问如何更新可变HashMap中的值？

EN

use std::collections::HashMap;

fn main() {
    let mut my_map = HashMap::new();
    my_map.insert("a", 1);
    my_map.insert("b", 3);

    my_map["a"] += 10;
    // I expect my_map becomes {"b": 3, "a": 11}
}

error[E0594]: cannot assign to immutable indexed content
 --> src/main.rs:8:5
  |
8 |     my_map["a"] += 10;
  |     ^^^^^^^^^^^^^^^^^ cannot borrow as mutable
  |
  = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<&str, i32>`

error[E0594]: cannot assign to data in a `&` reference
 --> src/main.rs:8:5
  |
8 |     my_map["a"] += 10;
  |     ^^^^^^^^^^^^^^^^^ cannot assign

let mut my_vec = vec![1, 2, 3];

my_vec[0] += 10;
println! {"{:?}", my_vec};
// [11, 2, 3]