Transmute UB and `as` UB

playground.rs

#![allow(mutable_transmutes)]
use std::mem::transmute;

fn main() {
    let a: Vec<u64> = Vec::new();
    let r = &a;
    let r: &mut Vec<u64> = unsafe { transmute(r) };
    r.push(1488);
    println!("{:?}", a);
    
    let x = &666;
    let y: *mut i32 = x as *const _ as *mut i32;
    unsafe { *y = 5 };
    println!("{:?}", x);
}