t_wの輪郭

insertを２回使う

hashmap.insert(String::from("Blue"), 10);
hashmap.insert(String::from("Blue"), 50);
println!("{:?}", hashmap)       // {"Blue": 50}

もしくはget_mutを使う

let key = String::from("Blue");

if let Some(v) = hashmap.get_mut(&key) {
    *v=100;
}

if let Some(v) = hashmap.get(&key) {
    println!("{}", v);      //100
}