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

     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45

    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))
    }