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