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    //! Definition of the Empty combinator, a future that's never ready.

    use core::marker;

    use {Future, Poll, Async};

    /// A future which is never resolved.
    ///
    /// This future can be created with the `empty` function.
    #[derive(Debug)]
    #[must_use = "futures do nothing unless polled"]
    pub struct Empty<T, E> {
        _data: marker::PhantomData<(T, E)>,
    }

    /// Creates a future which never resolves, representing a computation that never
    /// finishes.
    ///
    /// The returned future will forever return `Async::NotReady`.
    pub fn empty<T, E>() -> Empty<T, E> {
        Empty { _data: marker::PhantomData }
    }

    impl<T, E> Future for Empty<T, E> {
        type Item = T;
        type Error = E;

        fn poll(&mut self) -> Poll<T, E> {
            Ok(Async::NotReady)
        }
    }

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