Rust (programming language)

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Rust programming language black logo.svg
Official Rust logo
ParadigmsMulti-paradigm: concurrent, functional, generic, imperative, structured
Designed byGraydon Hoare
First appearedJuly 7, 2010; 10 years ago (2010-07-07)
Stable release
1.49.0[1] Edit this on Wikidata / 31 December 2020; 18 days ago (31 December 2020)
Typing disciplineAffine, inferred, nominal, static, strong
Implementation languageRust
PlatformARM, IA-32, x86-64, MIPS, PowerPC, SPARC, RISC-V[2][3]
OSLinux, macOS, Windows, FreeBSD, OpenBSD,[4] Redox, Android, iOS[5]
LicenseMIT or Apache 2.0[6]
Filename, .rlib (metadata file)
Influenced by
Alef,[7] C#,[7] C++,[7] Cyclone,[7][8] Erlang,[7] Haskell,[7] Limbo,[7] Newsqueak,[7] OCaml,[7] Ruby,[7] Scheme,[7] Standard ML,[7] Swift[7][9]
Crystal, Elm,[10] Idris,[11] Spark,[12] Swift,[13] Project Verona,[14] Zig

Rust is a multi-paradigm programming language designed for performance and safety, especially safe concurrency.[15][16] Rust is syntactically similar to C++,[17] but can guarantee memory safety by using a borrow checker to validate references.[18] Rust achieves memory safety without garbage collection, and reference counting is optional.[19][20]

Rust was originally designed by Graydon Hoare at Mozilla Research, with contributions from Dave Herman, Brendan Eich, and others.[21][22] The designers refined the language while writing the Servo layout or browser engine,[23] 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.[24][25]

Rust has been voted the "most loved programming language" in the Stack Overflow Developer Survey every year since 2016.[26]


A bright orange crab icon
Some Rust users refer to themselves as Rustaceans (a pun on "crustacean") and use Ferris as their unofficial mascot.[27]

The language grew out of a personal project begun in 2006 by Mozilla employee Graydon Hoare,[16] who stated that the project was possibly named after the rust family of fungi.[28] Mozilla began sponsoring the project in 2009[16] and announced it in 2010.[29][30] The same year, work shifted from the initial compiler (written in OCaml) to the LLVM-based self-hosting compiler written in Rust.[31] Named rustc, it successfully compiled itself in 2011.[32]

The first numbered pre-alpha release of the Rust compiler occurred in January 2012.[33] Rust 1.0, the first stable release, was released on May 15, 2015.[34][35] Following 1.0, stable point releases are delivered every six weeks, while features are developed in nightly Rust and then tested with beta releases that last six weeks.[36]

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 when a program was running, 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.[37] Typestates were removed because in practice they were little used, though the same function can still be achieved with a branding pattern.[38]

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, with version 0.3 adding 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, replaced by a combination of implementations and structured types.[citation needed]

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 to become a competitor to C++ and to the other upcoming 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.[39]

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".[40]

Mozilla layoffs and a Rust foundation[edit]

In August 2020, Mozilla laid off 250 employees worldwide as part of a corporate restructure caused by the long-term impact of the COVID-19 pandemic. The number corresponded to 25% of all its staff.[41][42] Among these employees were most of the Rust team,[43] while the Servo team was completely disbanded.[44] The event raised concerns about the future of Rust.[45]

In the following week, the Rust Core Team acknowledged the severe impact of the layoffs and announced that plans for a Rust foundation were undergoing. The first goal of the foundation would be taking ownership of all trademarks and domain names, and also take financial responsibility for their costs.[46]

In November 2020, Amazon Web Services announced its commitment to the Rust continuity by hiring some people who had a close relationship with the Rust language development. AWS said to be expanding the use of Rust in the development of its own products.[47]


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,[48] 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 {


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

Rust is intended to be a language for highly concurrent and highly safe systems,[49] and programming in the large, that is, creating and maintaining boundaries that preserve large-system integrity.[50] This has led to a feature set with an emphasis on safety, control of memory layout, and concurrency.

Memory safety[edit]

Rust is designed to be memory safe, and it does not permit null pointers, dangling pointers, or data races in safe code.[51][52][53] Data values can be initialized only through a fixed set of forms, all of which require their inputs to be already initialized.[54] 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.[52] Rust also introduces added syntax to manage lifetimes, and the compiler reasons about these through its borrow checker. Unsafe code which can subvert some of these restrictions may be written using the language's unsafe keyword.[18]

Memory management[edit]

Rust does not use an automated garbage collection system. Instead, memory and other resources are managed through the resource acquisition is initialization (RAII) convention,[55] with optional reference counting. Rust provides deterministic management of resources, with very low overhead.[citation needed] 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.


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.[56][57] 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[edit]

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 fails to assign a value to the variable.[58] 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.


Performance of idiomatic Rust is comparable to the performance of idiomatic C++.[59][60]


Rust was the third-most-loved programming language in the 2015 Stack Overflow annual survey[61] and took first place for 2016–2020.[62]

Web browser[edit]

A web browser and several related components are being written in Rust, including:

Operating systems[edit]

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



Rust conferences include:

See also[edit]


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External links[edit]