| use core::fmt; |
| use core::pin::Pin; |
| use futures_core::future::{FusedFuture, Future}; |
| use futures_core::stream::Stream; |
| use futures_core::task::{Context, Poll}; |
| use pin_project::{pin_project, project}; |
| |
| /// Future for the [`fold`](super::StreamExt::fold) method. |
| #[pin_project] |
| #[must_use = "futures do nothing unless you `.await` or poll them"] |
| pub struct Fold<St, Fut, T, F> { |
| #[pin] |
| stream: St, |
| f: F, |
| accum: Option<T>, |
| #[pin] |
| future: Option<Fut>, |
| } |
| |
| impl<St, Fut, T, F> fmt::Debug for Fold<St, Fut, T, F> |
| where |
| St: fmt::Debug, |
| Fut: fmt::Debug, |
| T: fmt::Debug, |
| { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Fold") |
| .field("stream", &self.stream) |
| .field("accum", &self.accum) |
| .field("future", &self.future) |
| .finish() |
| } |
| } |
| |
| impl<St, Fut, T, F> Fold<St, Fut, T, F> |
| where St: Stream, |
| F: FnMut(T, St::Item) -> Fut, |
| Fut: Future<Output = T>, |
| { |
| 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> |
| where St: Stream, |
| F: FnMut(T, St::Item) -> Fut, |
| Fut: Future<Output = T>, |
| { |
| 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; |
| |
| #[project] |
| fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> { |
| #[project] |
| let Fold { mut stream, f, accum, mut future } = self.project(); |
| Poll::Ready(loop { |
| if let Some(fut) = future.as_mut().as_pin_mut() { |
| // we're currently processing a future to produce a new accum value |
| *accum = Some(ready!(fut.poll(cx))); |
| future.set(None); |
| } else if accum.is_some() { |
| // we're waiting on a new item from the stream |
| let res = ready!(stream.as_mut().poll_next(cx)); |
| let a = accum.take().unwrap(); |
| if let Some(item) = res { |
| future.set(Some(f(a, item))); |
| } else { |
| break a; |
| } |
| } else { |
| panic!("Fold polled after completion") |
| } |
| }) |
| } |
| } |