如何使用 Rust 中的 Ref 字段初始化结构？

Question

If has a Stuct A and a Struct B

struct B {}

stuct A<'a> {
 id: i32,
 b: &'a B
}
impl A<'_> {
 fn new() -> A {
   id: 3,
   b: //(I Have No B at moment, hwo to create a A without B )
 }
}

I would like to create A, then assign &B to A.

Answer 1

Why not use Option ? Rust doesn't have null, thankfully.