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use core::pin::Pin;
use futures_core::future::{FusedFuture, Future, TryFuture};
use futures_core::task::{Context, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
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>);
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, E> FusedFuture for MapErr<Fut, F>
where Fut: TryFuture,
F: FnOnce(Fut::Error) -> E,
{
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>,
cx: &mut Context<'_>,
) -> Poll<Self::Output> {
self.as_mut()
.future()
.try_poll(cx)
.map(|result| {
let f = self.as_mut().f().take()
.expect("MapErr must not be polled after it returned `Poll::Ready`");
result.map_err(f)
})
}
}