Mozilla is a company known for its mission to develop tools for and drive the open standards web, most notably through its flagship browser Firefox. Every browser today, including Firefox, is written in C++, some 1,29,00,992 lines of code for Firefox, and 44,90,488 lines of code for Chrome. This makes them fast, but it is inherently unsafe because the memory manipulations allowed by C and C++ are not checked for validity. If the code is written without the utmost programming discipline on the part of the developers, program crashes, memory leaks, segmentation faults, buffer overflows, and null pointers can occur at program execution. Some of these can result in serious security vulnerabilities, all too familiar in existing browsers. Rust is designed from the ground up to avoid those kind of problems.

Compared to C or C++, on the other side of the programming language spectrum we have Haskell, which is widely known to be a very safe and reliable language, but with very little or no control at the level of memory allocation and other hardware resources. We can plot different languages along this control that is safety axis, and it seems that when a language is safer, like Java compared to C++, it loses low-level control. The inverse is also true; a language that gives more control over resources like C++ provides much less safety.

Rust is made to overcome this dilemma by providing:

• High safety through its strong type system and smart compiler
• Deep but safe control over low-level resources (as much as C or C++), so it runs close to the hardware

Its main website, http://www.rust-lang.org/en-US/, contains links to installation instructions, docs and the Rust community.

Rust lets you specify exactly how your values are laid out in memory and how that memory is managed; that's why it works well at both ends of the control and safety line. This is the unique selling point of Rust, it breaks the safety-control dichotomy that, before Rust, existed among programming languages. With Rust they can be achieved together without losing performance.

Rust can accomplish both these goals without a garbage collector, in contrast to most modern languages like Java, C#, Python, Ruby, Go, and the like. In fact Rust doesn't even have a garbage collector yet (though an optional garbage collector is being designed).

Rust is a compiled language: the strict safety rules are enforced by the compiler, so they do not cause runtime overhead. As a consequence, Rust can work with a very small runtime, so it can be used for real-time or embedded projects and it can easily integrate with other languages or projects.

Rust is meant for developers and projects where performance and low-level optimizations are important, but also where a safe and stable execution environment is needed. The robustness of the language is specifically suited for projects where that is important, leading to less pressure in the maintenance cycle. Moreover, Rust adds a lot of high-level functional programming techniques to the language, so that it feels at the same time like a low-level and a high-level language.

Rust is not a revolutionary language with new cutting-edge features, but it incorporates a lot of proven techniques from older languages, while massively improving upon the design of C++ in matters of safe programming.

The Rust developers designed Rust to be a general purpose and multi-paradigm language; like C++, it is an imperative, structured and object-oriented language. Besides that, it inherits a lot from functional languages on the one hand, while also incorporating advanced techniques for concurrent programming on the other hand.

The typing of variables is static (because Rust is compiled) and strong. However, unlike in Java or C++, the developer is not forced to indicate types for everything; the Rust compiler is able to infer types in many cases.

C and C++ applications are known to be haunted by problems that often lead to program crashes or memory leaks, and which are notoriously difficult to debug and solve. Think about dangling pointers, buffer overflows, null pointers, segmentation faults, data races, and so on. The Rust compiler (called rustc) is very intelligent and can detect all these problems while compiling your code, thereby guaranteeing memory safety during execution. This is done by the compiler, retaining complete control over memory layout, but without needing the runtime burden of garbage collection (see Chapter 6, Using Traits and OOP in Rust). Of course, safety also implies much less possibility for security breaches.

Rust compiles to native code like Go and Julia but, in contrast to the other two, Rust needs no runtime with garbage collection. In this respect, it also differs from Java and the languages that run on the JVM, like Scala and Clojure. Most other popular modern languages, like .NET with C# and F#, JavaScript, Python, Ruby, Dart, and so on, all need a virtual machine and garbage collection for their execution.

Rust provides several mechanisms for concurrency and parallelism. The Standard Library gives a model that works with threads to perform work in parallel, where each thread maps to an operating system thread. They do not share heap memory, but communicate data through channels and data races are eliminated by the type system (see Chapter 8, Organizing Code and Macros). If needed in your project, several crates provide an actor-model approach with lightweight threads. These mechanisms make it easy for programmers to leverage the power of the many CPU cores available on current and future computing platforms.

The rustc compiler is completely self-hosted, which means it is written in Rust and can compile itself by using a previous version. It uses the LLVM compiler framework as its backend (for more info, see http://en.wikipedia.org/wiki/LLVM), and produces natively executable code that runs blazingly fast, because it compiles to the same low-level code as C++ ( see some benchmarks at http://benchmarksgame.alioth.debian.org/u64q/rust.php).

Rust is designed to be as portable as C++ and to run on widely-used hardware and software platforms. At present, it runs on Linux, macOS X, Windows, FreeBSD, Android, and iOS. For a more complete overview of where Rust can run, see https://forge.rust-lang.org/platform-support.html.

Rust can call C code as simply and efficiently as calling C code from C itself, and, conversely C code can also call Rust code (see Chapter 9, Concurrency - Coding for Multicore Execution).

Rust developers are called rustaceans.

Other Rust characteristics that will be discussed, in more detail in the later chapters are as follows:

• Variables are immutable by default (see Chapter 2, Using Variables and Types)
• Enums (see Chapter 4, Structuring Data and Matching Patterns)
• Pattern matching (see also Chapter 4, Structuring Data and Matching Patterns)
• Generics (see Chapter 5, Higher Order Functions and Error-Handling)
• Higher-order functions and closures (see also Chapter 5, Higher Order Functions and Error-Handling)
• An interface system called traits (see Chapter 6, Using Traits and OOP in Rust)
• A hygienic macro system (see Chapter 8, Organizing Code and Macros)
• Zero-cost abstractions, which means that Rust has higher-language constructs, but these do not have an impact on performance

In conclusion, Rust gives you ultimate power over memory allocation, as well as removing many security and stability problems commonly associated with native languages.

Dynamic languages such as Ruby or Python give you the initial speed of coding development, but the price is paid later in:

• Writing more tests
• Runtime crashes
• Production outages

The Rust compiler forces you to get a lot of things right from the beginning at compile time, which is the least expensive place to identify and fix bugs.

Rust's object orientation is not as explicit or evolved as common object-oriented languages such as Java, C# or Python, as it doesn't have classes. Compared with Go, Rust gives you more control over memory and resources and so it lets you code on a lower level. Go also works with a garbage collector; it has no generics and no mechanism to prevent data races between its goroutines used in concurrency. Julia is focused on numerical computing performance, works with a JIT compiler, and also doesn't give you that low-level control as Rust does.

Rust started out with version 1.0.0, and, at the time of writing, the current version is 1.20.0. Version numbers follow the semantic versioning principle (see http://semver.org/ for further information):

• Patch release: For bug fixes and other minor changes, increment the last number, for example 1.18.1
• Minor release: For new features which don't break existing features, increment the middle number, for example 1.19.0
• Major release: For changes which break backwards compatibility, increment the first number, for example 2.0.0

So, no breaking changes will occur during the current 1.n.m cycle versions, as this cycle is backward compatible; Rust projects which are developed in the older versions of this cycle will still compile in a more recent version. However, to be able to work with new features which are only contained in the more recent version, it is mandatory to compile your code to that specific version.

Rust has a very dynamic cycle of progression. Work is performed on three releases (called channels or builds simultaneously)--nightly, beta, and stable, and they follow a strict six-week release cycle like web browsers:

• The stable channel is the current stable release, which is advocated for Rust projects that are being used in production.
• The beta channel is where new features are deemed stable enough to be tested out in bigger, non-deployed projects.
• The nightly channel build contains the latest experimental features; it is produced from the master branch every 24 hours. You would use it only for experimentation.

The beta and stable channel builds are only updated as new features are backported to their branch. With this arrangement, Rust allows users to access new features and bug fixes quickly.

Here is a concrete example: 1.18 was released on 18th June, 2017, the 1.19-beta was released at the same time, and the master development branch was advanced to 1.20. Six weeks later, on 30th July, Rust 1.19 will come out of beta and become a stable release, 1.20 will be promoted to 1.21-beta, and the master will become the eventual 1.21.

Some features in an experimental stage can only work when the code contains an attribute #[feature]. These may not be used on the stable release channel, only on a beta or nightly release; an example is the box syntax (see chapter 2\code\references.rs).

Since its production release 1.0, Rust has enjoyed quite a steady uptake. This is manifest if you view a Google Trends survey:

In the well-known TIOBE Index (see https://www.tiobe.com/tiobe-index//), it reached 50th place in September 2015 and is now ranked in 37th position.

In the RedMonk ranking of programming languages (see http://redmonk.com/sogrady/2017/06/08/language-rankings-6-17/), it is ready to join the popularity of Lua, CoffeeScript, and Go.

Also, for two consecutive years, Rust was the most loved programing language on Stack Overflow (see https://insights.stackoverflow.com/survey/2017#most-loved-dreaded-and-wanted).

As a hallmark of its success, today, more than 50 companies are using Rust in production, see https://www.rust-lang.org/en-US/friends.html, amongst which are HoneyPot, Tilde, Chef, npm, Canonical, Coursera, and Dropbox.

It is clear from the previous sections that Rust can be used in projects that would normally use C or C++. Indeed, many regard Rust as a successor to, or a replacement for, C/C++. Although Rust is designed to be a systems language, due to its richness of constructs, it has a broad range of possible applications, making it an ideal candidate for applications that fall into one or all of the following categories:

• Client applications, like browsers
• Low-latency, high-performance systems, like device drivers, games and signal processing
• Highly distributed and concurrent systems, like server applications and microservices
• Real-time and critical systems, like operating systems or kernels
• Embedded systems (requiring a very minimal runtime footprint) or resource-constrained environments, like Raspberry Pi and Arduino, or robotics
• Tools or services that can't support the long warmup delays common in just-in-time (JIT) compiler systems and need instantaneous startup
• Web frameworks
• Large-scale, high-performance, resource intensive, and complex software systems

Rust is especially suitable when code quality is important, that is, for the following:

• Modestly-sized or larger development teams
• Code for long-running production use
• Code with a longer lifetime that requires regular maintenance and refactoring
• Code for which you would normally write a lot of unit tests to safeguard