1use core::fmt;
2use core::pin::Pin;
3use futures_core::future::Future;
4use futures_core::ready;
5use futures_core::stream::{FusedStream, Stream};
6use futures_core::task::{Context, Poll};
7#[cfg(feature = "sink")]
8use futures_sink::Sink;
9use pin_project_lite::pin_project;
10
11pin_project! {
12 /// Stream for the [`skip_while`](super::StreamExt::skip_while) method.
13 #[must_use = "streams do nothing unless polled"]
14 pub struct SkipWhile<St, Fut, F> where St: Stream {
15 #[pin]
16 stream: St,
17 f: F,
18 #[pin]
19 pending_fut: Option<Fut>,
20 pending_item: Option<St::Item>,
21 done_skipping: bool,
22 }
23}
24
25impl<St, Fut, F> fmt::Debug for SkipWhile<St, Fut, F>
26where
27 St: Stream + fmt::Debug,
28 St::Item: fmt::Debug,
29 Fut: fmt::Debug,
30{
31 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
32 f.debug_struct("SkipWhile")
33 .field("stream", &self.stream)
34 .field("pending_fut", &self.pending_fut)
35 .field("pending_item", &self.pending_item)
36 .field("done_skipping", &self.done_skipping)
37 .finish()
38 }
39}
40
41impl<St, Fut, F> SkipWhile<St, Fut, F>
42where
43 St: Stream,
44 F: FnMut(&St::Item) -> Fut,
45 Fut: Future<Output = bool>,
46{
47 pub(super) fn new(stream: St, f: F) -> Self {
48 Self { stream, f, pending_fut: None, pending_item: None, done_skipping: false }
49 }
50
51 delegate_access_inner!(stream, St, ());
52}
53
54impl<St, Fut, F> FusedStream for SkipWhile<St, Fut, F>
55where
56 St: FusedStream,
57 F: FnMut(&St::Item) -> Fut,
58 Fut: Future<Output = bool>,
59{
60 fn is_terminated(&self) -> bool {
61 self.pending_item.is_none() && self.stream.is_terminated()
62 }
63}
64
65impl<St, Fut, F> Stream for SkipWhile<St, Fut, F>
66where
67 St: Stream,
68 F: FnMut(&St::Item) -> Fut,
69 Fut: Future<Output = bool>,
70{
71 type Item = St::Item;
72
73 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> {
74 let mut this = self.project();
75
76 if *this.done_skipping {
77 return this.stream.poll_next(cx);
78 }
79
80 Poll::Ready(loop {
81 if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
82 let skipped = ready!(fut.poll(cx));
83 let item = this.pending_item.take();
84 this.pending_fut.set(None);
85 if !skipped {
86 *this.done_skipping = true;
87 break item;
88 }
89 } else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
90 this.pending_fut.set(Some((this.f)(&item)));
91 *this.pending_item = Some(item);
92 } else {
93 break None;
94 }
95 })
96 }
97
98 fn size_hint(&self) -> (usize, Option<usize>) {
99 if self.done_skipping {
100 self.stream.size_hint()
101 } else {
102 let pending_len = usize::from(self.pending_item.is_some());
103 let (_, upper) = self.stream.size_hint();
104 let upper = match upper {
105 Some(x) => x.checked_add(pending_len),
106 None => None,
107 };
108 (0, upper) // can't know a lower bound, due to the predicate
109 }
110 }
111}
112
113// Forwarding impl of Sink from the underlying stream
114#[cfg(feature = "sink")]
115impl<S, Fut, F, Item> Sink<Item> for SkipWhile<S, Fut, F>
116where
117 S: Stream + Sink<Item>,
118 F: FnMut(&S::Item) -> Fut,
119 Fut: Future<Output = bool>,
120{
121 type Error = S::Error;
122
123 delegate_sink!(stream, Item);
124}
125