1use crate::Stream;
2
3use core::fmt;
4use core::pin::Pin;
5use core::task::{Context, Poll};
6use pin_project_lite::pin_project;
7
8pin_project! {
9 /// Stream for the [`map_while`](super::StreamExt::map_while) method.
10 #[must_use = "streams do nothing unless polled"]
11 pub struct MapWhile<St, F> {
12 #[pin]
13 stream: St,
14 f: F,
15 }
16}
17
18impl<St, F> fmt::Debug for MapWhile<St, F>
19where
20 St: fmt::Debug,
21{
22 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
23 f.debug_struct("MapWhile")
24 .field("stream", &self.stream)
25 .finish()
26 }
27}
28
29impl<St, F> MapWhile<St, F> {
30 pub(super) fn new(stream: St, f: F) -> Self {
31 MapWhile { stream, f }
32 }
33}
34
35impl<St, F, T> Stream for MapWhile<St, F>
36where
37 St: Stream,
38 F: FnMut(St::Item) -> Option<T>,
39{
40 type Item = T;
41
42 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
43 let me = self.project();
44 let f = me.f;
45 me.stream.poll_next(cx).map(|opt| opt.and_then(f))
46 }
47
48 fn size_hint(&self) -> (usize, Option<usize>) {
49 let (_, upper) = self.stream.size_hint();
50 (0, upper)
51 }
52}
53