1use crate::stream_ext::Fuse;
2use crate::Stream;
3
4use core::pin::Pin;
5use core::task::{Context, Poll};
6use pin_project_lite::pin_project;
7
8pin_project! {
9 /// Stream returned by the [`chain`](super::StreamExt::chain) method.
10 pub struct Chain<T, U> {
11 #[pin]
12 a: Fuse<T>,
13 #[pin]
14 b: U,
15 }
16}
17
18impl<T, U> Chain<T, U> {
19 pub(super) fn new(a: T, b: U) -> Chain<T, U>
20 where
21 T: Stream,
22 U: Stream,
23 {
24 Chain { a: Fuse::new(a), b }
25 }
26}
27
28impl<T, U> Stream for Chain<T, U>
29where
30 T: Stream,
31 U: Stream<Item = T::Item>,
32{
33 type Item = T::Item;
34
35 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T::Item>> {
36 use Poll::Ready;
37
38 let me = self.project();
39
40 if let Some(v) = ready!(me.a.poll_next(cx)) {
41 return Ready(Some(v));
42 }
43
44 me.b.poll_next(cx)
45 }
46
47 fn size_hint(&self) -> (usize, Option<usize>) {
48 super::merge_size_hints(self.a.size_hint(), self.b.size_hint())
49 }
50}
51