A Rust data structure that can store closures and invoke them. A poor mans version of `event` from C#.

event.rs

struct Event<'a> {
    handlers: Vec<Box<FnMut() + 'a>>,
}

impl<'a> Event<'a> {
    fn new() -> Self {
        Self {
            handlers: Vec::new(),
        }
    }
    
    fn invoke(&mut self) {
        for h in self.handlers.iter_mut() {
            h();
        }
    }
    
    fn add_handler<H: FnMut() + 'a>(&mut self, handler: H) {
        self.handlers.push(Box::new(handler));
    }
}

fn main() {
    let mut main_event_fired = false;

    let mut on_click_event = Event::new();
    on_click_event.add_handler(|| {
        if !main_event_fired {
            println!("Hello world!");
            main_event_fired = true;
        }
    });
    on_click_event.add_handler(|| println!("Kewl!"));
    on_click_event.invoke();
    on_click_event.invoke();
}