lateinit

Disclaimer: this crate breaks Rust's safety guarantees. You should probably be using spin::Once, std::sync::Once, or lazy_static instead. If you're sure you want zero-cost late initialization at the cost of safety, read on.

[dependencies]
lateinit = "0.1"

The LateInit type provides an unsafe interface for initializing static variables at runtime. Design goals for this crate are to provide checked, one-time initialization and unchecked, zero-cost access thereafter.

static SOMETHING: LateInit<String> = LateInit::new();

fn main() {
    let environment_value = std::env::var("ENV_VALUE").unwrap();
    unsafe { SOMETHING.init(environment_value); }
    
    println!("{}", SOMETHING);
}

This crate should be used sparingly and carefully—it breaks Rust's safety guarantees. It's on you to ensure that you initialize your LateInits before accessing. Bad things™ will happen otherwise. It's heavily suggested that you initialize only in a clearly demarcated region of setup code.

Features

#[no_std] is supported.

By default, init asserts that it hasn't been called before, and there are debug_asserts in the Deref and AsRef implementations to catch potential errors while testing. If for some reason you want to turn these safety measures off, you can enable the unchecked feature flag and they will be compiled out.