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//! Definition of the `SelectAll`, finding the first future in a list that
//! finishes.
use std::mem;
use std::prelude::v1::*;
use {Future, IntoFuture, Poll, Async};
/// Future for the `select_all` combinator, waiting for one of any of a list of
/// futures to complete.
/// This is created by the `select_all` function.
#[must_use = "futures do nothing unless polled"]
pub struct SelectAll<A> where A: Future {
inner: Vec<A>,
pub type SelectAllNext<A> = A;
/// Creates a new future which will select over a list of futures.
/// The returned future will wait for any future within `iter` to be ready. Upon
/// completion or failure the item resolved will be returned, along with the
/// index of the future that was ready and the list of all the remaining
/// futures.
/// # Panics
/// This function will panic if the iterator specified contains no items.
pub fn select_all<I>(iter: I) -> SelectAll<<I::Item as IntoFuture>::Future>
where I: IntoIterator,
I::Item: IntoFuture,
let ret = SelectAll {
inner: iter.into_iter()
.map(|a| a.into_future())
assert!(ret.inner.len() > 0);
impl<A> Future for SelectAll<A>
where A: Future,
type Item = (A::Item, usize, Vec<A>);
type Error = (A::Error, usize, Vec<A>);
fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
let item = self.inner.iter_mut().enumerate().filter_map(|(i, f)| {
match f.poll() {
Ok(Async::NotReady) => None,
Ok(Async::Ready(e)) => Some((i, Ok(e))),
Err(e) => Some((i, Err(e))),
match item {
Some((idx, res)) => {
let rest = mem::replace(&mut self.inner, Vec::new());
match res {
Ok(e) => Ok(Async::Ready((e, idx, rest))),
Err(e) => Err((e, idx, rest)),
None => Ok(Async::NotReady),