Global unmodifiable variables with OnceLock

main.rs

use std::sync::OnceLock;

static ADDRESSES: OnceLock<Vec<&str>> = OnceLock::new(); 

fn main() {
  assert!(ADDRESSES.get().is_none());

  let first_attempt = ADDRESSES.set(Vec::from([
    "http://validaddress.com",
    "http://mainmirror.com",
    "http://128.0.0.1:1337"
  ]));
  assert!(first_attempt.is_ok());

  check_addresses();

  // the initial value can't be overriden
  let second_attempt = ADDRESSES.set(Vec::new());
  assert!(second_attempt.is_err_and(|v| v.is_empty()))	// is_err_and is also a new addition of Rust 1.70

}

fn check_addresses() {
  // we have global access
  assert!(ADDRESSES.get().is_some());
  assert_eq!("http://validaddress.com", ADDRESSES.get().unwrap()[0]);
  println!("The address list is readable and correct: {:?}", ADDRESSES.get().unwrap())
}