futures_util/stream/try_stream/
try_fold.rs

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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.debug_struct("TryFold")
30            .field("stream", &self.stream)
31            .field("accum", &self.accum)
32            .field("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}
futures_util/stream/try_stream/try_fold.rs

futures_util/stream/try_stream/
try_fold.rs
