1use core::fmt;
2use core::pin::Pin;
3use futures_core::future::{FusedFuture, Future, TryFuture};
4use futures_core::ready;
5use futures_core::stream::TryStream;
6use futures_core::task::{Context, Poll};
7use pin_project_lite::pin_project;
8
9pin_project! {
10 /// Future for the [`try_fold`](super::TryStreamExt::try_fold) method.
11 #[must_use = "futures do nothing unless you `.await` or poll them"]
12 pub struct TryFold<St, Fut, T, F> {
13 #[pin]
14 stream: St,
15 f: F,
16 accum: Option<T>,
17 #[pin]
18 future: Option<Fut>,
19 }
20}
21
22impl<St, Fut, T, F> fmt::Debug for TryFold<St, Fut, T, F>
23where
24 St: fmt::Debug,
25 Fut: fmt::Debug,
26 T: fmt::Debug,
27{
28 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
29 f&mut DebugStruct<'_, '_>.debug_struct("TryFold")
30 .field("stream", &self.stream)
31 .field("accum", &self.accum)
32 .field(name:"future", &self.future)
33 .finish()
34 }
35}
36
37impl<St, Fut, T, F> TryFold<St, Fut, T, F>
38where
39 St: TryStream,
40 F: FnMut(T, St::Ok) -> Fut,
41 Fut: TryFuture<Ok = T, Error = St::Error>,
42{
43 pub(super) fn new(stream: St, f: F, t: T) -> Self {
44 Self { stream, f, accum: Some(t), future: None }
45 }
46}
47
48impl<St, Fut, T, F> FusedFuture for TryFold<St, Fut, T, F>
49where
50 St: TryStream,
51 F: FnMut(T, St::Ok) -> Fut,
52 Fut: TryFuture<Ok = T, Error = St::Error>,
53{
54 fn is_terminated(&self) -> bool {
55 self.accum.is_none() && self.future.is_none()
56 }
57}
58
59impl<St, Fut, T, F> Future for TryFold<St, Fut, T, F>
60where
61 St: TryStream,
62 F: FnMut(T, St::Ok) -> Fut,
63 Fut: TryFuture<Ok = T, Error = St::Error>,
64{
65 type Output = Result<T, St::Error>;
66
67 fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
68 let mut this = self.project();
69
70 Poll::Ready(loop {
71 if let Some(fut) = this.future.as_mut().as_pin_mut() {
72 // we're currently processing a future to produce a new accum value
73 let res = ready!(fut.try_poll(cx));
74 this.future.set(None);
75 match res {
76 Ok(a) => *this.accum = Some(a),
77 Err(e) => break Err(e),
78 }
79 } else if this.accum.is_some() {
80 // we're waiting on a new item from the stream
81 let res = ready!(this.stream.as_mut().try_poll_next(cx));
82 let a = this.accum.take().unwrap();
83 match res {
84 Some(Ok(item)) => this.future.set(Some((this.f)(a, item))),
85 Some(Err(e)) => break Err(e),
86 None => break Ok(a),
87 }
88 } else {
89 panic!("Fold polled after completion")
90 }
91 })
92 }
93}
94