移动语义

An assignment will transfer ownership between variables:

fn main() {
    let s1: String = String::from("Hello!");
    let s2: String = s1;
    println!("s2: {s2}");
    // println!("s1: {s1}");
}

• 将 s1 赋值给 s2，即转移了所有权。
• When s1 goes out of scope, nothing happens: it does not own anything.
• 当 s2 离开作用域时，字符串数据被释放。
• 变量绑定在任一时刻有且“只有”一个值。