Change a function from another task

fn_changer.rs

use tokio::time::{self, Duration};
use tokio::sync::Mutex;

use std::sync::Arc;

type FooFn = dyn Fn(u32) -> u32 + Send;

#[tokio::main]
async fn main() {
    let foo: Arc<Mutex<Option<Box<FooFn>>>> = Arc::new(Mutex::new(None));

    {
        let foo = foo.clone();

        tokio::spawn(async move {
            let mut interval = time::interval(Duration::from_secs(2));
            for i in 0u32.. {
                interval.tick().await;
                let mut foo = foo.lock().await;
                println!("changing foo");
                *foo = Some(Box::new(move |n| n * i));
            }
        });
    }


    let mut interval = time::interval(Duration::from_secs(1));

    for i in 0u32.. {
        interval.tick().await;
        println!("Calling foo");
        if let Some(ref foo) = *foo.lock().await {
            println!("foo({}) = {}", i, foo(i));
        } else {
            println!("no foo");
        }
    }
}