Unions

Unions are like enums, but you need to track the active field yourself:

1. #[repr(C)]
2. union MyUnion {
3. i: u8,
4. b: bool,
5. }

7. fn main() {
8. let u = MyUnion { i: 42 };
9. println!("int: {}", unsafe { u.i });
10. println!("bool: {}", unsafe { u.b });  // Undefined behavior!
11. }

Unions are very rarely needed in Rust as you can usually use an enum. They are occasionally needed for interacting with C library APIs.

If you just want to reinterpret bytes as a different type, you probably want std::mem::transmute or a safe wrapper such as the zerocopy crate.