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pub use std::{future::Future, pin::Pin, task::Poll};
pub use futures_util_fork::{maybe_done, poll_fn, MaybeDone, PollFn};
pub use crate::utils::thread_rng_n;
mod futures_util_fork {
use core::{fmt, mem, pin::Pin};
use std::{
future::Future,
task::{Context, Poll},
};
/// Future for the [`poll_fn`] function.
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct PollFn<F> {
f: F,
}
impl<F> Unpin for PollFn<F> {}
/// Creates a new future wrapping around a function returning [`Poll`].
///
/// Polling the returned future delegates to the wrapped function.
///
/// # Examples
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::{
/// future::poll_fn,
/// task::{Context, Poll},
/// };
///
/// fn read_line(_cx: &mut Context<'_>) -> Poll<String> {
/// Poll::Ready("Hello, World!".into())
/// }
///
/// let read_future = poll_fn(read_line);
/// assert_eq!(read_future.await, "Hello, World!".to_owned());
/// # });
/// ```
pub fn poll_fn<T, F>(f: F) -> PollFn<F>
where
F: FnMut(&mut Context<'_>) -> Poll<T>,
{
PollFn { f }
}
impl<F> fmt::Debug for PollFn<F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("PollFn").finish()
}
}
impl<T, F> Future for PollFn<F>
where
F: FnMut(&mut Context<'_>) -> Poll<T>,
{
type Output = T;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
(self.f)(cx)
}
}
/// A future that may have completed.
///
/// This is created by the [`maybe_done()`] function.
#[derive(Debug)]
pub enum MaybeDone<Fut: Future> {
/// A not-yet-completed future
Future(/* #[pin] */ Fut),
/// The output of the completed future
Done(Fut::Output),
/// The empty variant after the result of a [`MaybeDone`] has been
/// taken using the [`take_output`](MaybeDone::take_output) method.
Gone,
}
impl<Fut: Future + Unpin> Unpin for MaybeDone<Fut> {}
/// Wraps a future into a `MaybeDone`
///
/// # Examples
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::{future, pin_mut};
///
/// let future = future::maybe_done(async { 5 });
/// pin_mut!(future);
/// assert_eq!(future.as_mut().take_output(), None);
/// let () = future.as_mut().await;
/// assert_eq!(future.as_mut().take_output(), Some(5));
/// assert_eq!(future.as_mut().take_output(), None);
/// # });
/// ```
pub fn maybe_done<Fut: Future>(future: Fut) -> MaybeDone<Fut> {
MaybeDone::Future(future)
}
impl<Fut: Future> MaybeDone<Fut> {
/// Returns an [`Option`] containing a mutable reference to the output
/// of the future. The output of this method will be [`Some`] if
/// and only if the inner future has been completed and
/// [`take_output`](MaybeDone::take_output) has not yet been
/// called.
#[inline]
pub fn output_mut(self: Pin<&mut Self>) -> Option<&mut Fut::Output> {
unsafe {
match self.get_unchecked_mut() {
MaybeDone::Done(res) => Some(res),
_ => None,
}
}
}
/// Attempt to take the output of a `MaybeDone` without driving it
/// towards completion.
#[inline]
pub fn take_output(self: Pin<&mut Self>) -> Option<Fut::Output> {
match &*self {
Self::Done(_) => {}
Self::Future(_) | Self::Gone => return None,
}
unsafe {
match mem::replace(self.get_unchecked_mut(), Self::Gone) {
MaybeDone::Done(output) => Some(output),
_ => unreachable!(),
}
}
}
}
impl<Fut: Future> Future for MaybeDone<Fut> {
type Output = ();
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
unsafe {
match self.as_mut().get_unchecked_mut() {
MaybeDone::Future(f) => {
let res = ready!(Pin::new_unchecked(f).poll(cx));
self.set(Self::Done(res));
}
MaybeDone::Done(_) => {}
MaybeDone::Gone => panic!("MaybeDone polled after value taken"),
}
}
Poll::Ready(())
}
}
}