以下是我想做的:
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}
}
但这引发了一个错误:
Rust 2015
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>`
Rust 2018
error[E0594]: cannot assign to data in a `&` reference
--> src/main.rs:8:5
|
8 | my_map["a"] += 10;
| ^^^^^^^^^^^^^^^^^ cannot assign
我真的不明白这意味着什么，因为我让HashMap变了.当我try 更新vector中的一个元素时，我得到了预期的结果:
let mut my_vec = vec![1, 2, 3];
my_vec[0] += 10;
println! {"{:?}", my_vec};
// [11, 2, 3]
我得到的上述错误与HashMap有什么不同？有没有办法更新一个值？