blob: 058b49cf1fddc80b92c4584f614b701df5feb873 [file] [log] [blame]
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::future::{FusedFuture, Future, TryFuture};
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// Future for the [`map_err`](super::TryFutureExt::map_err) combinator.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct MapErr<Fut, F> {
future: Fut,
f: Option<F>,
}
impl<Fut, F> MapErr<Fut, F> {
unsafe_pinned!(future: Fut);
unsafe_unpinned!(f: Option<F>);
/// Creates a new MapErr.
pub(super) fn new(future: Fut, f: F) -> MapErr<Fut, F> {
MapErr { future, f: Some(f) }
}
}
impl<Fut: Unpin, F> Unpin for MapErr<Fut, F> {}
impl<Fut, F> FusedFuture for MapErr<Fut, F> {
fn is_terminated(&self) -> bool { self.f.is_none() }
}
impl<Fut, F, E> Future for MapErr<Fut, F>
where Fut: TryFuture,
F: FnOnce(Fut::Error) -> E,
{
type Output = Result<Fut::Ok, E>;
fn poll(
mut self: Pin<&mut Self>,
lw: &LocalWaker,
) -> Poll<Self::Output> {
match self.future().try_poll(lw) {
Poll::Pending => Poll::Pending,
Poll::Ready(result) => {
let f = self.f().take()
.expect("MapErr must not be polled after it returned `Poll::Ready`");
Poll::Ready(result.map_err(f))
}
}
}
}