tokio_stream/stream_ext/
map_while.rs

1use crate::Stream;
2
3use core::fmt;
4use core::pin::Pin;
5use core::task::{Context, Poll};
6use futures_core::FusedStream;
7use pin_project_lite::pin_project;
8
9pin_project! {
10    /// Stream for the [`map_while`](super::StreamExt::map_while) method.
11    #[must_use = "streams do nothing unless polled"]
12    pub struct MapWhile<St, F> {
13        #[pin]
14        stream: St,
15        f: F,
16        done: bool,
17    }
18}
19
20impl<St, F> fmt::Debug for MapWhile<St, F>
21where
22    St: fmt::Debug,
23{
24    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
25        f.debug_struct("MapWhile")
26            .field("stream", &self.stream)
27            .field("done", &self.done)
28            .finish()
29    }
30}
31
32impl<St, F> MapWhile<St, F> {
33    pub(super) fn new(stream: St, f: F) -> Self {
34        MapWhile {
35            stream,
36            f,
37            done: false,
38        }
39    }
40}
41
42impl<St, F, T> Stream for MapWhile<St, F>
43where
44    St: Stream,
45    F: FnMut(St::Item) -> Option<T>,
46{
47    type Item = T;
48
49    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
50        let me = self.project();
51        if *me.done {
52            return Poll::Ready(None);
53        }
54
55        let f = me.f;
56        let done = me.done;
57        me.stream.poll_next(cx).map(|opt| {
58            let mapped = opt.and_then(f);
59            if mapped.is_none() {
60                *done = true;
61            }
62            mapped
63        })
64    }
65
66    fn size_hint(&self) -> (usize, Option<usize>) {
67        if self.done {
68            return (0, Some(0));
69        }
70
71        let (_, upper) = self.stream.size_hint();
72        (0, upper)
73    }
74}
75
76impl<St, F> FusedStream for MapWhile<St, F>
77where
78    Self: Stream,
79{
80    fn is_terminated(&self) -> bool {
81        self.done
82    }
83}
tokio_stream/stream_ext/map_while.rs

tokio_stream/stream_ext/
map_while.rs
