developers have turned off some compiler safety features and have to write correct code by themselves. It means the compiler no longer enforces Rust's memory-safety rules. 30.2 Dereferenciación de Punteros s = String::from("¡cuidado!"); let r1 = &mut s as *mut String; let r2 = r1 as *const String; // SAFETY: r1 and r2 were obtained from references and so are guaranteed to // be non-null and properly aligned add_to_counter(inc: u32) { // SAFETY: There are no other threads which could be accessing `COUNTER`. unsafe { COUNTER += inc; } } fn main() { add_to_counter(42); // SAFETY: There are no other threads