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use core::marker;
use {Future, Poll};
#[must_use = "futures do nothing unless polled"]
pub struct Failed<T, E> {
_t: marker::PhantomData<T>,
e: Option<E>,
}
pub fn failed<T, E>(e: E) -> Failed<T, E> {
Failed { _t: marker::PhantomData, e: Some(e) }
}
impl<T, E> Future for Failed<T, E> {
type Item = T;
type Error = E;
fn poll(&mut self) -> Poll<T, E> {
Err(self.e.take().expect("cannot poll Failed twice"))
}
}