分配后如何处理可变变量？

Question

从其他问题，我想出了如何构建复杂的JSON对象。要正确获取我的JSON对象，我需要检查是否已为此result_object分配了“密钥”。

由于对象现在是&mut，我无法将其用于其他操作，例如if条件。

我该如何处理这样的情况？

#[macro_use]
extern crate serde_json;

fn main() {
    let my_vec = ["foo", "bar", "baz", "foobar", "barfoo"];
    let mut curr_obj = json!(null);
    {
        let mut obj_ref = &mut curr_obj;
        for i in 0..my_vec.len() {
            let name = my_vec[i];

            if curr_obj.is_null() {
                //do stuff
            }
            obj_ref = &mut { obj_ref }[name]; // note the curly braces
        }
    }
    println!("{:?}", curr_obj);
}

错误：

error[E0502]: cannot borrow `curr_obj` as immutable because it is also borrowed as mutable
  --> src/main.rs:12:16
   |
8  |         let mut obj_ref = &mut curr_obj;
   |                                -------- mutable borrow occurs here
...
12 |             if curr_obj.is_null() {
   |                ^^^^^^^^ immutable borrow occurs here
...
17 |     }
   |     - mutable borrow ends here