#[must_use = "this `Poll` may be a `Pending` variant, which should be handled"]
#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub enum Poll<T> {
    Ready(T),
    Pending,
}

impl<T> Poll<T> {
    pub fn map<U, F>(self, f: F) -> Poll<U>
    where
        F: FnOnce(T) -> U,
    {
        match self {
            Poll::Ready(t) => Poll::Ready(f(t)),
            Poll::Pending => Poll::Pending,
        }
    }

    #[inline]
    pub fn is_ready(&self) -> bool {
        match *self {
            Poll::Ready(_) => true,
            _ => false,
        }
    }

    #[inline]
    pub fn is_pending(&self) -> bool {
        !self.is_ready()
    }
}

impl<T, E> Poll<Result<T, E>> {
    pub fn map_ok<U, F>(self, f: F) -> Poll<Result<U, E>>
    where
        F: FnOnce(T) -> U,
    {
        match self {
            Poll::Ready(Ok(t)) => Poll::Ready(Ok(f(t))),
            Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
            Poll::Pending => Poll::Pending,
        }
    }

    pub fn map_err<U, F>(self, f: F) -> Poll<Result<T, U>>
    where
        F: FnOnce(E) -> U,
    {
        match self {
            Poll::Ready(Ok(t)) => Poll::Ready(Ok(t)),
            Poll::Ready(Err(e)) => Poll::Ready(Err(f(e))),
            Poll::Pending => Poll::Pending,
        }
    }
}

impl<T> From<T> for Poll<T> {
    fn from(t: T) -> Poll<T> {
        Poll::Ready(t)
    }
}