Use of OnceLock instead of lazy_static in regex validator.

[your-diary]

regex validator takes a static Regex instance.
This used to be created via an external crate such as lazy_static.
However, in modern Rust, recently added std::sync::OnceLock is often used for that purpose (though lazy_static is still widely used.)

Is it possible to pass OnceLock to regex validator?

lazy_static

use lazy_static::lazy_static;
use regex::Regex;
use serde::{Deserialize, Serialize};
use validator::Validate;

lazy_static! {
    static ref REGEX: Regex = Regex::new(r#"e$"#).unwrap();
}

#[derive(Debug, Deserialize, Serialize, Validate)]
struct S {
    #[validate(regex = "REGEX")]
    name: String,
}

impl S {
    fn new(json_string: &str) -> Self {
        serde_json::from_str(json_string).unwrap()
    }
}

fn main() {
    let json_string = r#"
        {
            "name": "Mike"
        }
    "#;
    let s = S::new(json_string);
    assert!(s.validate().is_ok());
}

OnceLock (doesn't compile)

use std::sync::OnceLock;

use regex::Regex;
use serde::{Deserialize, Serialize};
use validator::Validate;

static REGEX: OnceLock<Regex> = OnceLock::new();

#[derive(Debug, Deserialize, Serialize, Validate)]
struct S {
    #[validate(regex = "REGEX")]
    name: String,
}

impl S {
    fn new(json_string: &str) -> Self {
        serde_json::from_str(json_string).unwrap()
    }
}

fn main() {
    REGEX.set(Regex::new(r#"e$"#).unwrap());

    let json_string = r#"
        {
            "name": "Mike"
        }
    "#;
    let s = S::new(json_string);
    assert!(s.validate().is_ok());
}

[Keats]

Let's make sure this works in #262