why can &Box<ListNode> be assigned to &ListNode?

Question

I found a variable of type &Box<ListNode> can be assigned to a variable of type &ListNode. They are different types, I don't known the mechanism behind this. I thought it might because of the Deref coercion. But I think Deref corecion only occurs in methold solution or parameter passing. I am not sure. Could someone help me? Thanks you very much.

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

 impl ListNode {
   #[inline]
   fn new(val: i32) -> Self {
     ListNode {
       next: None,
       val
     }
   }
 }

fn f1() {
  let node = ListNode::new(0);
  let mut ref_node:&ListNode = &node;
  let mut ref_box :&Box<ListNode>= &Box::new(ListNode::new(10));

  // why &Box<ListNode> can be assign to &ListNode?
  ref_node = ref_box; 
}

Answer 1

You are correct that this is because of Deref coercion. Coercions can be done at any coercion site which includes "let statements where an explicit type is given".