Trying to create random number to const

Question

I'm trying to create a random number to const value using const_random and get the same value

I have the following code:

use const_random::const_random;


pub mod random_id{
    const NUMBER: u64 = const_random!(u64)
     
    pub fn get_number() - > u64 {
        return NUMBER;
    }
}

I got always the same number, how can I fix it?

Answer 1

Is this the kind of thing you're looking for?

use std::sync::OnceLock;

use rand; // 0.8.5

fn the_random_value() -> u64 {
    // A `static` value is shared and reused whenever you call the
    // function, and this `OnceLock::new()` will only be called once,
    // when the program starts.
    static RANDOM: OnceLock<u64> = OnceLock::new();

    // `OnceLock::get_or_init` is designed to be called only once,
    // when you reach this line for the first time.
    *RANDOM.get_or_init(rand::random)
}

fn main() {
    // This will print several times the same value,
    // but a different value upon each startup.
    println!("RANDOM: {}", the_random_value());
    println!("RANDOM: {}", the_random_value());
    println!("RANDOM: {}", the_random_value());
    println!("RANDOM: {}", the_random_value());
    println!("RANDOM: {}", the_random_value());
}

---

(another version, which uses the now mostly deprecated lazy_static)

use lazy_static::lazy_static; // 1.4.0
use rand; // 0.8.5


lazy_static!{
    // On the first call, this produces a random value.
    // Subsequent calls will reuse the same value.
    // Value is refreshed upon each start of the program.
    static ref RANDOM : u64 = rand::random();
}

fn main() {
    // This will print several times the same value,
    // but a different value upon each startup.
    println!("RANDOM: {}", *RANDOM);
    println!("RANDOM: {}", *RANDOM);
    println!("RANDOM: {}", *RANDOM);
    println!("RANDOM: {}", *RANDOM);
    println!("RANDOM: {}", *RANDOM);
}