blob: b3ac394722d6efed84012a57062108d4c018d712 [file] [log] [blame]
use core::marker::Unpin;
use core::mem::PinMut;
use futures_core::future::{Future, TryFuture};
use futures_core::stream::TryStream;
use futures_core::task::{self, 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> 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: PinMut<Self>, cx: &mut task::Context) -> Poll<Self::Output> {
loop {
// we're currently processing a future to produce a new accum value
if self.accum().is_none() {
let accum = ready!(self.future().as_pin_mut().unwrap().try_poll(cx)?);
*self.accum() = Some(accum);
PinMut::set(self.future(), None);
}
let item = ready!(self.stream().try_poll_next(cx)?);
let accum = self.accum().take()
.expect("TryFold polled after completion");
if let Some(e) = item {
let future = (self.f())(accum, e);
PinMut::set(self.future(), Some(future));
} else {
return Poll::Ready(Ok(accum))
}
}
}
}