Rust 中的 String 真的是引用类型吗？

Question

struct User {
    username: String,
    email: String,
    sign_in_count: u64,
    active: bool,
}

fn main() {
    let mut user = User {
        username: String::from("Paulx"),
        email: String::from("paulx@gmail.io"),
        sign_in_count: 0,
        active: true,
    };

    let name = user.username;
    user.username = String::from("Alix");

    println!("{}", name);
}

您将看到 是username从用户复制的变量name。变量name不是标量类型，为什么它可以复制呢？

Answer 1

我认为这里有一个误解。

你没有复制user.username，你把它移走了。

在您分配新的条目之前，user.username该条目user.username无效。

看这里：

struct User {
    username: String,
}

fn main() {
    let mut user = User {
        username: String::from("Paulx"),
    };

    let name = user.username;

    // Fails to compile!
    println!("{}", user.username);

    user.username = String::from("Alix");

    // Works again.
    println!("{}", user.username);

    println!("{}", name);
}

struct User {
    username: String,
}

fn main() {
    let mut user = User {
        username: String::from("Paulx"),
    };

    let name = user.username;

    // Fails to compile!
    println!("{}", user.username);

    user.username = String::from("Alix");

    // Works again.
    println!("{}", user.username);

    println!("{}", name);
}