Better ways of initializing an ApplicationHandler

[Astralchroma]

Description

The ApplicationHandler API presents a problem for any application where a window is required before much can be done as you can't create a window until the first event, by which time you will have already created the struct to represent your application. This means you now have to use Option<T> to handle the possibility of no window at some point. The most sane way I have found to do this is to create my own separate application struct, which is stored as an Option<T> in the ApplicationHandler implementation and simply pass through all the events. This is somewhat messy, and not ideal.

As a solution, I would suggest changing how an event loop is started, the best way I can think of acomplishing this would be to introduce a new ApplicationHandler::init method, a rough overview of the idea is as follows:

struct Application {
	window: Window
}

impl ApplicationHandler<()> for Application {
	type PassedData = String;

	// The addition of PassedData is to make it convenient to pass anything created before the event loop, any API wouldn't necessarily need this, but it would be a useful thing to have.
	fn init(event_loop: &ActiveEventLoop, passed_data: PassedData) -> Self {
		println!("{passed_data}");
		Self {
			window: event_loop.create_window(Window::default_attributes()).unwrap(),
		}
	}
	
	// *All other functions would be same as they are currently*
}

fn main() {
	EventLoop::new()
		.unwrap()
		.run_app::<Application>(String::from("Hello World!"))
		.unwrap();
}

Relevant platforms

No response

[daxpedda]

Agreed, this could be improved.
I believe this is a duplicate of #2903.