blob: dadf833b00f4a505250d3c50059421a7b1bcbaf2 [file] [log] [blame]
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::future::{FusedFuture, Future, TryFuture};
use futures_core::stream::TryStream;
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// The future for the `TryStream::fold` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct TryFold<St, Fut, T, F> {
stream: St,
f: F,
accum: Option<T>,
future: Option<Fut>,
}
impl<St: Unpin, Fut: Unpin, T, F> Unpin for TryFold<St, Fut, T, F> {}
impl<St, Fut, T, F> TryFold<St, Fut, T, F>
where St: TryStream,
F: FnMut(T, St::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = St::Error>,
{
unsafe_pinned!(stream: St);
unsafe_unpinned!(f: F);
unsafe_unpinned!(accum: Option<T>);
unsafe_pinned!(future: Option<Fut>);
pub(super) fn new(stream: St, f: F, t: T) -> TryFold<St, Fut, T, F> {
TryFold {
stream,
f,
accum: Some(t),
future: None,
}
}
}
impl<St, Fut, T, F> FusedFuture for TryFold<St, Fut, T, F> {
fn is_terminated(&self) -> bool {
self.accum.is_none() && self.future.is_none()
}
}
impl<St, Fut, T, F> Future for TryFold<St, Fut, T, F>
where St: TryStream,
F: FnMut(T, St::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = St::Error>,
{
type Output = Result<T, St::Error>;
fn poll(mut self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Self::Output> {
loop {
// we're currently processing a future to produce a new accum value
if self.as_mut().accum().is_none() {
let accum = match ready!(
self.as_mut().future().as_pin_mut()
.expect("TryFold polled after completion")
.try_poll(lw)
) {
Ok(accum) => accum,
Err(e) => {
// Indicate that the future can no longer be polled.
self.as_mut().future().set(None);
return Poll::Ready(Err(e));
}
};
*self.as_mut().accum() = Some(accum);
self.as_mut().future().set(None);
}
let item = match ready!(self.as_mut().stream().try_poll_next(lw)) {
Some(Ok(item)) => Some(item),
Some(Err(e)) => {
// Indicate that the future can no longer be polled.
*self.as_mut().accum() = None;
return Poll::Ready(Err(e));
}
None => None,
};
let accum = self.as_mut().accum().take().unwrap();
if let Some(e) = item {
let future = (self.as_mut().f())(accum, e);
self.as_mut().future().set(Some(future));
} else {
return Poll::Ready(Ok(accum))
}
}
}
}