blob: bb2e8fb9743b52523f2db2e91de3d8d8f679fd6d [file] [log] [blame]
use core::marker::Unpin;
use core::pin::PinMut;
use futures_core::future::Future;
use futures_core::stream::Stream;
use futures_core::task::{self, 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> 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: PinMut<Self>, cx: &mut task::Context) -> Poll<T> {
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().poll(cx));
*self.accum() = Some(accum);
PinMut::set(self.future(), None);
}
let item = ready!(self.stream().poll_next(cx));
let accum = self.accum().take()
.expect("Fold polled after completion");
if let Some(e) = item {
let future = (self.f())(accum, e);
PinMut::set(self.future(), Some(future));
} else {
return Poll::Ready(accum)
}
}
}
}