1use gpui::{App, Application, Context, Entity, EventEmitter, prelude::*};
 2
 3struct Counter {
 4    count: usize,
 5}
 6
 7struct Change {
 8    increment: usize,
 9}
10
11impl EventEmitter<Change> for Counter {}
12
13fn main() {
14    Application::new().run(|cx: &mut App| {
15        let counter: Entity<Counter> = cx.new(|_cx| Counter { count: 0 });
16        let subscriber = cx.new(|cx: &mut Context<Counter>| {
17            cx.subscribe(&counter, |subscriber, _emitter, event, _cx| {
18                subscriber.count += event.increment * 2;
19            })
20            .detach();
21
22            Counter {
23                count: counter.read(cx).count * 2,
24            }
25        });
26
27        counter.update(cx, |counter, cx| {
28            counter.count += 2;
29            cx.notify();
30            cx.emit(Change { increment: 2 });
31        });
32
33        assert_eq!(subscriber.read(cx).count, 4);
34    });
35}