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# The Rustonomicon

#### The Dark Arts of Unsafe Rust

> 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.

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

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][trpl]*, 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][trpl] 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.

This book exists primarily as a high-level companion to [The Reference][ref].
Where The Reference exists to detail the syntax and semantics of every part of
the language, The Rustonomicon exists to describe how to use those pieces together,
and the issues that you will have in doing so.

The Reference will tell you the syntax and semantics of references, destructors, and
unwinding, but it won't tell you how combining them can lead to exception-safety
issues, or how to deal with those issues.

It should be noted that when The Rustonomicon was originally written, The
Reference was in a state of complete disrepair, and so many things that should
have been covered by The Reference were originally only documented here. Since
then, The Reference has been revitalized and is properly maintained, although
it is still far from complete. In general, if the two documents disagree, The
Reference should be assumed to be correct (it isn't yet considered normative,
it's just better maintained).

Topics that are within the scope of this book include: the meaning of (un)safety,
unsafe primitives provided by the language and standard library, techniques for
creating safe abstractions with those unsafe primitives, subtyping and variance,
exception-safety (panic/unwind-safety), working with uninitialized memory,
type punning, concurrency, interoperating with other languages (FFI),
optimization tricks, how constructs lower to compiler/OS/hardware primitives,
how to **not** make the memory model people angry, how you're **going** to make the
memory model people angry, and more.

The Rustonomicon is not a place to exhaustively describe the semantics and guarantees
of every single API in the standard library, nor is it a place to exhaustively describe
every feature of Rust.

[trpl]: ../book/index.html
[ref]: ../reference/index.html