extern crate futures;
extern crate tokio;

mod hw {
    pub use futures::{Async, Future, Poll, try_ready};
    pub use std::fmt;

    pub struct HelloWorld;
    impl Future for HelloWorld {
        type Item = String;
        type Error = ();

        fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
            Ok(Async::Ready("helloworld".to_string()))
        }
    }

    pub struct Display<T>(pub T);
    impl<T> Future for Display<T>
    where
        T: Future,
        T::Item: fmt::Display,
    {
        type Item = ();
        type Error = T::Error;

        fn poll(&mut self) -> Poll<(), T::Error> {
            let value = try_ready!(self.0.poll());
            println!("{}", value);
            Ok(Async::Ready(()))
        }
    }
}

use hw::{Display, HelloWorld};

fn main() {
    let future = Display(HelloWorld);
    tokio::run(future);
}