中文
devexamples

Once Lock Lazy Initialization

Initialize shared configuration exactly once on first use with std OnceLock, avoiding locks after setup.

RustConfig Management

Code

snippet
use std::sync::OnceLock;

static CONFIG: OnceLock<String> = OnceLock::new();

fn load_config() -> String {
    std::env::var("APP_CONFIG").unwrap_or_else(|_| "default".to_string())
}

pub fn config() -> &'static str {
    CONFIG.get_or_init(load_config)
}

pub fn try_override(value: &str) -> Result<(), &'static str> {
    CONFIG.set(value.to_string()).map_err(|_| "config already initialized")
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn init_is_idempotent() {
        let first = config();
        let second = config();
        assert_eq!(first, second);
    }
}

Related Examples