Rust (programming language)

Paradigm Multi-paradigm: compiled, concurrent, functional, imperative, structured, generic
Designed by Graydon Hoare (original),
Rust project developers (later)
Developer Rust project developers
First appeared July 7, 2010 (2010-07-07)
Stable release
1.28.0[1] / August 2, 2018 (2018-08-02)
Typing discipline Static, strong, inferred, nominal, linear
Implementation language Rust
OS Linux, macOS, Windows, FreeBSD, OpenBSD,[2] Redox, Android, iOS (partial)[3]
License MIT License or Apache License 2.0[4]
Filename extensions .rs, .rlib
Influenced by
Alef,[5] C#,[5] C++,[5] Cyclone,[5][6] Erlang,[5] Haskell,[5] Haxe,[5] Hermes,[5] Limbo,[5] Newsqueak,[5] NIL,[5] OCaml,[5] Ruby,[5] Scheme,[5] Standard ML,[5] Swift[5][7]
Crystal, Elm,[8] Idris,[9] Swift[10]

Rust is a systems programming language[11] sponsored by Mozilla[12] which describes it as a "safe, concurrent, practical language",[13] supporting functional and imperative-procedural paradigms. Rust is syntactically similar to C++, but its designers intend it to provide better memory safety while still maintaining performance.

Rust is free and open-source software, released under an MIT License, or Apache License 2.0. Its designers have refined the language through the experiences of writing the Servo web browser layout engine[14] and the Rust compiler. A large proportion of current commits to the project are from community members.[15]

Rust won first place for "most loved programming language" in the Stack Overflow Developer Survey in 2016, 2017, and 2018.[16][17][18]

Design and features

Rust is intended to be a language for highly concurrent and highly safe systems,[19] and "programming in the large", that is, creating and maintaining boundaries that preserve large-system integrity.[20] This has led to a feature set with an emphasis on safety, control of memory layout, and concurrency. Performance of idiomatic Rust is comparable to the performance of idiomatic C++.[21][22]


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. 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. Nearly every part of a function body is an expression,[23] even control flow operators. For example, the ordinary if expression also takes the place of C's ternary conditional. A function need not end with a return expression: in this case the last expression in the function creates the return value.

Memory safety

The system is designed to be memory safe, and it does not permit null pointers, dangling pointers, or data races in safe code.[24][25][26][27] Data values can only be initialized through a fixed set of forms, all of which require their inputs to be already initialized.[28] 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 if a pointer has Some value or None.[25] Rust also introduces added syntax to manage lifetimes, and the compiler reasons about these through its borrow checker.

Memory management

Rust does not use an automated garbage collection system like those used by Go, Java, or .NET Framework. Instead, memory and other resources are managed through resource acquisition is initialization (RAII), 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 also a concept of references (using the & symbol), which do 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.


Rust has an ownership system where all values have a unique owner where the scope of the value is the same as the scope of the owner.[29] 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. 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 let keyword. 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.[30] Variables assigned multiple times must be marked with the mut keyword.

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.

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. 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 impl keyword. 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.


The language grew out of a personal project started in 2006 by Mozilla employee Graydon Hoare,[13] who stated that the project was possibly named after the rust family of fungi.[31] Mozilla began sponsoring the project in 2009[13] and announced it in 2010.[32][33] The same year, work shifted from the initial compiler (written in OCaml) to the self-hosting compiler written in Rust.[34] Named rustc, it successfully compiled itself in 2011.[35] rustc uses LLVM as its back end.

The first numbered pre-alpha release of the Rust compiler occurred in January 2012.[36] Rust 1.0, the first stable release, was released on May 15, 2015.[37][38] Following 1.0, stable point releases are delivered every six weeks, while features are developed in nightly Rust and then tested with alpha and beta releases that last six weeks.[39]

In addition to 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.[40] Typestates were removed because in practice they found little use, though the same function can still be achieved with branding patterns.[41]

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.

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, the editor-in-chief of Dr Dobb's, Andrew Binstock, commented on Rust's chances to become a competitor to C++, as well as 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 changed repeatedly between versions.[42]

Rust was the third most loved programming language in the 2015 Stack Overflow annual survey,[43] and took first place in 2016, 2017, and 2018.[44][45][46]

The language is referenced in The Book of Mozilla as "oxidised metal."

Code examples

Hello World

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

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

Factorial function


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


fn factorial(i: u64) -> u64 {
    let mut acc = 1;
    for num in 2..=i {
        acc *= num;

Using Iterators

fn factorial(i: u64) -> u64 {

Projects using Rust

The Rust compiler is written in Rust.[34]

Other projects developed in Rust include:

Web browser oriented:

Build tool oriented:

Operating system oriented:

Other projects:

See also


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  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 "The Rust Reference: Appendix: Influences". Retrieved July 14, 2017. Rust is not a particularly original language, with design elements coming from a wide range of sources. Some of these are listed below (including elements that have since been removed): SML, OCaml [...] C++ [...] ML Kit, Cyclone [...] Haskell [...] Newsqueak, Alef, Limbo [...] Erlang [...] Swift [...] Scheme [...] C# [...] Ruby [...] NIL, Hermes
  5. "Note Research: Type System". 2015-02-01. Retrieved 2015-03-25. Papers that have had more or less influence on Rust, or which one might want to consult for inspiration or to understand Rust's background. [...] Region based memory management in Cyclone [...] Safe memory management in Cyclone
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