`

    fn do_work_and_then(func: fn(i32)) {
        thread::spawn(move || {
            // Figuring out the meaning of life...
            thread::sleep_ms(1000); // gee, this takes time to do...
            // ah, that's it!
            let result: i32 = 42;
            // let's call the `func` and tell it the good news...
            func(result)
        });
    }

`

you missed a snippet, a thread is spawned.

edit: formatting