Less powerful than it seems

The unsafe keyword does not allow you to break Rust.

use std::mem::transmute;

let orig = b"RUST";
let n: i32 = unsafe { transmute(orig) };

println!("{n}")

This slide should take about 10 minutes.

Suggested outline

Request that someone explains what std::mem::transmute does
Discuss why it doesn’t compile
Fix the code

Expected compiler output

   Compiling playground v0.0.1 (/playground)
error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
 --> src/main.rs:5:27
  |
5 |     let n: i32 = unsafe { transmute(orig) };
  |                           ^^^^^^^^^
  |
  = note: source type: `&[u8; 4]` (64 bits)
  = note: target type: `i32` (32 bits)

Suggested change

- let n: i32 = unsafe { transmute(orig) };
+ let n: i64 = unsafe { transmute(orig) };

Notes on less familiar Rust

the b prefix on a string literal marks it as byte slice (&[u8]) rather than a string slice (&str)