ready.rs - source
Description: Source of the Rust file `library/core/src/future/ready.rs`.

#
core/future/
ready.rs

    1use crate::future::Future;
    2use crate::pin::Pin;
    3use crate::task::{Context, Poll};
    4
    5/// A future that is immediately ready with a value.
    6///
    7/// This `struct` is created by [`ready()`]. See its
    8/// documentation for more.
    9#[stable(feature = "future_readiness_fns", since = "1.48.0")]
    10#[derive(Debug, Clone)]
    11#[must_use = "futures do nothing unless you `.await` or poll them"]
    12pub struct Ready<T>(Option<T>);
    13
    14#[stable(feature = "future_readiness_fns", since = "1.48.0")]
    15impl<T> Unpin for Ready<T> {}
    16
    17#[stable(feature = "future_readiness_fns", since = "1.48.0")]
    18impl<T> Future for Ready<T> {
    19    type Output = T;
    20
    21    #[inline]
    22    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<T> {
    23        Poll::Ready(self.0.take().expect("`Ready` polled after completion"))
    24    }
    25}
    26
    27impl<T> Ready<T> {
    28    /// Consumes the `Ready`, returning the wrapped value.
    29    ///
    30    /// # Panics
    31    ///
    32    /// Will panic if this [`Ready`] was already polled to completion.
    33    ///
    34    /// # Examples
    35    ///
    36    /// ```
    37    /// use std::future;
    38    ///
    39    /// let a = future::ready(1);
    40    /// assert_eq!(a.into_inner(), 1);
    41    /// ```
    42    #[stable(feature = "ready_into_inner", since = "1.82.0")]
    43    #[must_use]
    44    #[inline]
    45    pub fn into_inner(self) -> T {
    46        self.0.expect("Called `into_inner()` on `Ready` after completion")
    47    }
    48}
    49
    50/// Creates a future that is immediately ready with a value.
    51///
    52/// Futures created through this function are functionally similar to those
    53/// created through `async {}`. The main difference is that futures created
    54/// through this function are named and implement `Unpin`.
    55///
    56/// # Examples
    57///
    58/// ```
    59/// use std::future;
    60///
    61/// # async fn run() {
    62/// let a = future::ready(1);
    63/// assert_eq!(a.await, 1);
    64/// # }
    65/// ```
    66#[stable(feature = "future_readiness_fns", since = "1.48.0")]
    67pub fn ready<T>(t: T) -> Ready<T> {
    68    Ready(Some(t))
    69}