Rust (programming language)

Rust

The official Rust logo
Paradigms	Multi-paradigm: concurrent, functional, generic, imperative, structured
Designed by	Graydon Hoare
Developer	Mozilla Research
First appeared	July 7, 2010 (2010-07-07)
Stable release	1.83.0  / November 28, 2024 (November 28, 2024)
Typing discipline	Affine, inferred, nominal, static, strong
Implementation language	Rust
Platform	ARM, IA-32, x86-64, MIPS, PowerPC, SPARC, RISC-V, WebAssembly
OS	Linux, macOS, Windows, FreeBSD, OpenBSD, Redox, Android, iOS
License	MIT or Apache 2.0
Filename extensions	.rs, .rlib (metadata file)
Website	www.rust-lang.org
Influenced by
Alef C# C++ Cyclone Erlang Haskell Limbo Newsqueak OCaml Ruby Scheme Standard ML Swift
Influenced
Crystal Elm Idris Spark Swift Project Verona Zig PHP

Rust is a multi-paradigm programming language designed for performance and safety, especially safe concurrency. Rust is syntactically similar to C++, but can guarantee memory safety by using a borrow checker to validate references. Rust achieves memory safety without garbage collection, and reference counting is optional.

Rust was originally designed by Graydon Hoare at Mozilla Research, with contributions from Dave Herman, Brendan Eich, and others. The designers refined the language while writing the Servo layout or browser engine, and the Rust compiler. It has gained increasing use in industry, and Microsoft has been experimenting with the language for secure and safety-critical software components.

Rust has been voted the "most loved programming language" in the Stack Overflow Developer Survey every year since 2016.

History

An example of compiling a Rust program

The language grew out of a personal project begun in 2006 by Mozilla employee Graydon Hoare, who stated that the project was possibly named after the rust family of fungi. Mozilla began sponsoring the project in 2009 and announced it in 2010. The same year, work shifted from the initial compiler (written in OCaml) to the LLVM-based self-hosting compiler written in Rust. Named rustc, it successfully compiled itself in 2011.

The first numbered pre-alpha release of the Rust compiler occurred in January 2012. Rust 1.0, the first stable release, was released on May 15, 2015. Following 1.0, stable point releases are delivered every six weeks, while features are developed in nightly Rust with daily releases, then tested with beta releases that last six weeks. Every 2 to 3 years, a new Rust "Edition" is produced. This is to provide a easy reference point for changes due to the frequent nature of Rust's Train release schedule, as well as to provide a window to make breaking changes. Editions are largely compatible.

Along with conventional static typing, before version 0.4, Rust also supported typestates. The typestate system modeled assertions before and after program statements, through use of a special check statement. Discrepancies could be discovered at compile time, rather than at runtime, as might be the case with assertions in C or C++ code. The typestate concept was not unique to Rust, as it was first introduced in the language NIL. Typestates were removed because in practice they were little used, though the same functionality can be achieved by leveraging Rust's move semantics.

The style of the object system changed considerably within versions 0.2, 0.3 and 0.4 of Rust. Version 0.2 introduced classes for the first time, and version 0.3 added several features, including destructors and polymorphism through the use of interfaces. In Rust 0.4, traits were added as a means to provide inheritance; interfaces were unified with traits and removed as a separate feature. Classes were also removed and replaced by a combination of implementations and structured types.

Starting in Rust 0.9 and ending in Rust 0.11, Rust had two built-in pointer types: ~ and @, simplifying the core memory model. It reimplemented those pointer types in the standard library as Box and (the now removed) Gc.

In January 2014, before the first stable release, Rust 1.0, the editor-in-chief of Dr. Dobb's, Andrew Binstock, commented on Rust's chances of becoming a competitor to C++ and to the other up-and-coming languages D, Go, and Nim (then Nimrod). According to Binstock, while Rust was "widely viewed as a remarkably elegant language", adoption slowed because it repeatedly changed between versions.

Rust has a foreign function interface (FFI) that can be called from e.g. C language, and can call C. While calling C++ has historically been problematic (from any language), Rust has a library, CXX, to allow calling to or from C++, and "CXX has zero or negligible overhead".

In August 2020, Mozilla laid off 250 of its 1,000 employees worldwide as part of a corporate restructuring caused by the long-term impact of the COVID-19 pandemic. Among those laid off were most of the Rust team, while the Servo team was completely disbanded. The event raised concerns about the future of Rust.

In the following week, the Rust Core Team acknowledged the severe impact of the layoffs and announced that plans for a Rust foundation were underway. The first goal of the foundation would be taking ownership of all trademarks and domain names, and also take financial responsibility for their costs.

On February 8, 2021 the formation of the Rust Foundation was officially announced by its five founding companies (AWS, Huawei, Google, Microsoft, and Mozilla).

On April 6, 2021, Google announced support for Rust within Android Open Source Project as an alternative to C/C++.

Syntax

Here is a simple "Hello, World!" program written in Rust. The println! macro prints the message to standard output.

fn main() {
    println!("Hello, World!");
}

The concrete syntax of Rust is similar to C and C++, with blocks of code delimited by curly brackets, and control flow keywords such as if, else, while, and for, although the specific syntax for defining functions is more similar to Pascal. Not all C or C++ keywords are implemented, however, and some Rust functions (such as the use of the keyword match for pattern matching) will be less familiar to those versed in these languages. Despite the superficial resemblance to C and C++, the syntax of Rust in a deeper sense is closer to that of the ML family of languages and the Haskell language. Nearly every part of a function body is an expression, even control flow operators. For example, the ordinary if expression also takes the place of C's ternary conditional, an idiom used by ALGOL 60. As in Lisp, a function need not end with a return expression: in this case if the semicolon is omitted, the last expression in the function creates the return value, as seen in the following recursive implementation of the factorial function:

fn factorial(i: u64) -> u64 {
    match i {
        0 => 1,
        n => n * factorial(n-1)
    }
}

The following iterative implementation uses the ..= operator to create an inclusive range:

fn factorial(i: u64) -> u64 {
    (2..=i).product()
}

Features

A presentation on Rust by Emily Dunham from Mozilla's Rust team (linux.conf.au conference, Hobart, 2017)

Rust is intended to be a language for highly concurrent and highly safe systems, and programming in the large, that is, creating and maintaining boundaries that preserve large-system integrity. This has led to a feature set with an emphasis on safety, control of memory layout, and concurrency.

Memory safety

Rust is designed to be memory safe, and it does not permit null pointers, dangling pointers, or data races in safe code. Data values can be initialized only through a fixed set of forms, all of which require their inputs to be already initialized. To replicate the function in other languages of pointers being either valid or NULL, such as in linked list or binary tree data structures, the Rust core library provides an option type, which can be used to test whether a pointer has Some value or None. Rust also introduces added syntax to manage lifetimes, and the compiler reasons about these through its borrow checker. Unsafe code that can subvert some of these restrictions may be written using the language's unsafe keyword.

Memory management

Rust does not use an automated garbage collection system. Instead, memory and other resources are managed through the resource acquisition is initialization (RAII) convention, with optional reference counting. Rust provides deterministic management of resources, with very low overhead. Rust also favors stack allocation of values and does not perform implicit boxing.

There is the concept of references (using the & symbol), which does not involve run-time reference counting. The safety of using such pointers is verified at compile time by the borrow checker, preventing dangling pointers and other forms of undefined behavior. Additionally, Rust's type system separates shared, immutable pointers of the form &T from unique, mutable pointers of the form &mut T. However, a mutable pointer can be coerced to an immutable pointer, but not vice versa.

Ownership

Rust has an ownership system where all values have a unique owner, and the scope of the value is the same as the scope of the owner. Values can be passed by immutable reference, using &T, by mutable reference, using &mut T, or by value, using T. At all times, there can either be multiple immutable references or one mutable reference (an implicit readers–writer lock). The Rust compiler enforces these rules at compile time and also checks that all references are valid.

Types and polymorphism

The type system supports a mechanism similar to type classes, called "traits", inspired directly by the Haskell language. This is a facility for ad hoc polymorphism, achieved by adding constraints to type variable declarations. Other features from Haskell, such as higher-kinded polymorphism, are not yet supported.

Rust features type inference for variables declared with the keyword let. Such variables do not require a value to be initially assigned to determine their type. A compile time error results if any branch of code leaves the variable without an assignment. Variables assigned multiple times must be marked with the keyword mut.

Functions can be given generic parameters, which usually require the generic type to implement a certain trait or traits. Within such a function, the generic value can only be used through those traits. This means that a generic function can be type-checked as soon as it is defined. This is in contrast to C++ templates, which are fundamentally duck typed and cannot be checked until instantiated with concrete types. C++ concepts address the same issue and are part of C++20, though they still don't allow the C++ compiler to typecheck a template without concrete instantiation.

However, the implementation of Rust generics is similar to the typical implementation of C++ templates: a separate copy of the code is generated for each instantiation. This is called monomorphization and contrasts with the type erasure scheme typically used in Java and Haskell. Type erasure is also available in Rust by using the keyword dyn. The benefit of monomorphization is optimized code for each specific use case; the drawback is increased compile time and size of the resulting binaries.

The object system within Rust is based around implementations, traits and structured types. Implementations fulfill a role similar to that of classes within other languages and are defined with the keyword impl. Inheritance and polymorphism are provided by traits; they allow methods to be defined and mixed in to implementations. Structured types are used to define fields. Implementations and traits cannot define fields themselves, and only traits can provide inheritance. Among other benefits, this prevents the diamond problem of multiple inheritance, as in C++. In other words, Rust supports interface inheritance, but replaces implementation inheritance with composition; see composition over inheritance.

Components

Rust features a large number of components that extend the Rust feature set and make Rust development easier. Component installation is typically managed by rustup, a Rust toolchain installer developed by the Rust project.

Cargo

Cargo is Rust's build system and package manager. Cargo handles (among other things) building code, downloading dependencies, and building dependencies.

The dependencies for a Rust package are specified in a Cargo.toml file along with version requirements, telling Cargo which versions of the dependency are compatible with the package. By default, Cargo sources its dependencies from the user-contributed registry crates.io but Git repositories and packages in the local filesystem can be specified as dependencies, too.

Cargo also acts as a wrapper to clippy and other Rust components to facilitate the invocation of these tools. It requires projects to follow a certain directory structure "to make working with Rust packages easier".

Rustfmt

Rustfmt is a code formatter for Rust. It takes Rust source code as input and changes the whitespace and indentation to produce formatted code in accordance to the Rust style guide. Rustfmt can also check whether the input is correctly formatted.

Clippy

Clippy is Rust's built in linting tool to improve the correctness, performance, and readability of Rust code. As of 2021, Clippy has more than 450 rules, which can be browsed online and filtered by category. Some rules are disabled by default.

RLS

RLS is a language server that provides IDEs and text editors with more information about a Rust project. It provides linting checks via Clippy, formatting via Rustfmt, automatic code completion via Racer, among other functions. Development of Racer was slowed down in favor of rust-analyzer.

Language extensions

It is possible to extend the Rust language using the procedural macro mechanism.

Procedural macros use Rust functions that run at compile time to modify the token stream that is processed by the compiler. This complements the user defined macro mechanism which uses pattern matching to achieve similar goals.

Procedural macros come in three flavors:

• Function-like macros custom!(...)
• Derive macros #[derive(CustomDerive)]
• Attribute macros #[CustomAttribute]

The println! macro is an example of a function-like macro and serde_derive is a commonly used library for generating code for reading and writing data in many formats such as JSON. Attribute macros are commonly used for language bindings such as the extendr library for Rust bindings to R.

The following code shows the use of the Serialize, Deserialize and Debug derive procedural macros to implement JSON reading and writing as well as the ability to format a structure for debugging.

use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug)]
struct Point {
    x: i32,
    y: i32,
}

fn main() {
    let point = Point { x: 1, y: 2 };

    let serialized = serde_json::to_string(&point).unwrap();
    println!("serialized = {}", serialized);

    let deserialized: Point = serde_json::from_str(&serialized).unwrap();
    println!("deserialized = {:?}", deserialized);
}

Performance

Rust aims "to be as efficient and portable as idiomatic C++, without sacrificing safety". Since Rust utilizes LLVM, any performance improvements in LLVM also carry over to Rust.

Adoption

Some Rust users refer to themselves as Rustaceans (a pun on "crustacean") and use Ferris as their unofficial mascot.

See also: Category:Rust (programming language) software

Rust was the third-most-loved programming language in the 2015 Stack Overflow annual survey and took first place for 2016–2020.

Web browser

A web browser and several related components are being written in Rust. Firefox, for example, has two projects written in Rust, including Servo, a parallel web-browser engine developed by Mozilla in collaboration with Samsung and Quantum, which is composed of several sub projects, for improving the Gecko web-browser engine, which is also developed by Mozilla.

Operating systems

Operating systems and OS-level components written in Rust include:

• Redox: a "full-blown Unix-like operating system" including a microkernel
• Stratis: a file system manager for Fedora and RHEL 8
• Google Fuchsia: a capability-based operating system

Other

• exa, a "modern replacement for ls"
• Microsoft Azure IoT Edge, a platform used to run Azure services and artificial intelligence on IoT devices, has components implemented in Rust
• OpenDNS uses Rust in two of its components
• Tor, an anonymity network, written in C originally, is experimenting with porting to Rust for its security features
• Deno, a secure runtime for JavaScript and TypeScript, is built with V8, Rust, and Tokio
• Prisma, an ORM for JavaScript, TypeScript, and Go, recently ported its query engine to Rust for its version 2 release.
• Discord, a chat service targeted towards gamers, uses Rust for portions of its backend, as well as client-side video encoding
• TerminusDB, an open source graph database designed for collaboratively building and curating knowledge graphs
• Ruffle, an open-source SWF emulator written in Rust

Governance

Rust Foundation

Formation	February 8, 2021 (2021-02-08)
Founders	Amazon Web Services Google Huawei Microsoft Mozilla Foundation
Type	Nonprofit organization
Location	United States
Chairperson	Shane Miller
Executive Director	Ashley Williams (interim)
Website	foundation.rust-lang.org

The Rust Foundation is a non-profit membership organization incorporated in Delaware, United States, with the primary purposes of supporting the maintenance and development of the language, cultivating the Rust project team members and user communities, managing the technical infrastructure underlying the development of Rust, and managing and stewarding the Rust trademark.

It was established on February 8, 2021, with five founding corporate members (Amazon Web Services, Huawei, Google, Microsoft, and Mozilla).

The foundation's board is chaired by Shane Miller. Its interim Executive Director is Ashley Williams.

Development

Rust conferences include:

• RustConf: an annual conference in Portland, Oregon. Held annually since 2016 (except in 2020 because of the COVID-19 pandemic).
• Rust Belt Rust: a #rustlang conference in the Rust Belt
• RustFest: Europe's @rustlang conference
• RustCon Asia
• Rust LATAM
• Oxidize Global

See also

• Comparison of programming languages

External links

• Official website
• Rust-lang on GitHub