部分移动

Within the destructuring of a single variable, both by-move and by-reference pattern bindings can be used at the same time. Doing this will result in a partial move of the variable, which means that parts of the variable will be moved while other parts stay. In such a case, the parent variable cannot be used afterwards as a whole, however the parts that are only referenced (and not moved) can still be used. Note that types that implement the Drop trait cannot be partially moved from, because its drop method would use it afterwards as a whole.

fn main() {
    #[derive(Debug)]
    struct Person {
        name: String,
        age: Box<u8>,
    }

    // Error! cannot move out of a type which implements the `Drop` trait
    //impl Drop for Person {
    //    fn drop(&mut self) {
    //        println!("Dropping the person struct {:?}", self)
    //    }
    //}
    // TODO ^ Try uncommenting these lines

    let person = Person {
        name: String::from("Alice"),
        age: Box::new(20),
    };

    // `name` 从 person 中被移出，但 `age` 只是被引用
    let Person { name, ref age } = person;

    println!("此人的年龄是 {}", age);

    println!("此人的姓名是 {}", name);

    // 错误！借用部分移动的值：`person` 发生部分移动
    //println!("person 结构体是 {:?}", person);

    // `person` 不能使用，但 `person.age` 可以使用，因为它没有被移动
    println!("从 person 结构体中获取的年龄是 {}", person.age);
}

（在这个例子中，我们将 age 变量存储在堆上以说明部分移动：删除上面代码中的 ref 会导致错误，因为 person.age 的所有权会被移动到变量 age。如果 Person.age 存储在栈上，就不需要 ref，因为 age 的定义会从 person.age 复制数据而不是移动它。）

另请参阅：

解构