rune/runtime/
select.rs

1use core::future;
2use core::pin::Pin;
3use core::task::{Context, Poll};
4
5use futures_core::Stream;
6use futures_util::stream::FuturesUnordered;
7
8use crate::runtime::future::SelectFuture;
9use crate::runtime::{Future, Mut, Value, VmResult};
10
11/// A stored select.
12#[derive(Debug)]
13pub struct Select {
14    futures: FuturesUnordered<SelectFuture<usize, Mut<Future>>>,
15}
16
17impl Select {
18    /// Construct a new stored select.
19    pub(crate) fn new(futures: FuturesUnordered<SelectFuture<usize, Mut<Future>>>) -> Self {
20        Self { futures }
21    }
22}
23
24impl future::Future for Select {
25    type Output = VmResult<(usize, Value)>;
26
27    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
28        let poll = Pin::new(&mut self.futures).poll_next(cx);
29
30        let poll = match poll {
31            Poll::Ready(poll) => poll.expect("inner stream should never end"),
32            Poll::Pending => return Poll::Pending,
33        };
34
35        Poll::Ready(poll)
36    }
37}