# The Rustonomicon

#### The Dark Arts of Advanced and Unsafe Rust Programming

> Instead of the programs I had hoped for, there came only a shuddering blackness and ineffable loneliness; and I saw at last a fearful truth which no one had ever dared to breathe before — the unwhisperable secret of secrets — The fact that this language of stone and stridor is not a sentient perpetuation of Rust as London is of Old London and Paris of Old Paris, but that it is in fact quite `unsafe`, its sprawling body imperfectly embalmed and infested with queer animate things which have nothing to do with it as it was in compilation.

This book digs into all the awful details that you need to understand when writing Unsafe Rust programs.

> THE KNOWLEDGE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF UNLEASHING INDESCRIBABLE HORRORS THAT SHATTER YOUR PSYCHE AND SET YOUR MIND ADRIFT IN THE UNKNOWABLY INFINITE COSMOS.

Should you wish a long and happy career of writing Rust programs, you should turn back now and forget you ever saw this book. It is not necessary. However if you intend to write unsafe code — or just want to dig into the guts of the language — this book contains lots of useful information.

Unlike The Rust Programming Language, we will be assuming considerable prior knowledge. In particular, you should be comfortable with basic systems programming and Rust. If you don't feel comfortable with these topics, you should consider reading The Book first. That said, we won't assume you have read it, and we will take care to occasionally give a refresher on the basics where appropriate. You can skip straight to this book if you want; just know that we won't be explaining everything from the ground up.

We're going to dig into exception-safety, pointer aliasing, memory models, compiler and hardware implementation details, and even some type-theory. Much text will be devoted to exotic corner cases that no one should ever have to care about, but suddenly become important because we wrote `unsafe`.

We will also be spending a lot of time talking about the different kinds of safety and guarantees that programs could care about.