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    //! Definition of the `Result` (immediately finished) combinator

    use core::result;

    use {Future, Poll, Async};

    /// A future representing a value that is immediately ready.
    ///
    /// Created by the `result` function.
    #[derive(Debug, Clone)]
    #[must_use = "futures do nothing unless polled"]
    // TODO: rename this to `Result` on the next major version
    pub struct FutureResult<T, E> {
        inner: Option<result::Result<T, E>>,
    }

    /// Creates a new "leaf future" which will resolve with the given result.
    ///
    /// The returned future represents a computation which is finished immediately.
    /// This can be useful with the `finished` and `failed` base future types to
    /// convert an immediate value to a future to interoperate elsewhere.
    ///
    /// # Examples
    ///
    /// ```
    /// use futures::future::*;
    ///
    /// let future_of_1 = result::<u32, u32>(Ok(1));
    /// let future_of_err_2 = result::<u32, u32>(Err(2));
    /// ```
    pub fn result<T, E>(r: result::Result<T, E>) -> FutureResult<T, E> {
        FutureResult { inner: Some(r) }
    }

    /// Creates a "leaf future" from an immediate value of a finished and
    /// successful computation.
    ///
    /// The returned future is similar to `result` where it will immediately run a
    /// scheduled callback with the provided value.
    ///
    /// # Examples
    ///
    /// ```
    /// use futures::future::*;
    ///
    /// let future_of_1 = ok::<u32, u32>(1);
    /// ```
    pub fn ok<T, E>(t: T) -> FutureResult<T, E> {
        result(Ok(t))
    }

    /// Creates a "leaf future" from an immediate value of a failed computation.
    ///
    /// The returned future is similar to `result` where it will immediately run a
    /// scheduled callback with the provided value.
    ///
    /// # Examples
    ///
    /// ```
    /// use futures::future::*;
    ///
    /// let future_of_err_1 = err::<u32, u32>(1);
    /// ```
    pub fn err<T, E>(e: E) -> FutureResult<T, E> {
        result(Err(e))
    }

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

        fn poll(&mut self) -> Poll<T, E> {
            self.inner.take().expect("cannot poll Result twice").map(Async::Ready)
        }
    }

    impl<T, E> From<Result<T, E>> for FutureResult<T, E> {
        fn from(r: Result<T, E>) -> Self {
            result(r)
        }
    }

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