Rust (programming language): Difference between revisions

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'''Rust''' is a text-based [[General-purpose programming language|general-purpose]] [[programming language]] emphasizing [[Computer performance|performance]], [[type safety]], and [[Concurrency (computer science)|concurrency]]. It enforces [[memory safety]], meaning that all [[Reference (computer science)|references]] point to valid memory. It does so without a conventional [[Garbage collection (computer science)|garbage collector]]; instead, memory safety errors and [[data race]]s are prevented by the "borrow checker", which tracks the [[object lifetime]] of references [[Compiler|at compile time]].

Rust supports multiple [[programming paradigm]]s. It was influenced by ideas from [[functional programming]], including [[Immutable object|immutability]], [[higher-order function]]s, [[algebraic data type]]s, and [[pattern matching]]. It also supports [[object-oriented programming]] via structs, [[Union type|enums]], traits, and methods.

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=== Variables ===

[[Variable (computer science)|Variables]] in Rust are defined through the {{rust|let}} keyword.{{sfn|Klabnik|Nichols|2023|p=32}} The example below assigns a value to the variable with name {{coderust|foo}} of type {{rust|i32}} and outputs its value.

<syntaxhighlight lang="rust">

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</syntaxhighlight>

Variables are [[Immutable object|immutable]] by default, but adding the {{rust|mut}} keyword allows the variable to be mutated.{{sfn|Klabnik|Nichols|2023|pp=32-33}} The following example uses {{coderust|//}}, which denotes the start of a [[Comment (computer programming)|comment]].{{sfn|Klabnik|Nichols|2023|pp=49-50}}

<syntaxhighlight lang="rust">

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</syntaxhighlight>

Multiple {{coderust|let}} expressions can define multiple variables with the same name, known as [[variable shadowing]]. Variable shadowing allows transforming variables without having to name the variables differently.{{sfn|Klabnik|Nichols|2023|pp=34-36}} The example below declares a new variable with the same name that is double the original value:

<syntaxhighlight lang="rust">

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</syntaxhighlight>

==== {{coderust|if}} expressions ====

An {{rust|if}} [[conditional expression]] executes code based on whether the given value is {{coderust|true}}. {{rust|else}} can be used for when the value evaluates to {{coderust|false}}, and {{rust|else if}} can be used for combining multiple expressions.{{sfn|Klabnik|Nichols|2023|pp=50-53}}

<syntaxhighlight lang="rust">

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</syntaxhighlight>

==== {{coderust|while}} loops ====

<code>[[While loop|while]]</code> can be used to repeat a block of code while a condition is met.{{sfn|Klabnik|Nichols|2023|p=56}}

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</syntaxhighlight>

==== {{coderust|for}} loops and iterators ====

[[For loop]]s in Rust loop over elements of a collection.{{sfn|Klabnik|Nichols|2023|pp=57-58}}

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<syntaxhighlight lang="rust">

(1..=100).filter(|&x: i8| -> bool { x % 3 == 0 }).sum()

</syntaxhighlight>

==== {{coderust|loop}} and {{coderust|break}} statements ====

More generally, the {{rust|loop}} keyword allows repeating a portion of code until a {{rust|break}} occurs. {{rust|break}} may optionally exit the loop with a value. In the case of nested loops, labels denoted by {{rust|'label_name}} can be used to break an outer loop rather than the innermost loop.{{sfn|Klabnik|Nichols|2023|pp=54-56}}

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=== Types ===

Rust is [[strongly typed]] and [[statically typed]], meaning that the types of all variables must be known at compilation time. Assigning a value of a particular type to a differently typed variable causes a [[compilation error]]. [[Type inference]] is used to determine the type of variables if unspecified.{{sfn|Klabnik|Nichols|2019|pp=24}}

The type <code>()</code>, called the "unit type" in Rust, is a concrete type that has exactly one value. It occupies no memory (as it represents the absence of value). All functions that do not have an indicated return type implicitly return <code>()</code>. It is similar to {{cpp|void}} in other C-style languages, however {{cpp|void}} denotes the absence of a type and cannot have any value.

The default integer type is {{rust|i32}}, and the default [[floating point]] type is {{rust|f64}}. If the type of a [[Literal (computer programming)|literal]] number is not explicitly provided, it is either inferred from the context or the default type is used.{{sfn|Klabnik|Nichols|2019|pp=36–38}}

==== Primitive types ====

[[Integer type]]s in Rust are named based on the [[signedness]] and the number of bits the type takes. For example, {{rust|i32}} is a signed integer that takes 32 bits of storage, whereas {{coderust|u8}} is unsigned and only takes 8 bits of storage. {{rust|isize}} and {{rust|usize}} take storage depending on the architecture of the computer that runs the code, for example, on computers with [[32-bit architecture]]s, both types will take up 32 bits of space.{{cn|date=August 2025}}

By default, integer literals are in base-10, but different [[radix|radices]] are supported with prefixes, for example, {{rust|0b11}} for [[binary number]]s, {{rust|0o567}} for [[octal]]s, and {{rust|0xDB}} for [[hexadecimal]]s. By default, integer literals default to {{rust|i32}} as its type. Suffixes such as {{rust|4u32}} can be used to explicitly set the type of a literal.{{sfn|Klabnik|Nichols|2023|pp=36-38}} Byte literals such as {{rust|b'X'}} are available to represent the [[ASCII]] value (as a {{rust|u8}}) of a specific character.{{sfn|Klabnik|Nichols|2023|p=502}}

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<syntaxhighlight lang="rust">

let tuple: (u32, i64bool) = (3, -3true);

let array: [i8; 5] = [1, 2, 3, 4, 5];

let tuple:value (bool,= bool)tuple.1; =// (true, true);

let value = tuple.1; // -3

let value = array[2]; // 3

</syntaxhighlight>

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<!-- todo str, and ! -->

=== Ownership and references ===

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</syntaxhighlight>

The function {{coderust|print_string}} takes ownership over the {{rust|String}} value passed in; Alternatively, {{coderust|&}} can be used to indicate a [[Reference (computer science)|reference]] type (in {{coderust|&String}}) and to create a reference (in {{coderust|&s}}):{{sfn|Klabnik|Nichols|2023|pp=71–72}}

<syntaxhighlight lang="rust">

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Because of these ownership rules, Rust types are known as ''[[linear types|linear]]'' or ''affine'' types, meaning each value can be used exactly once. This enforces a form of [[software fault isolation]] as the owner of a value is solely responsible for its correctness and deallocation.<ref name="BeyondSafety">{{Cite book |last1=Balasubramanian |first1=Abhiram |last2=Baranowski |first2=Marek S. |last3=Burtsev |first3=Anton |last4=Panda |first4=Aurojit |last5=Rakamarić |first5=Zvonimir |last6=Ryzhyk |first6=Leonid |title=Proceedings of the 16th Workshop on Hot Topics in Operating Systems |chapter=System Programming in Rust |date=2017-05-07 |chapter-url=https://doi.org/10.1145/3102980.3103006 |series=HotOS '17 |___location=New York, NY, US |publisher=Association for Computing Machinery |pages=156–161 |doi=10.1145/3102980.3103006 |isbn=978-1-4503-5068-6 |s2cid=24100599 |access-date=June 1, 2022 |archive-date=June 11, 2022 |archive-url=https://web.archive.org/web/20220611034046/https://dl.acm.org/doi/10.1145/3102980.3103006 |url-status=live}}</ref>

When a value goes out of scope, it is ''dropped'' by running its [[Destructor (computer programming)|destructor]]. The destructor may be programmatically defined through implementing the {{coderust|Drop}} [[#Traits|trait]]. This helps manage resources such as file handles, network sockets, and [[Lock (computer science)|locks]], since when objects are dropped, the resources associated with them are closed or released automatically.{{sfn|Klabnik|Nichols|2023|pp=327-30}}

==== Lifetimes ====

[[Object lifetime]] refers to the period of time during which a reference is valid; that is, the time between the object creation and destruction.<ref>{{Cite web |title=Lifetimes |url=https://doc.rust-lang.org/rust-by-example/scope/lifetime.html |access-date=2024-10-29 |website=Rust by Example |archive-date=2024-11-16 |archive-url=https://web.archive.org/web/20241116192422/https://doc.rust-lang.org/rust-by-example/scope/lifetime.html |url-status=live }}</ref> These ''lifetimes'' are implicitly associated with all Rust reference types. While often inferred, they can also be indicated explicitly with named lifetime parameters (often denoted {{coderust|'a}}, {{coderust|'b}}, and so on).<ref>{{Cite web |title=Explicit annotation |url=https://doc.rust-lang.org/rust-by-example/scope/lifetime/explicit.html |access-date=2024-10-29 |website=Rust by Example}}</ref>

Lifetimes in Rust can be thought of as [[Scope (computer science)|lexically scoped]], meaning that the duration of an object lifetime is inferred from the set of locations in the source code (i.e., function, line, and column numbers) for which a variable is valid.{{sfn|Klabnik|Nichols|2019|p=194}} For example, a reference to a local variable has a lifetime corresponding to the block it is defined in:{{sfn|Klabnik|Nichols|2019|p=194}}

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</syntaxhighlight>

The borrow checker in the Rust compiler then enforces that references are only used in the locations of the source code where the associated lifetime is valid.{{sfn|Klabnik|Nichols|2019|pp=75,134}}<ref>{{Cite web |last=Shamrell-Harrington |first=Nell |date=2022-04-15 |title=The Rust Borrow Checker – a Deep Dive |url=https://www.infoq.com/presentations/rust-borrow-checker/ |access-date=2022-06-25 |website=InfoQ |language=en |archive-date=2022-06-25 |archive-url=https://web.archive.org/web/20220625140128/https://www.infoq.com/presentations/rust-borrow-checker/ |url-status=live }}</ref> In the example above, storing a reference to variable {{coderust|x}} in {{coderust|r}} is valid, as variable {{coderust|x}} has a longer lifetime ({{coderust|'a}}) than variable {{coderust|r}} ({{coderust|'b}}). However, when {{coderust|x}} has a shorter lifetime, the borrow checker would reject the program:

<syntaxhighlight lang="rust">

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</syntaxhighlight>

Since the lifetime of the referenced variable ({{coderust|'b}}) is shorter than the lifetime of the variable holding the reference ({{coderust|'a}}), the borrow checker errors, preventing {{coderust|x}} from being used from outside its scope.{{sfn|Klabnik|Nichols|2019|pp=194-195}}

Lifetimes can be indicated using explicit ''lifetime parameters'' on function arguments. For example, the following code specifies that the reference returned by the function has the same lifetime as {{coderust|original}} (and ''not'' necessarily the same lifetime as {{coderust|prefix}}):{{sfn|Klabnik|Nichols|2023|pp=208–12}}

<syntaxhighlight lang="rust">

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==== Standard library ====

[[File:Rust standard libraries.svg|thumb|A diagram of the dependencies between the standard library modules of Rust.]]

The Rust [[standard library]] defines and implements many widely used custom data types, including core data structures such as {{coderust|Vec}}, {{coderust|Option}}, and {{coderust|HashMap}}, as well as [[smart pointer]] types. Rust also provides a way to exclude most of the standard library using the attribute {{rust|#![no_std]}};, this enablesfor applications, such as embedded devices, which want to remove dependency code or provide their own core data structures. Internally, the standard library is divided into three parts, {{coderust|core}}, {{coderust|alloc}}, and {{coderust|std}}, where {{coderust|std}} and {{Coderust|alloc}} are excluded by {{rust|#![no_std]}}.{{sfn|Gjengset|2021|pp=213-215}}

Rust uses [[Option type|<code>Option</code>]] to define optional values, which can be matched using <code>if let</code> or <code>match</code> to access the inner value:{{sfn|Klabnik|Nichols|2023|pp=108-110,113-114,116-117}}

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=== Polymorphism ===

Rust supports [[bounded parametric polymorphism]] through [[Trait (computer programming)|traits]] and [[generic function]]s.{{sfn|Klabnik|Nichols|2023|p=378}} Common behavior between types may be declared using traits and {{rust|impl}}s:{{sfn|Klabnik|Nichols|2023|pp=192-198}}

==== Generics ====

Rust's more advanced features include the use of [[generic function]]s. A generic function is given [[Generic programming|generic]] [[Parameter (computer programming)|parameters]], which allow the same function to be applied to different variable types. This capability reduces [[duplicate code]]{{sfn|Klabnik|Nichols|2019|pp=171–172}} and is known as [[parametric polymorphism]].

The following program calculates the sum of two things, for which addition is implemented using a generic function:

<syntaxhighlight lang="rust">

trait Zero: Sized {

use std::ops::Add;

fn zero() -> Self;

fn is_zero(&self) -> bool

where

Self: PartialEq,

{

self == &Zero::zero()

}

}

impl Zero for u32 {

// sum is a generic function with one type parameter, T

fn zero() -> u32 { 0 }

fn sum<T>(num1: T, num2: T) -> T

where

T: Add<Output = T>, // T must implement the Add trait where addition returns another T

{

num1 + num2 // num1 + num2 is syntactic sugar for num1.add(num2) provided by the Add trait

}

impl Zero for f32 {

fn main() {

letfn result1zero() =-> sum(10,Self 20);{ 0.0 }

println!("Sum is: {}", result1); // Sum is: 30

let result2 = sum(10.23, 20.45);

println!("Sum is: {}", result2); // Sum is: 30.68

}

</syntaxhighlight>

The example above also includes a method {{rust|is_zero}} which provides a default implementation that is not required when implementing the trait.{{sfn|Klabnik|Nichols|2023|pp=192-198}}

At compile time, polymorphic functions like <code>sum</code> are [[Instance (computer science)|instantiated]] with the specific types the code requires; in this case, sum of integers and sum of floats.

A function can then be made generic by adding type parameters inside angle brackets ({{rust|<Num>}}), which only allow types that implement the trait:

Generics can be used in functions to allow implementing a behavior for different types without repeating the same code. Generic functions can be written in relation to other generics, without knowing the actual type.{{sfn|Klabnik|Nichols|2019|pp=171–172,205}}

<syntaxhighlight lang="rust">

==== Traits ====

// sumzero is a generic function with one type parameter, TNum

[[File:UML class diagram Rust stdio.svg|thumb|Excerpt from {{Mono|std::io}}]]

fn zero<Num: Zero>() -> Num {

Rust's type system supports a mechanism called traits, inspired by [[type class]]es in the [[Haskell]] language,<ref name="influences"/> to define shared behavior between different types. For example, the <code>Add</code> trait can be implemented for floats and integers, which can be added; and the <code>Display</code> or <code>Debug</code> traits can be implemented for any type that can be converted to a string. Traits can be used to provide a set of common behavior for different types without knowing the actual type. This facility is known as [[ad hoc polymorphism]].

Num::zero()

}

fn main() {

Generic functions can constrain the generic type to implement a particular trait or traits; for example, an <code>add_one</code> function might require the type to implement <code>Add</code>. This means that a generic function can be type-checked as soon as it is defined. The implementation of 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 via the keyword <code>dyn</code> (short for dynamic).{{sfn|Klabnik|Nichols|2019|pp=181,182}} Because monomorphization duplicates the code for each type used, it can result in more optimized code for specific-use cases, but compile time and size of the output binary are also increased.{{sfn|Gjengset|2021|p=25}}

let a: u32 = zero();

let b: f32 = zero();

assert!(a.is_zero() && b.is_zero());

}

</syntaxhighlight>

In the examples above, {{rust|Num: Zero}} as well as {{rust|where Self: PartialEq}} are trait bounds that constrain the type to only allow types that implement {{rust|Zero}} or {{rust|PartialEq}}.{{sfn|Klabnik|Nichols|2023|pp=192-198}} Within a trait or impl, {{rust|Self}} refers to the type that the code is implementing.{{sfn|Klabnik|Nichols|2023|p=98}}

In addition to defining methods for a user-defined type, the <code>impl</code> keyword can be used to implement a trait for a type.{{sfn|Klabnik|Nichols|2019|pp=93}} Traits can provide additional derived methods when implemented.{{sfn|Klabnik|Nichols|2019|pp=182–184}} For example, the trait <code>Iterator</code> requires that the <code>next</code> method be defined for the type. Once the <code>next</code> method is defined, the trait can provide common functional helper methods over the iterator, such as <code>map</code> or <code>filter</code>.{{sfn|Klabnik|Nichols|2019|pp=281–283}}

Generics can be used in functions to allow implementing a behavior for different types without repeating the same code. Generic functions can be written in relation to other generics, without knowing the actual type.{{sfn|Klabnik|Nichols|2019|pp=171–172,205}}

==== Trait objects ====

RustGeneric traitsfunctions are implemented usinguse [[static dispatch]], meaning that the type of all valuesparameters isthat end up being used for the function must be known at compile time;. Generic functions generate separate copies of the code for each combination of generic parameters used in a process called [[monomorphization]].{{sfn|Klabnik|Nichols|2023|pp=191-192}} Because monomorphization duplicates the code for each type used, it is as performant as writing functions using concrete types,{{sfn|Klabnik|Nichols|2023|pp=191-192}} but compile time and size of the output binary could be howeverincreased.{{sfn|Gjengset|2021|p=25}}

However, Rust also uses a feature known as ''trait objects'' to accomplish [[dynamic dispatch]], a type of polymorphism where the implementation of a polymorphic operation is chosen at [[Runtime (program lifecycle phase)|runtime]]. This allows for behavior similar to [[duck typing]], where all data types that implement a given trait can be treated as functionally equivalent.{{sfn|Klabnik|Nichols|2023|loc=[https://doc.rust-lang.org/book/ch18-02-trait-objects.html 18.2. Using Trait Objects That Allow for Values of Different Types]}} Trait objects are declared using the syntax <code>dyn Tr</code> where <code>Tr</code> is a trait. Trait objects are dynamically sized, therefore they must be put behind a pointer, such as <code>Box</code>.{{sfn|Klabnik|Nichols|2019|pp=441–442}} The following example creates a list of objects where each object can be printed out using the <code>Display</code> trait:

<syntaxhighlight lang="Rust">

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=== Memory safety ===

Rust is designed to be [[memory safe]]. It does not permit null pointers, [[dangling pointer]]s, or [[data race]]s.<ref name="cnet">{{cite web |url=http://reviews.cnet.com/8301-3514_7-57577639/samsung-joins-mozillas-quest-for-rust/ |title=Samsung joins Mozilla's quest for Rust |last=Rosenblatt |first=Seth |date=2013-04-03 |publisher=[[CNET]] |access-date=2013-04-05 |archive-date=2013-04-04 |archive-url=https://web.archive.org/web/20130404142333/http://reviews.cnet.com/8301-3514_7-57577639/samsung-joins-mozillas-quest-for-rust/ |url-status=live}}</ref><ref name="lwn">{{cite web |last=Brown |first=Neil |date=2013-04-17 |title=A taste of Rust |url=https://lwn.net/Articles/547145/ |url-status=live |archive-url=https://web.archive.org/web/20130426010754/http://lwn.net/Articles/547145/ |archive-date=2013-04-26 |access-date=2013-04-25 |website=[[LWN.net]]}}</ref><ref name="The Rustonomicon">{{Cite web|url=https://doc.rust-lang.org/nomicon/races.html|title=Races|website=The Rustonomicon|access-date=2017-07-03|archive-date=2017-07-10|archive-url=https://web.archive.org/web/20170710194643/https://doc.rust-lang.org/nomicon/races.html|url-status=live}}</ref><ref name="Sensors">{{cite journal |last1=Vandervelden |first1=Thibaut |last2=De Smet |first2=Ruben |last3=Deac |first3=Diana |last4=Steenhaut |first4=Kris |last5=Braeken |first5=An |title=Overview of Embedded Rust Operating Systems and Frameworks |journal= Sensors|doi=10.3390/s24175818 |date=7 September 2024 |volume=24 |issue=17 |page=5818 |doi-access=free |pmid=39275729 |pmc=11398098 |bibcode=2024Senso..24.5818V }}</ref> Data values can be initialized only through a fixed set of forms, all of which require their inputs to be already initialized.<ref name="lang-faq">{{cite web |title=The Rust Language FAQ |publisher=The Rust Programming Language |url=http://static.rust-lang.org/doc/master/complement-lang-faq.html |url-status=dead |archive-url=https://web.archive.org/web/20150420104147/http://static.rust-lang.org/doc/master/complement-lang-faq.html |archive-date=2015-04-20 |year=2015 |access-date=2017-04-24}}</ref>

Unsafe code can subvert some of these restrictions, using the <code>unsafe</code> keyword.{{sfn|Klabnik|Nichols|2019|pp=418–427}} Unsafe code may also be used for low-level functionality, such as [[Volatile (computer programming)|volatile memory access]], architecture-specific intrinsics, [[type punning]], and inline assembly.{{sfn|McNamara|2021|p=139, 376–379, 395}}

=== Memory management ===

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The built-in reference types using the <code>&</code> symbol do not involve run-time reference counting. The safety and validity of the underlying pointers is verified at compile time, preventing [[dangling pointers]] and other forms of [[undefined behavior]].{{sfn|Klabnik|Nichols|2019|pp=70–75}} Rust's type system separates shared, [[Immutable object|immutable]] references of the form <code>&T</code> from unique, mutable references of the form <code>&mut T</code>. A mutable reference can be coerced to an immutable reference, but not vice versa.{{sfn|Klabnik|Nichols|2019|p=323}}

==== GenericsUnsafe ====

UnsafeRust's codememory cansafety subvertchecks may be circumvented through the someuse of these{{rust|unsafe}} restrictionsblocks. This allows programmers to deference arbitrary raw pointers, usingcall theexternal <code>unsafe</code>, or perform other low-level functionality not allowed by safe keywordRust.{{sfn|Klabnik|Nichols|20192023|pp=418–427420-429}} Unsafe code may also be used forSome low-level functionality, suchenabled in this way asincludes [[Volatile (computer programming)|volatile memory access]], architecture-specific intrinsics, [[type punning]], and inline assembly.{{sfn|McNamara|2021|p=139, 376–379, 395}}

Unsafe code is sometimes needed to implement complex data structures.<ref name="UnsafeRustUse">{{Cite journal |last1=Astrauskas |first1=Vytautas |last2=Matheja |first2=Christoph |last3=Poli |first3=Federico |last4=Müller |first4=Peter |last5=Summers |first5=Alexander J. |date=2020-11-13 |title=How do programmers use unsafe rust? |url=https://dl.acm.org/doi/10.1145/3428204 |journal=Proceedings of the ACM on Programming Languages |language=en |volume=4 |issue=OOPSLA |pages=1–27 |doi=10.1145/3428204 |issn=2475-1421|hdl=20.500.11850/465785 |hdl-access=free}}</ref> A frequently cited example is that it is difficult or impossible to implement [[doubly linked list]]s in safe Rust.<ref>{{Cite journal |last=Lattuada |first=Andrea |last2=Hance |first2=Travis |last3=Cho |first3=Chanhee |last4=Brun |first4=Matthias |last5=Subasinghe |first5=Isitha |last6=Zhou |first6=Yi |last7=Howell |first7=Jon |last8=Parno |first8=Bryan |last9=Hawblitzel |first9=Chris |date=2023-04-06 |title=Verus: Verifying Rust Programs using Linear Ghost Types |url=https://dl.acm.org/doi/10.1145/3586037 |journal=Software Artifact (virtual machine, pre-built distributions) for "Verus: Verifying Rust Programs using Linear Ghost Types" |volume=7 |issue=OOPSLA1 |pages=85:286–85:315 |doi=10.1145/3586037|hdl=20.500.11850/610518 |hdl-access=free }}</ref><ref>{{Cite journal |last=Milano |first=Mae |last2=Turcotti |first2=Julia |last3=Myers |first3=Andrew C. |date=2022-06-09 |title=A flexible type system for fearless concurrency |url=https://dl.acm.org/doi/10.1145/3519939.3523443 |journal=Proceedings of the 43rd ACM SIGPLAN International Conference on Programming Language Design and Implementation |series=PLDI 2022 |___location=New York, NY, USA |publisher=Association for Computing Machinery |pages=458–473 |doi=10.1145/3519939.3523443 |isbn=978-1-4503-9265-5|doi-access=free }}</ref><ref>{{Cite web |title=Introduction - Learning Rust With Entirely Too Many Linked Lists |url=https://rust-unofficial.github.io/too-many-lists/ |access-date=2025-08-06 |website=rust-unofficial.github.io}}</ref><ref>{{Cite journal |last=Noble |first=James |last2=Mackay |first2=Julian |last3=Wrigstad |first3=Tobias |date=2023-10-16 |title=Rusty Links in Local Chains✱ |url=https://doi.org/10.1145/3611096.3611097 |journal=Proceedings of the 24th ACM International Workshop on Formal Techniques for Java-like Programs |series=FTfJP '22 |___location=New York, NY, USA |publisher=Association for Computing Machinery |pages=1–3 |doi=10.1145/3611096.3611097 |isbn=979-8-4007-0784-1|url-access=subscription }}</ref>

Programmers using unsafe Rust are considered responsible for upholding Rust's memory and type safety requirements, for example, that no two mutable references exist pointing to the same ___location.<ref name=IsRustSafely>{{Cite journal |last=Evans |first=Ana Nora |last2=Campbell |first2=Bradford |last3=Soffa |first3=Mary Lou |date=2020-10-01 |title=Is rust used safely by software developers? |url=https://doi.org/10.1145/3377811.3380413 |journal=Proceedings of the ACM/IEEE 42nd International Conference on Software Engineering |series=ICSE '20 |___location=New York, NY, USA |publisher=Association for Computing Machinery |pages=246–257 |doi=10.1145/3377811.3380413 |isbn=978-1-4503-7121-6|arxiv=2007.00752 }}</ref> If programmers write code which violates these requirements, this results in [[undefined behavior]].<ref name=IsRustSafely/> The Rust documentation includes a list of behavior considered undefined, including accessing dangling or misaligned pointers, or breaking the aliasing rules for references.<ref>{{Cite web |title=Behavior considered undefined - The Rust Reference |url=https://doc.rust-lang.org/reference/behavior-considered-undefined.html |access-date=2025-08-06 |website=doc.rust-lang.org}}</ref>

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</syntaxhighlight>

The {{rust|#[repr(C)]}} attribute enables deterministic memory layouts for {{rust|struct}}s and {{rust|enum}}s for use across FFI boundaries.{{sfn|Gjengset|2021|pp=193-209}} External libraries such as {{coderust|bindgen}} and {{coderust|cxx}} can generate Rust bindings for C/C++.{{sfn|Gjengset|2021|pp=193-209}}<ref>{{Cite web|title=Safe Interoperability between Rust and C++ with CXX|url=https://www.infoq.com/news/2020/12/cpp-rust-interop-cxx/|date=2020-12-06|access-date=2021-01-03|website=InfoQ|language=en|archive-date=January 22, 2021|archive-url=https://web.archive.org/web/20210122142035/https://www.infoq.com/news/2020/12/cpp-rust-interop-cxx/|url-status=live}}</ref>

== Ecosystem ==

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Following Rust 1.0, new features are developed in ''nightly'' versions which are released daily. During each six-week release cycle, changes to nightly versions are released to beta, while changes from the previous beta version are released to a new stable version.<ref name="Rust Book G">{{harvnb|Klabnik|Nichols|2019|loc=Appendix G – How Rust is Made and "Nightly Rust"}}</ref>

Every two or three years, a new "edition" is produced. Editions are released to allow making limited [[breaking changes]], such as promoting {{coderust|await}} to a keyword to support [[async/await]] features. Crates targeting different editions can interoperate with each other, so a crate can upgrade to a new edition even if its callers or its dependencies still target older editions. Migration to a new edition can be assisted with automated tooling.{{sfn|Blandy|Orendorff|Tindall|2021|pp=176–177}}

=== IDE support ===

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== Performance ==

Since it performs no garbage collection, Rust is often faster than other memory-safe languages.<ref>{{Cite web |last1=Anderson |first1=Tim |date=2021-11-30 |title=Can Rust save the planet? Why, and why not |url=https://www.theregister.com/2021/11/30/aws_reinvent_rust/ |access-date=2022-07-11 |website=[[The Register]] |language=en |archiveurl-datestatus=2022-07-11live |archive-url=https://web.archive.org/web/20220711001629/https://www.theregister.com/2021/11/30/aws_reinvent_rust/ |urlarchive-statusdate=live2022-07-11}}</ref><ref name="BeyondSafety"/><ref>{{Cite web |last1=Yegulalp |first1=Serdar |date=2021-10-06 |title=What is the Rust language? Safe, fast, and easy software development |url=https://www.infoworld.com/article/3218074/what-is-rust-safe-fast-and-easy-software-development.html |access-date=2022-06-25 |website=[[InfoWorld]] |language=en |archiveurl-datestatus=2022-06-24live |archive-url=https://web.archive.org/web/20220624101013/https://www.infoworld.com/article/3218074/what-is-rust-safe-fast-and-easy-software-development.html |urlarchive-statusdate=live2022-06-24}}</ref> Most of Rust's memory safety guarantees impose no runtime overhead,{{sfn|McNamara|2021|p=11}} with the exception of [[Array (data structure)|array indexing]] which is checked at runtime by default.<ref name=SaferAtAnySpeed>{{Cite journal |last1=Popescu |first1=Natalie |last2=Xu |first2=Ziyang |last3=Apostolakis |first3=Sotiris |last4=August |first4=David I. |last5=Levy |first5=Amit |date=2021-10-15 |title=Safer at any speed: automatic context-aware safety enhancement for Rust |journal=Proceedings of the ACM on Programming Languages |volume=5 |issue=OOPSLA |quote="We observe a large variance in the overheads of checked indexing: 23.6% of benchmarks do report significant performance hits from checked indexing, but 64.5% report little-to-no impact and, surprisingly, 11.8% report improved performance ... Ultimately, while unchecked indexing can improve performance, most of the time it does not." |quote-page=5 |at=Section 2 |doi=10.1145/3485480 |s2cid=238212612|doi-access=free}}</ref> PerformanceThe performance impact of array indexing bounds checks varies, but can be significant in some cases.<ref name=SaferAtAnySpeed/>

Rust provides two "modes": safe and unsafe. Safe mode is the "normal" one, in which most Rust is written. In unsafe mode, the developer is responsible for the code's memory safety, which is used by developers for cases where the compiler is too restrictive.<ref name="UnsafeRustUse">{{Cite journal |last1=Astrauskas |first1=Vytautas |last2=Matheja |first2=Christoph |last3=Poli |first3=Federico |last4=Müller |first4=Peter |last5=Summers |first5=Alexander J. |date=2020-11-13 |title=How do programmers use unsafe rust? |url=https://dl.acm.org/doi/10.1145/3428204 |journal=Proceedings of the ACM on Programming Languages |language=en |volume=4 |issue=OOPSLA |pages=1–27 |doi=10.1145/3428204 |issn=2475-1421|hdl=20.500.11850/465785 |hdl-access=free}}</ref>

Many of Rust's features are so-called ''zero-cost abstractions'', meaning they are optimized away at compile time and incur no runtime penalty.{{sfn|McNamara|2021|p=19, 27}} The ownership and borrowing system permits [[zero-copy]] implementations for some performance-sensitive tasks, such as [[parsing]].<ref>{{Cite book |last=Couprie |first=Geoffroy |title=2015 IEEE Security and Privacy Workshops |chapter=Nom, A Byte oriented, streaming, Zero copy, Parser Combinators Library in Rust |date=2015 |pages=142–148 |doi=10.1109/SPW.2015.31 |isbn=978-1-4799-9933-0 |s2cid=16608844 }}</ref> [[Static dispatch]] is used by default to eliminate [[method call]]s, except for methods called on dynamic trait objects.{{sfn|McNamara|2021|p=20}} The compiler also uses [[inline expansion]] to eliminate [[function call]]s and statically-dispatched method invocations.<ref>{{Cite web |title=Code generation |url=https://doc.rust-lang.org/reference/attributes/codegen.html |access-date=2022-10-09 |website=The Rust Reference |archive-date=2022-10-09 |archive-url=https://web.archive.org/web/20221009202615/https://doc.rust-lang.org/reference/attributes/codegen.html |url-status=live}}</ref>

Since Rust uses [[LLVM]], all performance improvements in LLVM apply to Rust also.<ref name="how-fast-is-rust">{{cite web |url=https://doc.rust-lang.org/1.0.0/complement-lang-faq.html#how-fast-is-rust? |title=How Fast Is Rust? |website=The Rust Programming Language FAQ |access-date=11 April 2019 |archive-date=28 October 2020 |archive-url=https://web.archive.org/web/20201028102013/https://doc.rust-lang.org/1.0.0/complement-lang-faq.html#how-fast-is-rust? |url-status=live}}</ref> Unlike C and C++, Rust allows for reordering struct and enum elements<ref>{{Cite book |last1=Farshin |first1=Alireza |last2=Barbette |first2=Tom |last3=Roozbeh |first3=Amir |last4=Maguire |first4=Gerald Q. Jr |last5=Kostić |first5=Dejan |year=2021 |url=https://dlnext.acm.org/doi/abs/10.1145/3445814.3446724 |access-date=2022-07-12 |language=en |doi=10.1145/3445814.3446724 |quote=... While some compilers (e.g., Rust) support structure reordering [82], C & C++ compilers are forbidden to reorder data structures (e.g., struct or class) [74] ... |title=Proceedings of the 26th ACM International Conference on Architectural Support for Programming Languages and Operating Systems |chapter=PacketMill: Toward per-Core 100-GBPS networking |pages=1–17 |isbn=9781450383172 |s2cid=231949599 |archiveurl-datestatus=2022-07-12live |archive-url=https://web.archive.org/web/20220712060927/https://dlnext.acm.org/doi/abs/10.1145/3445814.3446724 |urlarchive-statusdate=live2022-07-12 |quote=... While some compilers (e.g., Rust) support structure reordering [82], C & C++ compilers are forbidden to reorder data structures (e.g., struct or class) [74] ... }}</ref> to reduce the sizes of structures in memory, for better memory alignment and efficiency.{{sfn|Gjengset|2021|p=22}}

== Adoption ==

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[[Discord]], an [[instant messaging]] software company, rewrote parts of its system in Rust for increased performance in 2020. In the same year, Dropbox announced that its [[file synchronization]] had been rewritten in Rust. [[Facebook]] ([[Meta Platforms|Meta]]) used Rust to redesign its system that manages source code for internal projects.<ref name="MITTechReview" />

In the 20242025 [[Stack Overflow]] Developer Survey, 1214.68% of respondents had recently done extensive development in Rust.<ref name="SO-20242025-survey">{{Cite web |title=20242025 Stack Overflow Developer Survey – Technology |url=https://survey.stackoverflow.co/20242025/technology |access-date=20242025-1108-2809 |website=[[Stack Overflow]]}}</ref> The survey named Rust the "most admired programming language" annually from 2016 to 20242025 (inclusive), as measured by the number of existing developers interested in continuing to work in the language.<ref>{{Cite web |last=Claburn |first=Thomas |date=2022-06-23 |title=Linus Torvalds says Rust is coming to the Linux kernel |url=https://www.theregister.com/2022/06/23/linus_torvalds_rust_linux_kernel/ |access-date=2022-07-15 |website=[[The Register]] |language=en |archive-date=2022-07-28 |archive-url=https://web.archive.org/web/20220728221531/https://www.theregister.com/2022/06/23/linus_torvalds_rust_linux_kernel/ |url-status=live }}</ref>{{refn|group=note|That is, among respondents who have done "extensive development work [with Rust] in over the past year" (1214.68%), Rust had the largest percentage who also expressed interest to "work in [Rust] over the next year" (8272.24%).<ref name="SO-20242025-survey"/>}} In 20242025, 2829.72% of developers not currently working in Rust expressed an interest in doing so.<ref name="SO-20242025-survey" />

[[DARPA]] has a project TRACTOR (Translating All C to Rust) automatically translating C to Rust using techniques such as static analysis, dynamic analysis, and large language models.<ref>{{cite web |last1=Wallach |first1=Dan |title=TRACTOR: Translating All C to Rust |url=https://www.darpa.mil/research/programs/translating-all-c-to-rust |publisher=[[DARPA]] |access-date=3 August 2025}}</ref>

== In academic research ==

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Rust's safety and performance have been investigated in [[programming language theory]] research.<ref>{{Cite journal |last1=Jung |first1=Ralf |last2=Jourdan |first2=Jacques-Henri |last3=Krebbers |first3=Robbert |last4=Dreyer |first4=Derek |date=2017-12-27 |title=RustBelt: securing the foundations of the Rust programming language |url=https://dl.acm.org/doi/10.1145/3158154 |journal=Proceedings of the ACM on Programming Languages |language=en |volume=2 |issue=POPL |pages=1–34 |doi=10.1145/3158154 |issn=2475-1421|hdl=21.11116/0000-0003-34C6-3 |hdl-access=free }}</ref><ref name="UnsafeRustUse"/><ref>{{Cite journal |last1=Popescu |first1=Natalie |last2=Xu |first2=Ziyang |last3=Apostolakis |first3=Sotiris |last4=August |first4=David I. |last5=Levy |first5=Amit |date=2021-10-20 |title=Safer at any speed: automatic context-aware safety enhancement for Rust |journal=Proceedings of the ACM on Programming Languages |language=en |volume=5 |issue=OOPSLA |pages=1–23 |doi=10.1145/3485480 |issn=2475-1421|doi-access=free }}</ref>

Rust's applicability to writing research software has been examined in other fields. A journal article published to ''[[Proceedings of the International Astronomical Union]]'' used Rust to simulate multi-planet systems.<ref name=ResearchSoftware1>{{Cite journal |last1=Blanco-Cuaresma |first1=Sergi |last2=Bolmont |first2=Emeline |date=2017-05-30 |title=What can the programming language Rust do for astrophysics? |url=https://www.cambridge.org/core/journals/proceedings-of-the-international-astronomical-union/article/what-can-the-programming-language-rust-do-for-astrophysics/B51B6DF72B7641F2352C05A502F3D881 |journal=[[Proceedings of the International Astronomical Union]] |language=en |volume=12 |issue=S325 |pages=341–344 |doi=10.1017/S1743921316013168 |arxiv=1702.02951 |bibcode=2017IAUS..325..341B |s2cid=7857871 |issn=1743-9213 |archive-date=2022-06-25 |access-date=2022-06-25 |archive-url=https://web.archive.org/web/20220625140128/https://www.cambridge.org/core/journals/proceedings-of-the-international-astronomical-union/article/what-can-the-programming-language-rust-do-for-astrophysics/B51B6DF72B7641F2352C05A502F3D881 |url-status=live }}</ref> An article published in ''[[Nature (journal)|Nature]]'' shared stories of bioinformaticians using Rust.<ref name="Nature"/> Both articles found that Rust has advantages for its performance and safety, and cited the [[learning curve]] as being a primary drawback to its adoption.<ref name=ResearchSoftware1/><ref name="Nature"/>

== Community ==