futures_util/stream/stream/
filter_map.rs

1use crate::fns::FnMut1;
2use core::fmt;
3use core::pin::Pin;
4use futures_core::future::Future;
5use futures_core::ready;
6use futures_core::stream::{FusedStream, Stream};
7use futures_core::task::{Context, Poll};
8#[cfg(feature = "sink")]
9use futures_sink::Sink;
10use pin_project_lite::pin_project;
11
12pin_project! {
13    /// Stream for the [`filter_map`](super::StreamExt::filter_map) method.
14    #[must_use = "streams do nothing unless polled"]
15    pub struct FilterMap<St, Fut, F> {
16        #[pin]
17        stream: St,
18        f: F,
19        #[pin]
20        pending: Option<Fut>,
21    }
22}
23
24impl<St, Fut, F> fmt::Debug for FilterMap<St, Fut, F>
25where
26    St: fmt::Debug,
27    Fut: fmt::Debug,
28{
29    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
30        f.debug_struct("FilterMap")
31            .field("stream", &self.stream)
32            .field("pending", &self.pending)
33            .finish()
34    }
35}
36
37impl<St, Fut, F> FilterMap<St, Fut, F>
38where
39    St: Stream,
40    F: FnMut(St::Item) -> Fut,
41    Fut: Future,
42{
43    pub(super) fn new(stream: St, f: F) -> Self {
44        Self { stream, f, pending: None }
45    }
46
47    delegate_access_inner!(stream, St, ());
48}
49
50impl<St, Fut, F, T> FusedStream for FilterMap<St, Fut, F>
51where
52    St: Stream + FusedStream,
53    F: FnMut1<St::Item, Output = Fut>,
54    Fut: Future<Output = Option<T>>,
55{
56    fn is_terminated(&self) -> bool {
57        self.pending.is_none() && self.stream.is_terminated()
58    }
59}
60
61impl<St, Fut, F, T> Stream for FilterMap<St, Fut, F>
62where
63    St: Stream,
64    F: FnMut1<St::Item, Output = Fut>,
65    Fut: Future<Output = Option<T>>,
66{
67    type Item = T;
68
69    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
70        let mut this = self.project();
71        Poll::Ready(loop {
72            if let Some(p) = this.pending.as_mut().as_pin_mut() {
73                // We have an item in progress, poll that until it's done
74                let item = ready!(p.poll(cx));
75                this.pending.set(None);
76                if item.is_some() {
77                    break item;
78                }
79            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
80                // No item in progress, but the stream is still going
81                this.pending.set(Some(this.f.call_mut(item)));
82            } else {
83                // The stream is done
84                break None;
85            }
86        })
87    }
88
89    fn size_hint(&self) -> (usize, Option<usize>) {
90        let pending_len = usize::from(self.pending.is_some());
91        let (_, upper) = self.stream.size_hint();
92        let upper = match upper {
93            Some(x) => x.checked_add(pending_len),
94            None => None,
95        };
96        (0, upper) // can't know a lower bound, due to the predicate
97    }
98}
99
100// Forwarding impl of Sink from the underlying stream
101#[cfg(feature = "sink")]
102impl<S, Fut, F, Item> Sink<Item> for FilterMap<S, Fut, F>
103where
104    S: Stream + Sink<Item>,
105    F: FnMut1<S::Item, Output = Fut>,
106    Fut: Future,
107{
108    type Error = S::Error;
109
110    delegate_sink!(stream, Item);
111}
futures_util/stream/stream/filter_map.rs

futures_util/stream/stream/
filter_map.rs
