Rust lazy_static!


Use the lazy_static crate to create global immutable variables which are initialized at runtime. We use HashMap as a demonstration.

In Cargo.toml:

lazy_static = "0.1.*"


extern crate lazy_static;

lazy_static! {
    static ref HASHMAP: HashMap<u32, &'static str> = {
        let mut m = HashMap::new();
        m.insert(0, "hello");
        m.insert(1, ",");
        m.insert(2, " ");
        m.insert(3, "world");
    static ref COUNT: usize = HASHMAP.len();

fn main() {
    // We dereference COUNT because it's type is &usize
    println!("The map has {} entries.", *COUNT);

    // Here we don't dereference with * because of Deref coercions
    println!("The entry for `0` is \"{}\".", HASHMAP.get(&0).unwrap());