extern crate futures; // 0.1.21

use futures::Future;
use futures::Stream;
use futures::Poll;
use futures::sync::mpsc::{unbounded, UnboundedSender, UnboundedReceiver};


struct A {
    tx: UnboundedSender<i32>,
}

struct B {
    rx: UnboundedReceiver<i32>,
}

impl Future for B {
    type Item = i32;
    type Error = ();

    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
        self.rx.poll().map(|a| a.map(|o| o.unwrap()))
    }
}

fn main() {
    let (tx, rx) = unbounded();
    let a = A { tx };
    let mut b = B { rx };

    b.poll();
}