1 files changed, 45 insertions, 0 deletions
diff --git a/library/core/src/future/ready.rs b/library/core/src/future/ready.rs
new file mode 100644
index 00000000000..31b39d7fb6c
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+++ b/library/core/src/future/ready.rs
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+use crate::future::Future;
+use crate::pin::Pin;
+use crate::task::{Context, Poll};
+
+/// Creates a future that is immediately ready with a value.
+///
+/// This `struct` is created by the [`ready`] function. See its
+/// documentation for more.
+///
+/// [`ready`]: fn.ready.html
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+#[derive(Debug, Clone)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Ready<T>(Option<T>);
+
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+impl<T> Unpin for Ready<T> {}
+
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+impl<T> Future for Ready<T> {
+    type Output = T;
+
+    #[inline]
+    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<T> {
+        Poll::Ready(self.0.take().expect("Ready polled after completion"))
+    }
+}
+
+/// Creates a future that is immediately ready with a value.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(future_readiness_fns)]
+/// use core::future;
+///
+/// # async fn run() {
+/// let a = future::ready(1);
+/// assert_eq!(a.await, 1);
+/// # }
+/// ```
+#[unstable(feature = "future_readiness_fns", issue = "70921")]
+pub fn ready<T>(t: T) -> Ready<T> {
+    Ready(Some(t))
+}