如何在没有赋值的情况下声明静态可变变量？

I tried the following

我尝试了以下内容

struct mbuf
{
  cacheline: *mut [u64],               // great amount of rows follows below
  // ..........
}
static mut arr: [mbuf; 32];                // Q1 my main aim
// something as before but using Vec;      // Q2 also main aim

fn main() {
 // let static mut arr: [mbuf; 32];        // Q3 also doesn't work
 // static mut arr: [mbuf; 32];            // Q3 also doesn't work
}
struct mbuf