Change values via mutable reference

help
1

To make things easier, let me define a Node like this:

pub struct ListNode {
  pub val: i32,
  pub next: Option<Box<ListNode>>,
}

And I want to initialize this linked list using random numbers. Here is the code that does not work:

let mut l_list = None;
let mut iter_list = &mut l_list;
let x = get_random_number();

for _ in 0..x {
  if iter_list .is_none() {
      iter_list = &mut Some(Box::new(ListNode{val:x, next:None})); // ERROR!
  } else {
      iter_list.as_mut().unwrap().next = 
        Some(Box::new(ListNode{val:x,next:None}));
      iter_list = &mut iter_list .as_mut().unwrap().next;
  }
}

I am getting the following error:

error[E0716]: temporary value dropped while borrowed

Any idea to solve this w/o using pointers or a dummy node?

2

In your code, what is ref_list?

Also, you don't appear to be initializing it with random numbers, just one random number.

3

It might help people help you if you present that as a complete minimal program, inc. main() and all data declarations.

Also every answer to questions about linked lists in Rust has to include the question: Have you read this: Introduction - Learning Rust With Entirely Too Many Linked Lists ?

2 Likes
4

My bad, it is actually iter_list. I forgot to refactor them all.

5

BTW just ignore the random number thing since that is not important at all/

6

Wow that's a very nice doc! I will check it right away. Thx.

7

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