use super::TryJoin as TryJoinTrait;
use crate::utils::iter_pin_mut;
use crate::utils::MaybeDone;
use core::fmt;
use core::future::{Future, IntoFuture};
use core::mem;
use core::pin::Pin;
use core::task::{Context, Poll};
use std::boxed::Box;
use std::vec::Vec;
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct TryJoin<Fut, T, E>
where
Fut: Future<Output = Result<T, E>>,
{
elems: Pin<Box<[MaybeDone<Fut>]>>,
}
impl<Fut, T, E> fmt::Debug for TryJoin<Fut, T, E>
where
Fut: Future<Output = Result<T, E>> + fmt::Debug,
Fut::Output: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_list().entries(self.elems.iter()).finish()
}
}
impl<Fut, T, E> Future for TryJoin<Fut, T, E>
where
T: std::fmt::Debug,
Fut: Future<Output = Result<T, E>>,
{
type Output = Result<Vec<T>, E>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let mut all_done = true;
for mut elem in iter_pin_mut(self.elems.as_mut()) {
if elem.as_mut().poll(cx).is_pending() {
all_done = false
} else if let Some(Err(_)) = elem.as_ref().output() {
return Poll::Ready(Err(elem.take().unwrap().unwrap_err()));
}
}
if all_done {
let mut elems = mem::replace(&mut self.elems, Box::pin([]));
let result = iter_pin_mut(elems.as_mut())
.map(|e| e.take().unwrap())
.collect();
Poll::Ready(result)
} else {
Poll::Pending
}
}
}
impl<Fut, T, E> TryJoinTrait for Vec<Fut>
where
T: std::fmt::Debug,
Fut: IntoFuture<Output = Result<T, E>>,
{
type Output = Vec<T>;
type Error = E;
type Future = TryJoin<Fut::IntoFuture, T, E>;
fn try_join(self) -> Self::Future {
let elems: Box<[_]> = self
.into_iter()
.map(|fut| MaybeDone::new(fut.into_future()))
.collect();
TryJoin {
elems: elems.into(),
}
}
}
#[cfg(test)]
mod test {
use super::*;
use std::future;
use std::io::{self, Error, ErrorKind};
#[test]
fn all_ok() {
futures_lite::future::block_on(async {
let res: io::Result<_> = vec![future::ready(Ok("hello")), future::ready(Ok("world"))]
.try_join()
.await;
assert_eq!(res.unwrap(), vec!["hello", "world"]);
})
}
#[test]
fn one_err() {
futures_lite::future::block_on(async {
let err = Error::new(ErrorKind::Other, "oh no");
let res: io::Result<_> = vec![future::ready(Ok("hello")), future::ready(Err(err))]
.try_join()
.await;
assert_eq!(res.unwrap_err().to_string(), String::from("oh no"));
});
}
}