futures_util/stream/try_stream/
and_then.rs

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1use core::fmt;
2use core::pin::Pin;
3use futures_core::future::TryFuture;
4use futures_core::ready;
5use futures_core::stream::{FusedStream, Stream, TryStream};
6use futures_core::task::{Context, Poll};
7#[cfg(feature = "sink")]
8use futures_sink::Sink;
9use pin_project_lite::pin_project;
10
11pin_project! {
12    /// Stream for the [`and_then`](super::TryStreamExt::and_then) method.
13    #[must_use = "streams do nothing unless polled"]
14    pub struct AndThen<St, Fut, F> {
15        #[pin]
16        stream: St,
17        #[pin]
18        future: Option<Fut>,
19        f: F,
20    }
21}
22
23impl<St, Fut, F> fmt::Debug for AndThen<St, Fut, F>
24where
25    St: fmt::Debug,
26    Fut: fmt::Debug,
27{
28    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
29        f.debug_struct("AndThen")
30            .field("stream", &self.stream)
31            .field("future", &self.future)
32            .finish()
33    }
34}
35
36impl<St, Fut, F> AndThen<St, Fut, F>
37where
38    St: TryStream,
39    F: FnMut(St::Ok) -> Fut,
40    Fut: TryFuture<Error = St::Error>,
41{
42    pub(super) fn new(stream: St, f: F) -> Self {
43        Self { stream, future: None, f }
44    }
45
46    delegate_access_inner!(stream, St, ());
47}
48
49impl<St, Fut, F> Stream for AndThen<St, Fut, F>
50where
51    St: TryStream,
52    F: FnMut(St::Ok) -> Fut,
53    Fut: TryFuture<Error = St::Error>,
54{
55    type Item = Result<Fut::Ok, St::Error>;
56
57    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
58        let mut this = self.project();
59
60        Poll::Ready(loop {
61            if let Some(fut) = this.future.as_mut().as_pin_mut() {
62                let item = ready!(fut.try_poll(cx));
63                this.future.set(None);
64                break Some(item);
65            } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
66                this.future.set(Some((this.f)(item)));
67            } else {
68                break None;
69            }
70        })
71    }
72
73    fn size_hint(&self) -> (usize, Option<usize>) {
74        let future_len = usize::from(self.future.is_some());
75        let (lower, upper) = self.stream.size_hint();
76        let lower = lower.saturating_add(future_len);
77        let upper = match upper {
78            Some(x) => x.checked_add(future_len),
79            None => None,
80        };
81        (lower, upper)
82    }
83}
84
85impl<St, Fut, F> FusedStream for AndThen<St, Fut, F>
86where
87    St: TryStream + FusedStream,
88    F: FnMut(St::Ok) -> Fut,
89    Fut: TryFuture<Error = St::Error>,
90{
91    fn is_terminated(&self) -> bool {
92        self.future.is_none() && self.stream.is_terminated()
93    }
94}
95
96// Forwarding impl of Sink from the underlying stream
97#[cfg(feature = "sink")]
98impl<S, Fut, F, Item> Sink<Item> for AndThen<S, Fut, F>
99where
100    S: Sink<Item>,
101{
102    type Error = S::Error;
103
104    delegate_sink!(stream, Item);
105}
futures_util/stream/try_stream/and_then.rs

futures_util/stream/try_stream/
and_then.rs
