1use super::assert_future;
2use crate::future::FutureExt;
3use alloc::vec::Vec;
4use core::iter::FromIterator;
5use core::mem;
6use core::pin::Pin;
7use futures_core::future::Future;
8use futures_core::task::{Context, Poll};
9
10/// Future for the [`select_all`] function.
11#[derive(Debug)]
12#[must_use = "futures do nothing unless you `.await` or poll them"]
13pub struct SelectAll<Fut> {
14 inner: Vec<Fut>,
15}
16
17impl<Fut: Unpin> Unpin for SelectAll<Fut> {}
18
19/// Creates a new future which will select over a list of futures.
20///
21/// The returned future will wait for any future within `iter` to be ready. Upon
22/// completion the item resolved will be returned, along with the index of the
23/// future that was ready and the list of all the remaining futures.
24///
25/// There are no guarantees provided on the order of the list with the remaining
26/// futures. They might be swapped around, reversed, or completely random.
27///
28/// This function is only available when the `std` or `alloc` feature of this
29/// library is activated, and it is activated by default.
30///
31/// # Panics
32///
33/// This function will panic if the iterator specified contains no items.
34pub fn select_all<I>(iter: I) -> SelectAll<I::Item>
35where
36 I: IntoIterator,
37 I::Item: Future + Unpin,
38{
39 let ret: SelectAll = SelectAll { inner: iter.into_iter().collect() };
40 assert!(!ret.inner.is_empty());
41 assert_future::<(<I::Item as Future>::Output, usize, Vec<I::Item>), _>(ret)
42}
43
44impl<Fut> SelectAll<Fut> {
45 /// Consumes this combinator, returning the underlying futures.
46 pub fn into_inner(self) -> Vec<Fut> {
47 self.inner
48 }
49}
50
51impl<Fut: Future + Unpin> Future for SelectAll<Fut> {
52 type Output = (Fut::Output, usize, Vec<Fut>);
53
54 fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
55 let item: Option<(usize, ::Output)> = self.inner.iter_mut().enumerate().find_map(|(i: usize, f: &mut Fut)| match f.poll_unpin(cx) {
56 Poll::Pending => None,
57 Poll::Ready(e: ::Output) => Some((i, e)),
58 });
59 match item {
60 Some((idx: usize, res: ::Output)) => {
61 #[allow(clippy::let_underscore_future)]
62 let _ = self.inner.swap_remove(index:idx);
63 let rest: Vec = mem::take(&mut self.inner);
64 Poll::Ready((res, idx, rest))
65 }
66 None => Poll::Pending,
67 }
68 }
69}
70
71impl<Fut: Future + Unpin> FromIterator<Fut> for SelectAll<Fut> {
72 fn from_iter<T: IntoIterator<Item = Fut>>(iter: T) -> Self {
73 select_all(iter)
74 }
75}
76