async_std/stream/stream/
scan.rs

1use core::pin::Pin;
2
3use pin_project_lite::pin_project;
4
5use crate::stream::Stream;
6use crate::task::{Context, Poll};
7
8pin_project! {
9    /// A stream to maintain state while polling another stream.
10    ///
11    /// This `struct` is created by the [`scan`] method on [`Stream`]. See its
12    /// documentation for more.
13    ///
14    /// [`scan`]: trait.Stream.html#method.scan
15    /// [`Stream`]: trait.Stream.html
16    #[derive(Debug)]
17    pub struct Scan<S, St, F> {
18        #[pin]
19        stream: S,
20        state_f: (St, F),
21    }
22}
23
24impl<S, St, F> Scan<S, St, F> {
25    pub(crate) fn new(stream: S, initial_state: St, f: F) -> Self {
26        Self {
27            stream,
28            state_f: (initial_state, f),
29        }
30    }
31}
32
33impl<S, St, F, B> Stream for Scan<S, St, F>
34where
35    S: Stream,
36    F: FnMut(&mut St, S::Item) -> Option<B>,
37{
38    type Item = B;
39
40    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<B>> {
41        let mut this = self.project();
42        let poll_result = this.stream.as_mut().poll_next(cx);
43        poll_result.map(|item| {
44            item.and_then(|item| {
45                let (state, f) = this.state_f;
46                f(state, item)
47            })
48        })
49    }
50}
async_std/stream/stream/scan.rs

async_std/stream/stream/
scan.rs
