extern crate lazy_static; // 1.4.0

use std::sync::Arc;
use std::sync::Mutex;
use std::ops::DerefMut;
use std::collections::HashMap;
use lazy_static::lazy_static;

lazy_static! {
    static ref HASHMAP: Arc<Mutex<HashMap<u64, String>>> = {
        let mut m = HashMap::new();
        m.insert(0, "foo".to_string());
        m.insert(1, "bar".to_string());
        m.insert(2, "baz".to_string());
        Arc::new(Mutex::new(m))
    };
}

fn main() {
    // get
    {
        let lk = HASHMAP.lock().unwrap();
        println!("{:?}", lk.get(&0));
    }

    // Swap
    {
        let mut m = HashMap::new();
        m.insert(0, "foo_foo".to_string());
        m.insert(1, "bar_foo".to_string());
        m.insert(2, "baz_foo".to_string());

        let mut lk = HASHMAP.lock().unwrap();
        std::mem::swap(lk.deref_mut(), &mut m);
    }

    // get again.
    {
        let lk = HASHMAP.lock().unwrap();
        println!("{:?}", lk.get(&0));
    }

}