readiness_fns", since = "1.48.0")]
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#[derive(Debug, Clone)]
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#[must_use = "futures do nothing unless you `.await` or poll them"]
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pub struct Ready<T>(Option<T>);
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#[stable(feature = "future_readiness_fns", since = "1.48.0")]
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impl<T> Unpin for Ready<T> {}
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#[stable(feature = "future_readiness_fns", since = "1.48.0")]
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impl<T> Future for Ready<T> {
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type Output = T;
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#[inline]
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fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<T> {
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Poll::Ready(self.0.take().expect("`Ready` polled after completion"))
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}
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}
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impl<T> Ready<T> {
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/// Consumes the `Ready`, returning the wrapped value.
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///
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/// # Panics
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///
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/// Will panic if this [`Ready`] was already polled to completion.
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///
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/// # Examples
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///
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/// ```
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/// use std::future;
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///
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/// let a = future::ready(1);
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/// assert_eq!(a.into_inner(), 1);
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/// ```
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#[stable(feature = "ready_into_inner", since = "1.82.0")]
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#[must_use]
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#[inline]
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pub fn into_inner(self) -> T {
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self.0.expect("Called `into_inner()` on `Ready` after completion")
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}
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}
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/// Creates a future that is immediately ready with a value.
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///
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/// Futures created through this function are functionally similar to those
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/// created through `async {}`. The main difference is that futures created
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/// through this function are named and implement `Unpin`.
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///
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/// # Examples
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///
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/// ```
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/// use std::future;
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///
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/// # async fn run() {
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/// let a = future::ready(1);
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/// assert_eq!(a.await, 1);
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/// # }
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/// ```
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#[stable(feature = "future_readiness_fns", since = "1.48.0")]
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pub fn ready<T>(t: T) -> Ready<T> {
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Ready(Some(t))
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}
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