futures_util/stream/stream/
fuse.rs

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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}
futures_util/stream/stream/fuse.rs

futures_util/stream/stream/
fuse.rs
