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use core::marker;
use {Future, Poll};
/// A future representing a finished but erroneous computation.
///
/// Created by the `failed` function.
#[must_use = "futures do nothing unless polled"]
pub struct Failed<T, E> {
_t: marker::PhantomData<T>,
e: Option<E>,
}
/// Creates a "leaf future" from an immediate value of a failed computation.
///
/// The returned future is similar to `done` where it will immediately run a
/// scheduled callback with the provided value.
///
/// # Examples
///
/// ```
/// use futures::*;
///
/// let future_of_err_1 = failed::<u32, u32>(1);
/// ```
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"))
}
}