futures_util/stream/stream/
filter.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`](super::StreamExt::filter) method.
14    #[must_use = "streams do nothing unless polled"]
15    pub struct Filter<St, Fut, F>
16        where St: Stream,
17    {
18        #[pin]
19        stream: St,
20        f: F,
21        #[pin]
22        pending_fut: Option<Fut>,
23        pending_item: Option<St::Item>,
24    }
25}
26
27impl<St, Fut, F> fmt::Debug for Filter<St, Fut, F>
28where
29    St: Stream + fmt::Debug,
30    St::Item: fmt::Debug,
31    Fut: fmt::Debug,
32{
33    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
34        f.debug_struct("Filter")
35            .field("stream", &self.stream)
36            .field("pending_fut", &self.pending_fut)
37            .field("pending_item", &self.pending_item)
38            .finish()
39    }
40}
41
42#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
43impl<St, Fut, F> Filter<St, Fut, F>
44where
45    St: Stream,
46    F: for<'a> FnMut1<&'a St::Item, Output = Fut>,
47    Fut: Future<Output = bool>,
48{
49    pub(super) fn new(stream: St, f: F) -> Self {
50        Self { stream, f, pending_fut: None, pending_item: None }
51    }
52
53    delegate_access_inner!(stream, St, ());
54}
55
56impl<St, Fut, F> FusedStream for Filter<St, Fut, F>
57where
58    St: Stream + FusedStream,
59    F: FnMut(&St::Item) -> Fut,
60    Fut: Future<Output = bool>,
61{
62    fn is_terminated(&self) -> bool {
63        self.pending_fut.is_none() && self.stream.is_terminated()
64    }
65}
66
67#[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
68impl<St, Fut, F> Stream for Filter<St, Fut, F>
69where
70    St: Stream,
71    F: for<'a> FnMut1<&'a St::Item, Output = Fut>,
72    Fut: Future<Output = bool>,
73{
74    type Item = St::Item;
75
76    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
77        let mut this = self.project();
78        Poll::Ready(loop {
79            if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
80                let res = ready!(fut.poll(cx));
81                this.pending_fut.set(None);
82                if res {
83                    break this.pending_item.take();
84                }
85                *this.pending_item = None;
86            } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
87                this.pending_fut.set(Some(this.f.call_mut(&item)));
88                *this.pending_item = Some(item);
89            } else {
90                break None;
91            }
92        })
93    }
94
95    fn size_hint(&self) -> (usize, Option<usize>) {
96        let pending_len = usize::from(self.pending_item.is_some());
97        let (_, upper) = self.stream.size_hint();
98        let upper = match upper {
99            Some(x) => x.checked_add(pending_len),
100            None => None,
101        };
102        (0, upper) // can't know a lower bound, due to the predicate
103    }
104}
105
106// Forwarding impl of Sink from the underlying stream
107#[cfg(feature = "sink")]
108impl<S, Fut, F, Item> Sink<Item> for Filter<S, Fut, F>
109where
110    S: Stream + Sink<Item>,
111    F: FnMut(&S::Item) -> Fut,
112    Fut: Future<Output = bool>,
113{
114    type Error = S::Error;
115
116    delegate_sink!(stream, Item);
117}
futures_util/stream/stream/filter.rs

futures_util/stream/stream/
filter.rs
