You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: select.rs
    path of file: ./repos/embassy/embassy-futures/src
    
    the code of the file until where you have to start completion: //! Wait for the first of several futures to complete.

use core::future::Future;
use core::pin::Pin;
use core::task::{Context, Poll};

/// Result for [`select`].
#[derive(Debug, Clone)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub enum Either<A, B> {
    /// First future finished first.
    First(A),
    /// Second future finished first.
    Second(B),
}

/// 
    
    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = unsafe { self.get_unchecked_mut() };
        let a = unsafe { Pin::new_unchecked(&mut this.a) };
        let b = unsafe { Pin::new_unchecked(&mut this.b) };
        let c = unsafe { Pin::new_unchecked(&mut this.c) };
        let d = unsafe { Pin::new_unchecked(&mut this.d) };
        if let Poll::Ready(x) = a.poll(cx) {
            return Poll::Ready(Either4::First(x));
        }
        if let Poll::Ready(x) = b.poll(cx) {
            return Poll::Ready(Either4::Second(x));
        }
        if let Poll::Ready(x) = c.poll(cx) {
            return Poll::Ready(Either4::Third(x));
        }
        if let Poll::Ready(x) = d.poll(cx) {
            return Poll::Ready(Either4::Fourth(x));
        }
        Poll::Pending
    }