src/libcore/future/ready.rs

   1 use crate::future::Future;
   2 use crate::pin::Pin;
   3 use crate::task::{Context, Poll};
   4
   5 /// Creates a future that is immediately ready with a value.
   6 ///
   7 /// This `struct` is created by the [`ready`] function. See its
   8 /// documentation for more.
   9 ///
  10 /// [`ready`]: fn.ready.html
  11 #[unstable(feature = "future_readiness_fns", issue = "70921")]
  12 #[derive(Debug, Clone)]
  13 #[must_use = "futures do nothing unless you `.await` or poll them"]
  14 pub struct Ready<T>(Option<T>);
  15
  16 #[unstable(feature = "future_readiness_fns", issue = "70921")]
  17 impl<T> Unpin for Ready<T> {}
  18
  19 #[unstable(feature = "future_readiness_fns", issue = "70921")]
  20 impl<T> Future for Ready<T> {
  21     type Output = T;
  22
  23     #[inline]
  24     fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<T> {
  25         Poll::Ready(self.0.take().expect("Ready polled after completion"))
  26     }
  27 }
  28
  29 /// Creates a future that is immediately ready with a value.
  30 ///
  31 /// # Examples
  32 ///
  33 /// ```
  34 /// #![feature(future_readiness_fns)]
  35 /// use core::future;
  36 ///
  37 /// # async fn run() {
  38 /// let a = future::ready(1);
  39 /// assert_eq!(a.await, 1);
  40 /// # }
  41 /// ```
  42 #[unstable(feature = "future_readiness_fns", issue = "70921")]
  43 pub fn ready<T>(t: T) -> Ready<T> {
  44     Ready(Some(t))
  45 }