add futures-based hello world

future-hello-world/src/main.rs

@@ -0,0 +1,40 @@
+#[macro_use]
+extern crate futures;
+extern crate tokio;
+
+use futures::{Future, Async, Poll};
+use std::fmt;
+
+struct HelloWorld;
+
+impl Future for HelloWorld {
+    type Item = String;
+    type Error = ();
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        Ok(Async::Ready("hello world".to_string()))
+    }
+}
+
+struct Display<T>(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(()))
+    }
+}
+
+fn main() {
+    let future = Display(HelloWorld);
+    tokio::run(future);
+}