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
51
52
53
54
use core::pin::Pin;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
use pin_utils::unsafe_pinned;
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Chain<St1, St2> {
first: Option<St1>,
second: St2,
}
impl<St1, St2> Chain<St1, St2>
where St1: Stream,
St2: Stream<Item = St1::Item>,
{
unsafe_pinned!(first: Option<St1>);
unsafe_pinned!(second: St2);
pub(super) fn new(stream1: St1, stream2: St2) -> Chain<St1, St2> {
Chain {
first: Some(stream1),
second: stream2,
}
}
}
impl<St1, St2: FusedStream> FusedStream for Chain<St1, St2> {
fn is_terminated(&self) -> bool {
self.first.is_none() && self.second.is_terminated()
}
}
impl<St1, St2> Stream for Chain<St1, St2>
where St1: Stream,
St2: Stream<Item=St1::Item>,
{
type Item = St1::Item;
fn poll_next(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<Self::Item>> {
if let Some(first) = self.as_mut().first().as_pin_mut() {
if let Some(item) = ready!(first.poll_next(cx)) {
return Poll::Ready(Some(item))
}
}
self.as_mut().first().set(None);
self.as_mut().second().poll_next(cx)
}
}