Code shared from the Rust Playground

playground.rs

#![feature(core_intrinsics)]

use std::intrinsics::discriminant_value;
use std::mem::size_of;

#[derive(Debug)]
#[allow(dead_code)]
enum E {
    A = 0x1000_0000,
    B = 0,
}

fn main() {
    let x = &0xffff_ffffu32 as *const u32 as *const E;
    let z = unsafe { std::ptr::read(x) };
    assert_eq!(size_of::<E>(), size_of::<u32>());
    let actual_discriminant = unsafe { discriminant_value(&z) };
    println!("{:?}, discriminant 0x{:x}", z, actual_discriminant);
}