相关疑难解决方法(0)

这是我想要做的:

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}
}

引发以下错误:

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>`

我真的不明白这意味着什么,因为我做了HashMap可变的.当我尝试更新a中的元素时vector,我得到了预期的结果:

error[E0594]: cannot assign to data in …