1 use crate::fns::FnMut1;
2 use core::fmt;
3 use core::pin::Pin;
4 use futures_core::future::Future;
5 use futures_core::ready;
6 use futures_core::stream::{FusedStream, Stream};
7 use futures_core::task::{Context, Poll};
8 #[cfg(feature = "sink")]
9 use futures_sink::Sink;
10 use pin_project_lite::pin_project;
11 
12 pin_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 
27 impl<St, Fut, F> fmt::Debug for Filter<St, Fut, F>
28 where
29     St: Stream + fmt::Debug,
30     St::Item: fmt::Debug,
31     Fut: fmt::Debug,
32 {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result33     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
43 impl<St, Fut, F> Filter<St, Fut, F>
44 where
45     St: Stream,
46     F: for<'a> FnMut1<&'a St::Item, Output = Fut>,
47     Fut: Future<Output = bool>,
48 {
new(stream: St, f: F) -> Self49     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 
56 impl<St, Fut, F> FusedStream for Filter<St, Fut, F>
57 where
58     St: Stream + FusedStream,
59     F: FnMut(&St::Item) -> Fut,
60     Fut: Future<Output = bool>,
61 {
is_terminated(&self) -> bool62     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
68 impl<St, Fut, F> Stream for Filter<St, Fut, F>
69 where
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 
poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>>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 
size_hint(&self) -> (usize, Option<usize>)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")]
108 impl<S, Fut, F, Item> Sink<Item> for Filter<S, Fut, F>
109 where
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