map in a druid list widget

map_in_list_widget.rs

// Requires druid features = ["im"]
// And I *think* druid from git.
use im;
use druid::{self, lens, Data,
    widget::{Flex, List, Scroll, Widget, WidgetExt, Slider, ListIter}};

#[derive(Clone, Data, Debug)]
struct AppState {
    state: im::HashMap<String, f64>,
}

fn subwidget() -> impl Widget<f64> {
    Slider::new().with_range(0.0, 11.0).with_step(1.0)
}

impl ListIter<f64> for AppState
{
    fn for_each(&self, mut cb: impl FnMut(&f64, usize)) {
        for (i, (k, v)) in self.state.iter().enumerate() {
            let (_, v) = (k.to_owned(), v.to_owned());
            cb(&v, i);
        }
    }

    fn for_each_mut(&mut self, mut cb: impl FnMut(&mut f64, usize)) {
        let state = &mut self.state;
        for (i, (_k, v)) in state.iter_mut().enumerate() {
            let mut ret = v.clone();
            cb(&mut ret, i);

            if !v.same(&ret) {
                *v = ret;
            }
        }
    }

    fn data_len(&self) -> usize {
        self.state.len()
    }
}


fn top_level_widget() -> impl Widget<AppState> {
   let mut row = Flex::row();
   let list = List::new(move || subwidget());
   row.add_flex_child(
        Scroll::new(list).vertical().lens(lens::Identity),
        1.0
   );

   Flex::column().with_child(row)
}

fn main() {
    let mut state = im::HashMap::new();
    state.insert("foo".to_string(), 8.0);
    state.insert("bar".to_string(), 1.0);


    let window = druid::WindowDesc::new(top_level_widget())
        .title(druid::LocalizedString::new("hashmap appstate").with_placeholder("hashmap appstate"));
    let launcher = druid::AppLauncher::with_window(window);

    launcher.launch(AppState { state }).expect("launch failed");
    
    println!("Hello, world!");
}