Advanced Magic (unsafe)

Almost everything you have learned in Rust comes with a built-in safety helper. Rust watches your back, checks your work, and stops scary mistakes before your program ever runs. But did you know there is one special, tiny doorway where Rust says, “Okay… I trust you. You’re on your own here”? It’s called unsafe. ⚡

What is unsafe?

Most of your Rust code is safe code. Safe code is like riding a bike with training wheels — you can wobble, but you won’t crash. Rust keeps you steady.

unsafe is a special block where you take the training wheels off for one tiny part of your ride. You can do a few risky things that Rust normally won’t allow, like using raw pointers (super-direct arrows to a spot in the computer’s memory). With great power comes great responsibility.

Who uses it, and when?

Honestly? Almost nobody, almost never. Most Rust programmers go a long, long time without writing a single unsafe block. It is used by experts building the deep, tricky parts that everything else stands on — like talking directly to the computer’s hardware.

Here is what a tiny unsafe block looks like. You don’t need to understand it — just notice the special word.

fn main() {
    let mut number = 5;
    let pointer = &mut number as *mut i32; // a raw pointer (a direct arrow!)

    unsafe {
        *pointer = 10; // only allowed inside unsafe
    }

    println!("number is now {number}");
}

Quick quiz