Now we can create a server instance and bind to this address:

let builder = Server::bind(&addr);

The preceding line creates a hyper::server::Server instance with a bind constructor that actually returns Builder, not a Server instance. The Server struct implements the Future trait. It has similar role to Result, but describes a value that isn't available immediately. You'll learn more about Future and other traits of the futures crate in Chapter 5, Understanding Asynchronous Operations with the Futures Crate.