ready.rs.html -- source
Description: Source to the Rust file `library/core/src/future/ready.rs`.
Keywords: rust, rustlang, rust-lang

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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 [`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 core::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))
    }