once_cell

A macroless alternative to lazy_static. If you like this, you might also like lazycell.

fn hashmap() -> &'static HashMap<u32, &'static str> {
    static INSTANCE: OnceCell<HashMap<u32, &'static str>> = OnceCell::INIT;
    INSTANCE.get_or_init(|| {
        let mut m = HashMap::new();
        m.insert(0, "foo");
        m.insert(1, "bar");
        m.insert(2, "baz");
        m
    })
}

If you want slightly sweeter syntax, we have macros too!

static HASHMAP: Lazy<HashMap<u32, &'static str>> = sync_lazy! {
    let mut m = HashMap::new();
    m.insert(0, "foo");
    m.insert(1, "bar");
    m.insert(2, "baz");
    m
};

Note that this crate requires at least rustc 1.29 and the beta Cargo feature to enable full API. Without it, sync::Lazy works only in static contexts and requires explicit .deref_static call for dereference.