blob: 7137e5c69d1baf4e3ab36d00f67ea8cee0bf8382 [file] [log] [blame]
use super::chain::Chain;
use core::fmt;
use core::pin::Pin;
use futures_core::future::{FusedFuture, Future};
use futures_core::task::{LocalWaker, Poll};
use pin_utils::unsafe_pinned;
/// Future for the `flatten` combinator.
///
/// This combinator turns a `Future`-of-a-`Future` into a single `Future`.
///
/// This is created by the `Future::flatten` method.
#[must_use = "futures do nothing unless polled"]
pub struct Flatten<Fut>
where Fut: Future,
Fut::Output: Future,
{
state: Chain<Fut, Fut::Output, ()>,
}
impl<Fut> Flatten<Fut>
where Fut: Future,
Fut::Output: Future,
{
unsafe_pinned!(state: Chain<Fut, Fut::Output, ()>);
pub(super) fn new(future: Fut) -> Flatten<Fut> {
Flatten {
state: Chain::new(future, ()),
}
}
}
impl<Fut> fmt::Debug for Flatten<Fut>
where Fut: Future + fmt::Debug,
Fut::Output: Future + fmt::Debug,
{
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
fmt.debug_struct("Flatten")
.field("state", &self.state)
.finish()
}
}
impl<Fut> FusedFuture for Flatten<Fut>
where Fut: Future,
Fut::Output: Future,
{
fn is_terminated(&self) -> bool { self.state.is_terminated() }
}
impl<Fut> Future for Flatten<Fut>
where Fut: Future,
Fut::Output: Future,
{
type Output = <Fut::Output as Future>::Output;
fn poll(self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Self::Output> {
self.state().poll(lw, |a, ()| a)
}
}