use std::sync::{Arc, Mutex};

#[derive(Debug)]
struct Foo(Arc<Mutex<usize>>);

impl Foo {
    fn mutate(&self) {
        let mut current = self.0.lock().unwrap();
        *current = 1;
    }
}

fn main() {
    let foo = Foo(Arc::new(Mutex::new(0)));
    println!("{:?}", foo);
    foo.mutate();
    println!("{:?}", foo);
}