1use core::pin::Pin;
2use futures_core::ready;
3use futures_core::stream::{FusedStream, Stream};
4use futures_core::task::{Context, Poll};
5#[cfg(feature = "sink")]
6use futures_sink::Sink;
7use pin_project_lite::pin_project;
8
9pin_project! {
10 /// Stream for the [`fuse`](super::StreamExt::fuse) method.
11 #[derive(Debug)]
12 #[must_use = "streams do nothing unless polled"]
13 pub struct Fuse<St> {
14 #[pin]
15 stream: St,
16 done: bool,
17 }
18}
19
20impl<St> Fuse<St> {
21 pub(super) fn new(stream: St) -> Self {
22 Self { stream, done: false }
23 }
24
25 /// Returns whether the underlying stream has finished or not.
26 ///
27 /// If this method returns `true`, then all future calls to poll are
28 /// guaranteed to return `None`. If this returns `false`, then the
29 /// underlying stream is still in use.
30 pub fn is_done(&self) -> bool {
31 self.done
32 }
33
34 delegate_access_inner!(stream, St, ());
35}
36
37impl<S: Stream> FusedStream for Fuse<S> {
38 fn is_terminated(&self) -> bool {
39 self.done
40 }
41}
42
43impl<S: Stream> Stream for Fuse<S> {
44 type Item = S::Item;
45
46 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
47 let this = self.project();
48
49 if *this.done {
50 return Poll::Ready(None);
51 }
52
53 let item = ready!(this.stream.poll_next(cx));
54 if item.is_none() {
55 *this.done = true;
56 }
57 Poll::Ready(item)
58 }
59
60 fn size_hint(&self) -> (usize, Option<usize>) {
61 if self.done {
62 (0, Some(0))
63 } else {
64 self.stream.size_hint()
65 }
66 }
67}
68
69// Forwarding impl of Sink from the underlying stream
70#[cfg(feature = "sink")]
71impl<S: Stream + Sink<Item>, Item> Sink<Item> for Fuse<S> {
72 type Error = S::Error;
73
74 delegate_sink!(stream, Item);
75}
76