1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
|
use tokio_stream::{Stream, StreamExt};
use std::pin::Pin;
use std::task::{Context, Poll};
// a stream which alternates between Some and None
struct Alternate {
state: i32,
}
impl Stream for Alternate {
type Item = i32;
fn poll_next(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<i32>> {
let val = self.state;
self.state += 1;
// if it's even, Some(i32), else None
if val % 2 == 0 {
Poll::Ready(Some(val))
} else {
Poll::Ready(None)
}
}
}
#[tokio::test]
async fn basic_usage() {
let mut stream = Alternate { state: 0 };
// the stream goes back and forth
assert_eq!(stream.next().await, Some(0));
assert_eq!(stream.next().await, None);
assert_eq!(stream.next().await, Some(2));
assert_eq!(stream.next().await, None);
// however, once it is fused
let mut stream = stream.fuse();
assert_eq!(stream.size_hint(), (0, None));
assert_eq!(stream.next().await, Some(4));
assert_eq!(stream.size_hint(), (0, None));
assert_eq!(stream.next().await, None);
// it will always return `None` after the first time.
assert_eq!(stream.size_hint(), (0, Some(0)));
assert_eq!(stream.next().await, None);
assert_eq!(stream.size_hint(), (0, Some(0)));
}
|
