How to Use Union Types in Rust

Unsafe Ffi

2026-04-17T12:05:42+00:00

Define a union with the `union` keyword and access its fields inside an `unsafe` block to manage overlapping memory safely.

Union types in Rust are defined using the union keyword to create a type where all fields share the same memory address, allowing only one field to be active at a time. Because accessing union fields is unsafe, you must wrap the access in an unsafe block to prevent memory safety violations.

union MyUnion {
    integer: i32,
    float: f32,
}

fn main() {
    let u = MyUnion { integer: 42 };
    unsafe {
        println!("Integer: {}", u.integer);
    }
}