部分的ムーブ

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.

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

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

    // `name` は person からムーブしたが、 `age` は参照されています。
    let Person { name, ref age } = person;

    println!("The person's age is {}", age);

    println!("The person's name is {}", name);

    // エラー！部分的ムーブした値の借用：`person` では部分的ムーブが発生しています。
    //println!("The person struct is {:?}", person);

    // `person` は使用できませんが、
    // `person.age` はムーブしていないので使用できます。
    println!("The person's age from person struct is {}", person.age);
}

(In this example, we store the age variable on the heap to illustrate the partial move: deleting ref in the above code would give an error as the ownership of person.age would be moved to the variable age. If Person.age were stored on the stack, ref would not be required as the definition of age would copy the data from person.age without moving it.)

参照

デストラクト