futures_util/future/try_future/
try_flatten_err.rs

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1use core::pin::Pin;
2use futures_core::future::{FusedFuture, Future, TryFuture};
3use futures_core::ready;
4use futures_core::task::{Context, Poll};
5use pin_project_lite::pin_project;
6
7pin_project! {
8    #[project = TryFlattenErrProj]
9    #[derive(Debug)]
10    pub enum TryFlattenErr<Fut1, Fut2> {
11        First { #[pin] f: Fut1 },
12        Second { #[pin] f: Fut2 },
13        Empty,
14    }
15}
16
17impl<Fut1, Fut2> TryFlattenErr<Fut1, Fut2> {
18    pub(crate) fn new(future: Fut1) -> Self {
19        Self::First { f: future }
20    }
21}
22
23impl<Fut> FusedFuture for TryFlattenErr<Fut, Fut::Error>
24where
25    Fut: TryFuture,
26    Fut::Error: TryFuture<Ok = Fut::Ok>,
27{
28    fn is_terminated(&self) -> bool {
29        match self {
30            Self::Empty => true,
31            _ => false,
32        }
33    }
34}
35
36impl<Fut> Future for TryFlattenErr<Fut, Fut::Error>
37where
38    Fut: TryFuture,
39    Fut::Error: TryFuture<Ok = Fut::Ok>,
40{
41    type Output = Result<Fut::Ok, <Fut::Error as TryFuture>::Error>;
42
43    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
44        Poll::Ready(loop {
45            match self.as_mut().project() {
46                TryFlattenErrProj::First { f } => match ready!(f.try_poll(cx)) {
47                    Err(f) => self.set(Self::Second { f }),
48                    Ok(e) => {
49                        self.set(Self::Empty);
50                        break Ok(e);
51                    }
52                },
53                TryFlattenErrProj::Second { f } => {
54                    let output = ready!(f.try_poll(cx));
55                    self.set(Self::Empty);
56                    break output;
57                }
58                TryFlattenErrProj::Empty => panic!("TryFlattenErr polled after completion"),
59            }
60        })
61    }
62}
futures_util/future/try_future/try_flatten_err.rs

futures_util/future/try_future/
try_flatten_err.rs
