Still watching, but I was confused at first because I thought “Counter example in druid” meant it was a counterexample to show why a new approach was needed (and I thought that was funny, because it looked very reasonable), but it was actually an example of a counter. :-D

Playing around with this declarative ui thing using v9 ideas/the One Name Rule:

let mut window = Window::new("Hi");

// Window holds the app's state.
// You want as many discrete objects as possible.
struct Count {
    n: i32,
}
window.register(Count { n: 0 });

let button = window.add::<Button>();
let label: Id<Label> = window.add::<Label>();
// Same as (PhantomData<W>, u64)

window.on(event::Press(button), |count: &mut Count| {
    count.n += 1
    // The mutable reference means that the Count object may have changed.
    // So any dependencies will need to be updated.
});
window.set0(label, |widget: &mut Label, count: &Count| {
    // This closure uses &Count, so we infer `label` to be a dependency.
    widget.text = format!("Count: {}", count.n);
});
window.set1(label, |count: &Count| -> String {
    // We can do this better.
    // &mut Label is very broad, so instead of modifying the entire object,
    // we could modify just one particular sub-object.
    // `Label` implements a trait that allows it to handle `String` objects being thrown at it.
    format!("Count: {}", count.n)
});
window.set2(label, |text: &mut String, count: &Count| {
    // We could modify the sub-object by reference; not allocating is nice.
    text.clear();
    write!(text, "Count: {}", count.n);
});
// It's also acceptable to have a 0-argument closure.
window.set3(button, || String::from("Increment"));
// It doesn't need to be a closure, and it doesn't need to be a String.
// (These sorts of niceties would be specially provided by Widgets.)
window.set4(button, "Increment");
// (These set functions could all be overloaded to just `set`, but maybe not both set0 and set2.)

window.run();