1 files changed, 46 insertions, 0 deletions
diff --git a/library/core/src/future/ready.rs b/library/core/src/future/ready.rs
new file mode 100644
index 000000000..48f20f90a
--- /dev/null
+++ b/library/core/src/future/ready.rs
@@ -0,0 +1,46 @@
+use crate::future::Future;
+use crate::pin::Pin;
+use crate::task::{Context, Poll};
+
+/// A future that is immediately ready with a value.
+///
+/// This `struct` is created by [`ready()`]. See its
+/// documentation for more.
+#[stable(feature = "future_readiness_fns", since = "1.48.0")]
+#[derive(Debug, Clone)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct Ready<T>(Option<T>);
+
+#[stable(feature = "future_readiness_fns", since = "1.48.0")]
+impl<T> Unpin for Ready<T> {}
+
+#[stable(feature = "future_readiness_fns", since = "1.48.0")]
+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.
+///
+/// Futures created through this function are functionally similar to those
+/// created through `async {}`. The main difference is that futures created
+/// through this function are named and implement `Unpin`.
+///
+/// # Examples
+///
+/// ```
+/// use std::future;
+///
+/// # async fn run() {
+/// let a = future::ready(1);
+/// assert_eq!(a.await, 1);
+/// # }
+/// ```
+#[stable(feature = "future_readiness_fns", since = "1.48.0")]
+pub fn ready<T>(t: T) -> Ready<T> {
+    Ready(Some(t))
+}