How to : returning values referencing local Rc?

help
1

Things like this:

struct Test<'a> {
    a: Rc<String>,
    b: &'a str
}

fn test(v: &str) -> Test {
    let t = Rc::new(v.to_string());
    Test {
        a: t.clone(),
        b: &t
    }
}

Certainly the above code wont compile because b reference t which is local,
but It might be done like this,

#[derive(Default)]
struct Test<'a> {
    a: Rc<String>,
    b: &'a str,
}

fn test(v: &str) -> Test {
    let t = Rc::new(v.to_string());
    let te = Test::default();
    te.a = t.clone();
    te.b = &te.a;
    te
}

But, what if te.b does not derive Default ?

2

The code you provide won't compile. But I'm not clear why you would want to do this. Can you explain a bit more about your desired use case?

3

Just think of a struct, where some members reference others, like

struct Foo<T> {
    a: Rc<T>,
    b: sth. referencing a
}

Think of construct the struct when b does not derive default, that is why I want to do this.

4

This is a self-referential struct, and it's not possible in Rust.

It's not safe, because the borrow checker operates on fields individually, and would allow a to be replaced while b points to the old value.

5

In general, self-referential structs are an anti-pattern in rust because moving the struct in memory would cause the references to become invalid.

Some additional reading on the topic:

The short answer is that you can't create self-referential structs without significant restrictions and challenges. However, it turns out it's rarely truly necessary, so again, I'd ask why you need a pattern like this. What problem are you trying to solve?

6

Thanks for that.

So I am going to find another way out.