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use super::TryJoin as TryJoinTrait;
use crate::utils::MaybeDone;
use core::fmt;
use core::future::{Future, IntoFuture};
use core::pin::Pin;
use core::task::{Context, Poll};
use pin_project::pin_project;
impl<Fut, T, E, const N: usize> TryJoinTrait for [Fut; N]
where
T: std::fmt::Debug,
Fut: IntoFuture<Output = Result<T, E>>,
E: fmt::Debug,
{
type Output = [T; N];
type Error = E;
type Future = TryJoin<Fut::IntoFuture, T, E, N>;
fn try_join(self) -> Self::Future {
TryJoin {
elems: self.map(|fut| MaybeDone::new(fut.into_future())),
}
}
}
#[must_use = "futures do nothing unless you `.await` or poll them"]
#[pin_project]
pub struct TryJoin<Fut, T, E, const N: usize>
where
T: fmt::Debug,
Fut: Future<Output = Result<T, E>>,
{
elems: [MaybeDone<Fut>; N],
}
impl<Fut, T, E, const N: usize> fmt::Debug for TryJoin<Fut, T, E, N>
where
Fut: Future<Output = Result<T, E>> + fmt::Debug,
Fut::Output: fmt::Debug,
T: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Join").field("elems", &self.elems).finish()
}
}
impl<Fut, T, E, const N: usize> Future for TryJoin<Fut, T, E, N>
where
T: fmt::Debug,
Fut: Future<Output = Result<T, E>>,
E: fmt::Debug,
{
type Output = Result<[T; N], E>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let mut all_done = true;
let this = self.project();
for elem in this.elems.iter_mut() {
let mut elem = unsafe { Pin::new_unchecked(elem) };
if let Poll::Pending = elem.as_mut().poll(cx) {
all_done = false
} else if let Some(Err(_)) = elem.as_ref().output() {
return Poll::Ready(Err(elem.take().unwrap().unwrap_err()));
}
}
if all_done {
use core::mem::MaybeUninit;
let mut out: [MaybeUninit<T>; N] = {
unsafe { MaybeUninit::<[MaybeUninit<_>; N]>::uninit().assume_init() }
};
#[allow(clippy::clippy::needless_range_loop)]
for (i, el) in this.elems.iter_mut().enumerate() {
let el = unsafe { Pin::new_unchecked(el) }.take().unwrap().unwrap();
out[i] = MaybeUninit::new(el);
}
let result = unsafe { out.as_ptr().cast::<[T; N]>().read() };
Poll::Ready(Ok(result))
} else {
Poll::Pending
}
}
}
#[cfg(test)]
mod test {
use super::*;
use std::future;
use std::io::{self, Error, ErrorKind};
#[test]
fn all_ok() {
async_io::block_on(async {
let res: io::Result<_> = [future::ready(Ok("hello")), future::ready(Ok("world"))]
.try_join()
.await;
assert_eq!(res.unwrap(), ["hello", "world"]);
})
}
#[test]
fn one_err() {
async_io::block_on(async {
let err = Error::new(ErrorKind::Other, "oh no");
let res: io::Result<_> = [future::ready(Ok("hello")), future::ready(Err(err))]
.try_join()
.await;
assert_eq!(res.unwrap_err().to_string(), String::from("oh no"));
});
}
}