main.rs

use tokio::time::Duration;

async fn value<T>(x: T, duration: Duration) -> T {
    println!("Before sleeping in value");
    tokio::time::sleep(duration).await;
    println!("After sleeping in value");
    x
}

async fn identity<T>(x: &mut T) -> &mut T {
    println!("In identity");
    x
}

#[tokio::main]
async fn main() {
    let mut x = 0i32;
    println!("Before assignment");
    *identity(&mut x).await = value(42, Duration::from_secs(1)).await;
    println!("After assignment");
}