use std::thread;
use std::thread::JoinHandle;

struct A {
    field: i32,
    th: Option<JoinHandle<()>>,
}

impl A {
    fn foo(&mut self) {
        self.th = Some(thread::spawn(|| {
            bar(&self.field);
        }));
    }
}

impl Drop for A {
    fn drop(&mut self) {
        self.th.unwrap().join();
    }
}

fn bar(_: &i32) {}