use std::{collections::HashMap, hash::Hash};

fn get_default<'m, K, V>(map: &'m mut HashMap<K, V>, key: K) -> &'m mut V
where
    K: Eq + Hash,
    V: Default
{
    match map.get_mut(&key) {
        Some(value) => value,
        None => {
            map.insert(key, V::default());
            map.get_mut(&key).unwrap()
        }
    }
}

fn main() {
    println!("Hello, world!");
}