Can't iterate RwLockReadGuard<Vec>

use std::thread;
use std::sync::{RwLock,Arc};
fn main() {
    let primes=Arc::new(RwLock::new(vec![2,3,5]));
    let primes2=primes.clone();
    let primes_w=primes.write().unwrap();
    let handle=thread::spawn(move || {
        let primes_r=primes2.read().unwrap();
        for i in &primes_r {
            println!("{:?}", i);
        }
    });
    primes_w.push(7);
    drop(primes_w);
    handle.join();
}