use std::rc::Rc; // reference-counted, non atomic
use std::sync::Arc; // reference-counted, atomic

fn main() {
    // this will not compile:
    let rc = Rc::new("not thread safe");
    std::thread::spawn(move || {
        println!("I have an rc with: {}", rc);
    });

    // this compiles fine:
    let arc = Arc::new("thread safe");
    std::thread::spawn(move || {
        println!("I have an arc with: {}", arc);
    });

    // this will also not compile:
    let mut v = Vec::new();
    std::thread::spawn(|| {
        v.push(42);
    });
    let _ = v.pop();
}