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}
112