How do I use a SelectView as a menu?

[sbowman]

Sorry if this is a dumb question, but I'm relatively new to Rust. (And, TBH, I think I'm finding that I'm not smart enough for this language...)

I'm trying to display an opening screen in my app that offers a few selections, then when you select one, removes the menu and replaces it with a new dialog. When you're done with that dialog, you come back to the menu, and select another item.

So, if I have a SelectView like this:

fn menu(siv: &mut Cursive) {
    let mut menu = SelectView::new()
        .h_align(HAlign::Left);

    menu.add_item("[A]bout", "about");
    menu.add_item("[Q]uit", "quit");

    menu.set_on_submit(|s, item| {
        match item {
            "about" => {
                s.pop_layer();
                about(s);
            }

            "quit" => s.quit(),
            _ => unreachable!()
        }
    });

    siv.add_layer(Dialog::around(menu));
}


fn about(siv: &mut Cursive) {
    let mut layout = LinearLayout::vertical();
    layout.add_child(TextView::new("Hello World!"));
    layout.add_child(Button::new("Ok", |s| {
        s.pop_layer();
        menu(s);
    }));
    siv.add_layer(layout);
}

Ideally when I select "About," it removes my menu and displays the about dialog. When I click ok on the about dialog, it would display my menu again. But this violates all sorts of lifetime/ownership rules in Rust.

I started this by trying to create a proper "Welcome" struct that would act as a state machine, tracking the state of what to display: menu, about, sign in, etc. But I wasn't able to modify my struct from within the event handler closure to change its state without violating all sorts of borrow checker rules.

Then I thought about a "WelcomeView," so from within the on_event closure I could get the WelcomeView by name from the Cursive reference passed into the closure and update its state, but it doesn't look like it's easy to create a custom view by just composing it of other views (looks like I need to write a lot of drawing, refresh, and resizing code?). But is this how I'm supposed to do this? Is there an example somewhere of a compositional view?

I'd really like to just be able to do something like:

menu.set_on_submit(|s, item| {
    match item {
        "about" => self.next(State::About),
        "quit" => s.quit(),
        _ => unreachable!()
    }
});

And have my self.next method refresh the display, replacing the menu with the about dialog...which is how I'd approach this in something like C++ or Go. But it seems like this won't work in Rust, since on_submit wants 'static?

Again, sorry if these are dumb questions. You're welcome to just tell me I don't get it, and I'm too new at this to be trying to use Cursive. At this point I'm ready to give up anyway. (For example, I pretty much find every article I read about Rust closures more confusing than the last.)

Thanks

[gyscos]

Hi!

I'm trying to display an opening screen in my app that offers a few selections, then when you select one, removes the menu and replaces it with a new dialog. When you're done with that dialog, you come back to the menu, and select another item.

The usual way to do that is not to remove the menu, but just to show something in front of the menu (possibly covering it entirely); and when you're done with it, remove that new thing, and the menu will still be there.

If you don't want the menu to be visible when not active, rather than removing it (and having to create it again later), you could switch to a different "screen". The Cursive root can store multiple screens, each with its own view stack.

You would have a menu screen with only the menu, and maybe another screen with the active view. You'd move from the menu screen to the active screen when selecting items, and when closing an active view, you'd come back to the menu screen.
It's very similar to what you're currently doing, only you don't need to remove and delete the menu. It means you only need to create the menu once (when initializing the app at the beginning), so you can pass more information to this menu() function.

If possible, it's best to avoid maintaining your own state machine for what should be displayed: it's exactly what cursive is doing internally.

But it seems like this won't work in Rust, since on_submit wants 'static?

This only means that the closure you're giving cannot borrow other data, but you can totally move stuff in there - including Rc or others if you need to share data with other components.

but it doesn't look like it's easy to create a custom view by just composing it of other views

You can either:

• Just make WelcomeView a type alias for the actual view you're using (maybe LinearLayout?), and just compose other view types.
• Make WelcomeView a thin wrapper around the inner view, and use the wrap_impl macro to easily implement ViewWrapper, effectively forwarding all view calls to the inner view. You can still override any methods if needed.

I pretty much find every article I read about Rust closures more confusing than the last

If you're used to C++, then closures in rust are very similar to C++ lambdas, only with less fine-grained control over ref/move for each parameter (if you need fine-grained control in rust you move every parameter, only some of the parameters are references).