Wouldn't it be better if the methods in the ApplicationHandler trait could return a Result?

[jmjoy]

Right now, none of the methods in ApplicationHandler return any value, so when calling other methods that return a Result within an implementation, I have no choice but to use unwrap.

It would be great if we could add an associated Error type to ApplicationHandler.

[kchibisov]

You can have other choice, ignore. since some of them(pretty much all) are not mandatory for application to run. Unless you're talking about other methods, in that case you can just mark event loop for exit, and bubble up the error via other means(e.g. Mutex).