reference/src/introduction.md

# Introduction

This book is the primary reference for the Rust programming language. It
provides three kinds of material:

  - Chapters that informally describe each language construct and their use.
  - Chapters that informally describe the memory model, concurrency model,
    runtime services, linkage model and debugging facilities.
  - Appendix chapters providing rationale and references to languages that
    influenced the design.

> **Note**: You may also be interested in the [grammar].

<div class="warning">

Warning: This book is incomplete. Documenting everything takes a
while. We have a [big issue] to track documentation for every Rust feature,
so check that out if you can't find something here.

</div>

## What *The Reference* is Not

This book does not serve as an introduction to the language. Background
familiarity with the language is assumed. A separate [book] is available to
help acquire such background familiarity.

This book also does not serve as a reference to the [standard library]
included in the language distribution. Those libraries are documented
separately by extracting documentation attributes from their source code. Many
of the features that one might expect to be language features are library
features in Rust, so what you're looking for may be there, not here.

Similarly, this book does not usually book the specifics of `rustc` as a
tool or of Cargo. `rustc` has its own [book][rustc book]. Cargo has a
[book][cargo book] that contains a [reference][cargo reference]. There are a few
pages such as [linkage] that still describe how `rustc` works.

This book also only serves as a reference to what is available in stable
Rust. For unstable features being worked on, see the [Unstable Book].

Finally, this book is not normative. It may include details that are
specific to `rustc` itself, and should not be taken as a specification for
the Rust language. We intend to produce such a book someday, and until then,
the reference is the closest thing we have to one.

## How to Use This Book

This book does not assume you are reading this book sequentially. Each
chapter generally can be read standalone, but will cross-link to other chapters
for facets of the language they refer to, but do not discuss.

There are two main ways to read this document.

The first is to answer a specific question. If you know which chapter answers
that question, you can jump to that chapter in the table of contents. Otherwise,
you can press `s` or the click the magnifying glass on the top bar to search for
keywords related to your question. For example, say you wanted to know when a
temporary value created in a let statement is dropped. If you didn't already
know that the [lifetime of temporaries] is defined in the [expressions chapter],
you could search "temporary let" and the first search result will take you to
that section.

The second is to generally improve your knowledge of a facet of the language.
In that case, just browse the table of contents until you see something you
want to know more about, and just start reading. If a link looks interesting,
click it, and read about that section.

That said, there is no wrong way to read this book. Read it however you feel
helps you best.

### Conventions

Like all technical books, this book has certain conventions in how it displays
information. These conventions are documented here.

* Statements that define a term contain that term in *italics*. Whenever that
  term is used outside of that chapter, it is usually a link to the section that
  has this definition.

  An *example term* is an example of a term beind defined.

* Notes that contain useful information about the state of the book or point out
  useful, but mostly out of scope, information are in blockquotes that start with
  the word "Note:" in **bold**.

  > Note: This is an example note.

* Warnings that show unsound behavior in the language or possibly confusing
  interactions of language features are in a special warning box.

  <div class="warning">

  Warning: This is an example warning.

  </div>

* Code snippets inline in the text are inside `<code>` tags.

  Longer code examples are in a syntax highlighted box that has controls for
  copying, executing, and showing hidden lines in the top right corner.

  ```rust
  # // This is a hidden line.
  fn main() {
      println!("This is a code example");
  }
  ```

* The grammar and lexical structure is in blockquotes with either "Lexer" or
  "Syntax" in **bold** as the first line in <sup>superscript</sup>.

  > **<sup>Syntax</sup>**\
  > _ExampleGrammar_:\
  > &nbsp;&nbsp; &nbsp;&nbsp; `~` [_Expression_]\
  > &nbsp;&nbsp; | `box` [_Expression_]

## Contributing

We welcome contributions of all kinds.

You can contribute to this book by opening an issue or sending a pull
request to [the Rust Reference repository]. If this book does not answer
your question, and you think its answer is in scope of it, please do not
hesitate to file an issue or ask about it in the Rust docs channels on IRC or
discord. Knowing what people use this book for the most helps direct our
attention to making those sections the best that they can be.

[book]: ../book/index.html
[standard library]: ../std/index.html
[grammar]: ../grammar.html
[the Rust Reference repository]: https://github.com/rust-lang-nursery/reference/
[big issue]: https://github.com/rust-lang-nursery/reference/issues/9
[Unstable Book]: https://doc.rust-lang.org/nightly/unstable-book/
[_Expression_]: expressions.html
[cargo book]: ../cargo/index.html
[cargo reference]: ../cargo/reference/index.html
[expressions chapter]: expressions.html
[lifetime of temporaries]: expressions.html#temporary-lifetimes
[linkage]: linkage.html
[rustc book]: ../rustc/index.html