orbtk example with trait

summarize.rs

// Based on https://github.com/redox-os/orbtk/blob/a9653954fed7275328bc8e893c3465506154571e/examples/clear.rs
// Modified to add a trait member called "summary" which is either implemented as a Book or a NewsArticle
// The summarize button would call the trait function "summarize" (be it from Book or NewsArticle).
// I couldn't get this to work yet, with the troubling sections marked with FIXME

use orbtk::prelude::*;

//---------------------------------------
// https://doc.rust-lang.org/1.30.0/book/second-edition/ch10-02-traits.html
pub trait Summary {
  fn summarize(&self) -> String;
}
pub struct NewsArticle {
  pub headline: String,
}
impl Summary for NewsArticle {  
  fn summarize(&self) -> String {
    format!("news article: {}", self.headline)
  }
}
pub struct Book {
  pub title: String,
}
impl Summary for Book {
  fn summarize(&self) -> String {
    format!("book: {}", self.title)
  }
}

//---------------------------------------


#[derive(Default, AsAny)]
pub struct MainViewState {
    summarize: bool,
}

impl MainViewState {
    // Sets an action the state
    fn summarize(&mut self) {
        self.summarize = true;
    }
}

impl State for MainViewState {
    fn update(&mut self, _: &mut Registry, ctx: &mut Context<'_>) {
        if self.summarize {
            // Clears the text property of MainView and because
            // of the sharing also the text of the TextBox.
            let summary = *ctx.widget().get::<Summary>("summary"); // trait not allowed  <<<<<<<<< FIXME
            ctx.widget().set("text", String16::from(summary.summarize()));
            self.summarize = false;
        }
    }
}

widget!(MainView<MainViewState> {
    text: String16,
    summary: Summary // doesn't have a size known at compile-time <<<<<<<<< FIXME
    //summary: dyn Summary // no rules expected this token in macro call
    //summary: &Summary,
    //summary: PropertySource<Summary>,
});

impl Template for MainView {
    fn template(self, id: Entity, ctx: &mut BuildContext) -> Self {
        self.name("MainView").child(
            Stack::create()
                .orientation("horizontal")
                // By injecting the id of the parent the text property
                // is shared between the MainView and the TextBox. This
                // means both references the same String16 object.
                .child(TextBox::create().height(32.0).text(id).build(ctx))
                .child(
                    Button::create()
                        .margin((8.0, 0.0, 0.0, 0.0))
                        // mouse click event handler
                        .on_click(move |states, _| {
                            // Calls clear of the state of MainView
                            states.get_mut::<MainViewState>(id).summarize();
                            true
                        })
                        .text("Summarize")
                        .build(ctx),
                )
                .build(ctx),
        )
    }
}

fn main() {
    Application::new()
        .window(|ctx| {
            let main_view = MainView::create();
          
            // Allow to either pass a Book or a NewsArticle
            main_view.summary = Some(PropertySource::Value(Book { title: "The Jungle Book" }));
            // main_view.summary = Some(PropertySource::Value(NewsArticle { headline: "Dumbo the great!" }));

            Window::create()
                .title("OrbTk - minimal example")
                .position((100.0, 100.0))
                .size(420.0, 730.0)
                .child(main_view.margin(4.0).build(ctx))
                .build(ctx)
        })
        .run();
}