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&mut DebugStruct<'_, '_>.debug_struct("Filter")
35 .field("stream", &self.stream)
36 .field("pending_fut", &self.pending_fut)
37 .field(name:"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> dynFnMut1<&'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> dynFnMut1<&'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}
118