Rust 寿命 - 书籍示例解决方案

Question

On Rust Book there's this lifetime example:

struct Foo<'a> {
    x: &'a i32,
}

fn main() {
    let x;                    // -+ x goes into scope
                              //  |
    {                         //  |
        let y = &5;           // ---+ y goes into scope
        let f = Foo { x: y }; // ---+ f goes into scope
        x = &f.x;             //  | | error here
    }                         // ---+ f and y go out of scope
                              //  |
    println!("{}", x);        //  |
}   

Simplifying this to:

fn main() {
    let x;
    {
        let y = 42;
        x = &y;
    }

    println!("The value of 'x' is {}.", x);
}

Is it possible to have it work without clone ?

Answer 1

In this example, you can simply enlarge the lifetime of y by removing the scope introduced by the curly braces.

fn main() {
    let x;

    let y = 42;
    x = &y;

    println!("The value of 'x' is {}.", x);
}

Or, as others suggested, you can transfer the ownership from y to x , ie move the value from y to x , by removing the reference operator & from y :

fn main() {
    let x;
    {
        let y = 42;
        x = y;
    }

    println!("The value of 'x' is {}.", x);
}