在两个哈希映射之间交换值

我有两个HashMaps,并希望在某些条件下交换它们之间的值.如果第二个密钥不存在HashMap,则应插入密钥.我不想克隆该值,因为这太贵了.

(简化的)关键代码不起作用如下:

match hm1.get_mut(&1) {
    Some(ref mut x) => match hm.entry(1) {
        Entry::Occupied(mut y) => if y.get().replace {
            mem::swap(x, &mut y.get_mut());
        },
        Entry::Vacant(y) => {
            y.insert(mem::replace(x, dummy));
        }
    },
    NOne=> {}
}

(在Rust Playground)

我收到错误:

error[E0597]: `y` does not live long enough
  --> src/main.rs:28:9
   |
23 |                 mem::swap(x, &mut y.get_mut());
   |                                   - borrow occurs here
...
28 |         },
   |         ^ `y` dropped here while still borrowed
29 |         NOne=> {}
30 |     }
   |     - borrowed value needs to live until here

&mut y.get_mut()

&mut &mut ExpensiveStruct

match hm1.get_mut(&1) {
    Some(ref mut x) =>

match hm1.get_mut(&1) {
    Some(x) => match hm.entry(1) {
        Entry::Occupied(mut y) => if y.get().replace {
            mem::swap(x, y.get_mut());