Shared read-only variable with string value with Arc

---

• We can use Arc to create Reference Counting around the data.
• The clone on the Arc will only increment the reference counter, but does not copy the data.

examples/threads/shared-read-only-variable-string-with-arc/src/main.rs

use std::sync::Arc;
use std::time::Duration;

fn main() {
    let answer = Arc::new(String::from("Hello World!"));

    println!("Before:     {answer} {:p} {:?}", &answer, answer.as_ptr());
    let mut handles = vec![];
    for _ in 1..=3 {
        let answer = answer.clone();
        handles.push(std::thread::spawn(move || {
            println!(
                "{:?} {} {:p} {:?}",
                std::thread::current().id(),
                answer,
                &answer,
                answer.as_ptr()
            );
            std::thread::sleep(Duration::from_millis(10));
        }));
    }
    println!("Started:    {answer} {:p} {:?}", &answer, answer.as_ptr());
    for handle in handles {
        handle.join().unwrap();
    }
    println!("After:      {answer} {:p} {:?}", &answer, answer.as_ptr());
}

Before:     Hello World! 0x7fffeddb81b0 0x61db86afeb80
Started:    Hello World! 0x7fffeddb81b0 0x61db86afeb80
ThreadId(2) Hello World! 0x78f1c1bffa78 0x61db86afeb80
ThreadId(3) Hello World! 0x78f1c17ffa78 0x61db86afeb80
ThreadId(4) Hello World! 0x78f1c13ffa78 0x61db86afeb80
After:      Hello World! 0x7fffeddb81b0 0x61db86afeb80