Code shared from the Rust Playground

playground.rs

use std::sync::Mutex;


#[macro_use]
extern crate lazy_static;

#[derive(Debug)]
struct MyDB {}

lazy_static! {
    static ref DB: Mutex<Option<MyDB>> = Mutex::new(None);    
}


fn get_db() -> Option<&'static MyDB> {
    let mtx = DB.lock().unwrap();
    let db = mtx.as_ref();
    match db {
        None => {
            let d = MyDB {};
            DB.lock().unwrap().replace(d);
            None
        },
        Some(ref d) => {
            Some(d)
        }
    }
}

fn main() {
    let db = get_db();
    println!("{:?}", db);
}