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    /// Extracts the successful type of a `Poll<T>`.
    ///
    /// This macro bakes in propagation of `Pending` signals by returning early.
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(future_readiness_fns)]
    /// #![feature(ready_macro)]
    ///
    /// use core::task::{ready, Context, Poll};
    /// use core::future::{self, Future};
    /// use core::pin::Pin;
    ///
    /// pub fn do_poll(cx: &mut Context<'_>) -> Poll<()> {
    ///     let mut fut = future::ready(42);
    ///     let fut = Pin::new(&mut fut);
    ///
    ///     let num = ready!(fut.poll(cx));
    ///     # drop(num);
    ///     // ... use num
    ///
    ///     Poll::Ready(())
    /// }
    /// ```
    ///
    /// The `ready!` call expands to:
    ///
    /// ```
    /// # #![feature(future_readiness_fns)]
    /// # #![feature(ready_macro)]
    /// #
    /// # use core::task::{Context, Poll};
    /// # use core::future::{self, Future};
    /// # use core::pin::Pin;
    /// #
    /// # pub fn do_poll(cx: &mut Context<'_>) -> Poll<()> {
    ///     # let mut fut = future::ready(42);
    ///     # let fut = Pin::new(&mut fut);
    ///     #
    /// let num = match fut.poll(cx) {
    ///     Poll::Ready(t) => t,
    ///     Poll::Pending => return Poll::Pending,
    /// };
    ///     # drop(num);
    ///     # // ... use num
    ///     #
    ///     # Poll::Ready(())
    /// # }
    /// ```
    #[unstable(feature = "ready_macro", issue = "70922")]
    #[rustc_macro_transparency = "semitransparent"]
    pub macro ready($e:expr) {
        match $e {
            $crate::task::Poll::Ready(t) => t,
            $crate::task::Poll::Pending => {
                return $crate::task::Poll::Pending;
            }
        }
    }