blob: 39116946c0da9a39ccb67a161b2fe852e6e8207e [file] [log] [blame]
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::future::{FusedFuture, Future};
use futures_core::stream::Stream;
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A future used to collect all the results of a stream into one generic type.
///
/// This future is returned by the `Stream::fold` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Fold<St, Fut, T, F> {
stream: St,
f: F,
accum: Option<T>,
future: Option<Fut>,
}
impl<St: Unpin, Fut: Unpin, T, F> Unpin for Fold<St, Fut, T, F> {}
impl<St, Fut, T, F> Fold<St, Fut, T, F>
where St: Stream,
F: FnMut(T, St::Item) -> Fut,
Fut: Future<Output = T>,
{
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) -> Fold<St, Fut, T, F> {
Fold {
stream,
f,
accum: Some(t),
future: None,
}
}
}
impl<St, Fut, T, F> FusedFuture for Fold<St, Fut, T, F> {
fn is_terminated(&self) -> bool {
self.accum.is_none() && self.future.is_none()
}
}
impl<St, Fut, T, F> Future for Fold<St, Fut, T, F>
where St: Stream,
F: FnMut(T, St::Item) -> Fut,
Fut: Future<Output = T>,
{
type Output = T;
fn poll(mut self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<T> {
loop {
// we're currently processing a future to produce a new accum value
if self.as_mut().accum().is_none() {
let accum = ready!(self.as_mut().future().as_pin_mut().unwrap().poll(lw));
*self.as_mut().accum() = Some(accum);
self.as_mut().future().set(None);
}
let item = ready!(self.as_mut().stream().poll_next(lw));
let accum = self.as_mut().accum().take()
.expect("Fold polled after completion");
if let Some(e) = item {
let future = (self.as_mut().f())(accum, e);
self.as_mut().future().set(Some(future));
} else {
return Poll::Ready(accum)
}
}
}
}