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{{Short description|General-purpose programming language}}{{Good article}}{{Use American English|date=July 2022}}{{Use mdy dates|date=July 2022|cs1-dates=y}}

Primitive data type>Primitive Types!Type!Description!Examples

factoids
name	Rust| logo = Rust programming language black logo.svg| logo alt = Rust logo; a capital letter R set into a sprocket	Rust Foundation	property	reference	P348{edih}		Affine| inferred| nominal| static| strong| {edih}| programming language = Rust	Cross-platform software>Cross-platform{{refn	Including build tools, host tools, and standard library support for x86-64, ARM architecture family	, MIPS architecture>MIPS, RISC-V, WebAssembly, P6 (microarchitecture)	, AArch64, PowerPC, and Linux on IBM Z>s390x.PLATFORM SUPPORT >WEBSITE=THE RUSTC BOOK	ACCESS-DATE=2022-06-27, }}	Cross-platform software>Cross-platform{{refn	Including Windows, Linux, macOS, FreeBSD, NetBSD, and Illumos. Host build tools on Android (operating system)	, iOS, Haiku (operating system)>Haiku, Redox (operating system)	, and Fuchsia (operating system)>Fuchsia are not officially shipped; these operating systems are supported as targets.}}	MIT License>MIT and Apache License	{{refn>group=note	LLVM or MSVC, are subject to their own licenses.THE RUST PROGRAMMING LANGUAGE	PUBLISHER=THE RUST PROGRAMMING LANGUAGE, 19 October 2022, }}| file ext = .rs, .rlib	Alef| C#| C++| Cyclone| ElmWEB, Uniqueness Types,weblink 2016-10-08, Rust Blog, "Those of you familiar with the Elm style may recognize that the updated {{mono, --explain, messages draw heavy inspiration from the Elm approach."}}| Erlang| Haskell| Limbo| Newsqueak| OCaml| Ruby| Scheme| Standard ML| Swift }}	IdrisWEB, Uniqueness Types,weblink 2022-07-14, Idris 1.3.3 documentation, "They are inspired by ... ownership types and borrowed pointers in the Rust programming language.", | Project Verona| Spark| Swift| VWEB, V documentation (Introduction),weblink 2023-11-04, GitHub, en, | ZigWEB, Yegulalp, Serdar, 2016-08-29, New challenger joins Rust to topple C language,weblink 2022-10-19, InfoWorld, en, | }}}}Rust is a multi-paradigm, general-purpose programming language that emphasizes performance, type safety, and concurrency. It enforces memory safety—meaning that all references point to valid memory—without a garbage collector. To simultaneously enforce memory safety and prevent data races, its "borrow checker" tracks the object lifetime of all references in a program during compilation.Rust was influenced by ideas from functional programming, including immutability, higher-order functions, and algebraic data types. It is popular for systems programming.BOOK, Eshwarla, Prabhu,weblink Practical System Programming for Rust Developers: Build fast and secure software for Linux/Unix systems with the help of practical examples, 2020-12-24, Packt Publishing Ltd, 978-1-80056-201-1, en, BOOK, Blandy, Jim,weblink Programming Rust: Fast, Safe Systems Development, Orendorff, Jason, 2017-11-21, O'Reilly Media, Inc., 978-1-4919-2725-0, en, JOURNAL, Blanco-Cuaresma, Sergi, Bolmont, Emeline, 2017-05-30, What can the programming language Rust do for astrophysics?,weblink Proceedings of the International Astronomical Union, en, 12, S325, 341–344, 10.1017/S1743921316013168, 1702.02951, 2017IAUS..325..341B, 7857871, 1743-9213, Software developer Graydon Hoare created Rust as a personal project while working at Mozilla Research in 2006. Mozilla officially sponsored the project in 2009. In the years following the first stable release in May 2015, Rust was adopted by companies including Amazon, Discord, Dropbox, Google (Alphabet), Meta, and Microsoft. In December 2022, it became the first language other than C and assembly to be supported in the development of the Linux kernel.Rust has been noted for its rapid adoption,JOURNAL, Perkel, Jeffrey M., 2020-12-01, Why scientists are turning to Rust,weblink Nature (journal), Nature, en, 588, 7836, 185–186, 10.1038/d41586-020-03382-2, 33262490, 2020Natur.588..185P, 227251258, May 15, 2022, May 6, 2022,weblink live, and has been studied in programming language theory research.WEB, Computer Scientist proves safety claims of the programming language Rust,weblink 2022-05-15, EurekAlert!, en, February 24, 2022,weblink live, JOURNAL, Jung, Ralf, Jourdan, Jacques-Henri, Krebbers, Robbert, Dreyer, Derek, 2017-12-27, RustBelt: securing the foundations of the Rust programming language, Proceedings of the ACM on Programming Languages, 2, POPL, 66:1–66:34, 10.1145/3158154, 215791659, free, 21.11116/0000-0003-34C6-3, free, THESIS, Jung, Ralf, 2020, Understanding and evolving the Rust programming language,weblink en, 10.22028/D291-31946, May 15, 2022, March 8, 2022,weblink live, PhD, Saarland University, History File:MozillaCaliforniaHeadquarters.JPG|thumb|right|Mozilla Foundation headquarters in Mountain View, CaliforniaMountain View, California Origins (2006–2012) Rust began as a personal project in 2006 by Mozilla Research employee Graydon Hoare.WEB,weblink How Rust went from a side project to the world's most-loved programming language, Thompson, Clive, 2023-02-14, MIT Technology Review, en, 2023-02-23, Mozilla began sponsoring the project in 2009 as a part of the ongoing development of an experimental browser engine called Servo,WEB, Avram, Abel, 2012-08-03, Interview on Rust, a Systems Programming Language Developed by Mozilla,weblink live,weblink" title="web.archive.org/web/20130724045852weblink">weblink 2013-07-24, 2013-08-17, InfoQ, which was officially announced by Mozilla in 2010.WEB, Asay, Matt, 2021-04-12, Rust, not Firefox, is Mozilla's greatest industry contribution,weblink 2022-07-07, TechRepublic, en-US, CONFERENCE, Hoare, Graydon, Project Servo, Mozilla Annual Summit 2010, 7 July 2010, Whistler, Canada,weblink 22 February 2017, 11 July 2017,weblink" title="web.archive.org/web/20170711131514weblink">weblink live, Rust's memory and ownership system was influenced by region-based memory management in languages such as Cyclone and ML Kit.Around the same time, work shifted from the initial compiler written in OCaml to a self-hosting compiler based on LLVM written in Rust. The new Rust compiler successfully compiled itself in 2011.{{Better source needed|date=March 2024}} In the fall of 2011, the Rust logo was developed based on a bicycle chainring.WEB, Rust logo,weblink bugzilla.mozilla.org, 2 February 2024, Evolution (2012–2020) Rust's type system underwent significant changes between versions 0.2, 0.3, and 0.4. In version 0.2, which was released in March 2012, classes were introduced for the first time.WEB, Hoare, Graydon, 2012-03-29, [rust-dev] Rust 0.2 released,weblink 2024-04-04, 2022-11-06,weblink mail.mozilla.org, Four months later, version 0.3 added destructors and polymorphism, through the use of interfaces.WEB, Hoare, Graydon, 2012-07-12, [rust-dev] Rust 0.3 released,weblink 2022-06-12, mail.mozilla.org, 2022-08-24,weblink dead, In October 2012, version 0.4 was released, which added traits as a means of inheritance. Interfaces were combined with traits and removed as a separate feature; and classes were replaced by a combination of implementations and structured types.WEB, Hoare, Graydon, [rust-dev] Rust 0.4 released,weblink live,weblink October 31, 2021, 2021-10-31, mail.mozilla.org, October 15, 2012, Through the early 2010s, memory management through the ownership system was gradually consolidated to prevent memory bugs. By 2013, Rust's garbage collector was removed, with the ownership rules in place.In January 2014, the editor-in-chief of Dr. Dobb's Journal, Andrew Binstock, commented on Rust's chances of becoming a competitor to C++, along with D, Go, and Nim (then Nimrod). According to Binstock, while Rust was "widely viewed as a remarkably elegant language", adoption slowed because it radically changed from version to version.NEWS, Binstock, Andrew, January 7, 2014, The Rise And Fall of Languages in 2013, Dr. Dobb's Journal,weblink live,weblink" title="web.archive.org/web/20160807075745weblink">weblink 2016-08-07, 2022-11-20, The first stable release, Rust 1.0, was released on May 15, 2015.WEB, Version History, GitHub,weblink 2017-01-01, 2015-05-15,weblink live, WEB,weblink Announcing Rust 1.0, Rust Blog, The Rust Core Team, May 15, 2015, 2015-12-11, 2015-05-15,weblink" title="web.archive.org/web/20150515171337weblink">weblink live, The development of the Servo browser engine continued alongside Rust's own growth. In September 2017, Firefox 57 was released as the first version that incorporated components from Servo, in a project named "Firefox Quantum".WEB, Lardinois, Frederic, 2017-09-29, It's time to give Firefox another chance,weblink 2023-08-15, TechCrunch, en-US, Mozilla layoffs and Rust Foundation (2020–present) In August 2020, Mozilla laid off 250 of its 1,000 employees worldwide, as part of a corporate restructuring caused by the COVID-19 pandemic.WEB,weblink Mozilla lays off 250 employees while it refocuses on commercial products, Cimpanu, Catalin, ZDNet, 2020-12-02, 2020-08-11, March 18, 2022,weblink live, WEB,weblink Mozilla lays off 250 employees due to the pandemic, Engadget, Cooper, Daniel, 2020-12-02, 2020-08-11, 2020-12-13,weblink live, The team behind Servo was disbanded. The event raised concerns about the future of Rust, as some members of the team were active contributors to Rust.WEB, Tung, Liam, Programming language Rust: Mozilla job cuts have hit us badly but here's how we'll survive,weblink 2022-04-21, ZDNet, en, April 21, 2022,weblink live, 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 to take ownership of all trademarks and domain names, and take financial responsibility for their costs.WEB,weblink Laying the foundation for Rust's future, Rust Blog, 2020-12-02, 2020-08-18, 2020-12-02,weblink live, On February 8, 2021, the formation of the Rust Foundation was announced by its five founding companies (AWS, Huawei, Google, Microsoft, and Mozilla).WEB, 2020-02-08, Hello World!,weblink 2022-06-04, Rust Foundation, en, April 19, 2022,weblink live, WEB, 2021-02-09, Mozilla Welcomes the Rust Foundation, Mozilla Blog,weblinkweblink 2021-02-08, 2021-02-09, live, In a blog post published on April 6, 2021, Google announced support for Rust within the Android Open Source Project as an alternative to C/C++.WEB, Amadeo, Ron, 2021-04-07, Google is now writing low-level Android code in Rust,weblink 2021-04-08, Ars Technica, en-us, 2021-04-08,weblink live, On November 22, 2021, the Moderation Team, which was responsible for enforcing community standards and the Code of Conduct, announced their resignation "in protest of the Core Team placing themselves unaccountable to anyone but themselves".WEB, Tim, Anderson, Entire Rust moderation team resigns,weblink 2021-11-23, 2022-08-04, The Register, en, In May 2022, the Rust Core Team, other lead programmers, and certain members of the Rust Foundation board implemented governance reforms in response to the incident.WEB, Governance Update,weblink 2022-10-27, Inside Rust Blog, en, The Rust Foundation posted a draft for a new trademark policy on April 6, 2023, revising its rules on how the Rust logo and name can be used, which resulted in negative reactions from Rust users and contributors.WEB, Claburn, Thomas, Rust Foundation apologizes for trademark policy confusion, 2023-04-17,weblink 2023-05-07, The Register, en, Syntax and features Rust's syntax is similar to that of C and C++,WEB, Proven, Liam, 2019-11-27, Rebecca Rumbul named new CEO of The Rust Foundation,weblink 2022-07-14, The Register, en, "Both are curly bracket languages, with C-like syntax that makes them unintimidating for C programmers.", although many of its features were influenced by functional programming languages.{{sfn|Klabnik|Nichols|2019|p=263}} Hoare described Rust as targeted at "frustrated C++ developers" and emphasized features such as safety, control of memory layout, and concurrency. Safety in Rust includes the guarantees of memory safety, type safety, and lack of data races. Hello World program Below is a "Hello, World!" program in Rust. The {{Rust|fn}} keyword denotes a function, and the println! macro prints the message to standard output.{{sfn|Klabnik|Nichols|2019|pp=5–6}} Statements in Rust are separated by semicolons.fn main() { println!("Hello, World!"); } Keywords and control flow In Rust, blocks of code are delimited by curly brackets, and control flow is implemented by keywords including if, else, while, and for.{{sfn|Klabnik|Nichols|2019|pp=49–57}} Pattern matching can be done using the {{Rust|match}} keyword.{{sfn|Klabnik|Nichols|2019|pp=104–109}} In the examples below, explanations are given in comments, which start with {{code|//}}.{{sfn|Klabnik|Nichols|2019|p=49}}fn main() { // Defining a mutable variable with 'let mut' // Using the macro vec! to create a vector let mut values = vec![1, 2, 3, 4]; for value in &values { println!("value = {}", value); } if values.len() > 5 { println!("List is longer than five items"); } // Pattern matching match values.len() { 0 => println!("Empty"), 1 => println!("One value"), // pattern matching can use ranges of integers 2..=10 => println!("Between two and ten values"), 11 => println!("Eleven values"), // A `_` pattern is called a "wildcard", it matches any value _ => println!("Many values"), }; // while loop with predicate and pattern matching using let while let Some(value) = values.pop() { println!("value = {value}"); // using curly brackets to format a local variable } } Expression blocks Rust is expression-oriented, with nearly every part of a function body being an expression, including control-flow operators.{{sfn|Klabnik|Nichols|2019|pp=50–53}} The ordinary if expression is used instead of (?:|C's ternary conditional). With returns being implicit, a function does not need to end with a return expression; if the semicolon is omitted, the value of the last expression in the function is used as the return value,WEB, Tyson, Matthew, 2022-03-03, Rust programming for Java developers,weblink 2022-07-14, InfoWorld, en, as seen in the following recursive implementation of the factorial function:fn factorial(i: u64) -> u64 { if i == 0 { 1 } else { i * factorial(i - 1) } }The following iterative implementation uses the ..= operator to create an inclusive range:fn factorial(i: u64) -> u64 { (2..=i).product() } Closures {{excerpt|Anonymous function|Rust|subsections=yes}} Types Rust is strongly typed and statically typed. 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. Variables are declared with the keyword let, and type inference is used to determine their type.{{sfn|Klabnik|Nichols|2019|pp=24}} Variables assigned multiple times must be marked with the keyword mut (short for mutable).{{sfn|Klabnik|Nichols|2019|pp=32–33}}The default integer type is {{rust|i32}}, and the default floating point type is {{rust|f64}}. If the type of a literal number is not explicitly provided, either it is inferred from the context or the default type is used.{{sfn|Klabnik|Nichols|2019|pp=36–38}} Primitive types {| class"wikitable"
bool}}|Boolean value	{{rust|true{edih} {{rust|false}} }}
u8}}|Unsigned 8-bit integer (a byte)	{{rust|255u8{edih}This literal uses an explicit suffix, which is not needed when type can be inferred from the context {{Rust|b'W'}} (ASCII encoded byte) }}
{{rust|i8{edih} {{rust|i16}} {{rust|i32}} {{rust|i64}} {{rust|i128}} }}	Signed integers, up to 128-bit computing>128 bits	{{rust|7{edih}Interpreted as {{rust|i32}} by default, or inferred from the context {{rust|7i128}} }}
{{rust|u16{edih} {{rust|u32}} {{rust|u64}} {{rust|u128}} }}	Unsigned integers, up to 128-bit computing>128 bits	{{rust|14{edih}Type inferred from the context {{rust|14u128}} }}
{{rust|usize{edih} {{rust|isize}} }}	Pointer (computer programming)>Pointer-sized integers (size depends on platform)	{{rust|14usize{edih} {{rust|-2isize}} }}
{{rust|f32{edih} {{rust|f64}} }}	Floating-point arithmetic>Floating-point numbers	{{rust|-3f32{edih} }}
char}}	UTF-32 scalar value (occupies 4 bytes) A Unicode codepoint that is not a surrogate{{sfn|Klabnik|Nichols|2019|pp=39–40{edih} }}	{{Rust|'a'{edih} {{Rust|'语'}} {{Rust|'🦀'}} (Emoji) {{Rust|'u{200D}'}} (Unicode escape, zero-width joiner) }}
str}}	UTF-8-encoded string slice, the primitive string type. It is usually seen in its borrowed form, {{Rust>&str}}. It is also the type of string literals, {{Rust		ACCESS-DATE=2023-06-23, doc.rust-lang.org,	{{Rust|"Hello"{edih} {{Rust|"3"}} {{Rust|"🦀🦀🦀"}} }}
[T; N]}}	Array (data structure)>Array – collection of N objects of the same type T, stored in contiguous memory	{{Rust|[2, 4, 6]{edih} {{Rust|[0; 100]}} {{Rust|b"Hello"}} }}
[T]}}		ACCESS-DATE=2023-06-23, doc.rust-lang.org,	{{Rust|[1, 2, 3, 4, 5][..i]}} {{Rust|"Hello, world!".as_bytes()}} {{Rust|let v {{=}} vec![1, 2, 3]; v.as_slice()}} }}
{{Rust|(T, U, ..)}}}}|Tuple – a finite heterogeneous sequence	{{Rust|(){edih} (An empty tuple, the unit type in Rust) {{Rust|(5,)}} ({{Rust|(5)}} is parsed as an integer)WEB, Tuples,weblink 2023-10-01, Rust By Example, {{Rust|("Age", 10)}} {{Rust|(1, true, "Name")}} }}
!}}	Bottom type>Never type (unreachable value)	let x {{=}} { return 123 };}}

Standard library {| class"wikitable"|+Summary of Rust's types in the standard library

!Type!Description!ExamplesString}}|UTF-8-encoded strings (dynamic)

• {{Rust|String::new(){edih}
• {{Rust|String::from("Hello")}}
• {{Rust|"🦀🦀🦀".to_string()}}

• {{Rust|OsStr{edih}
• {{Rust|OsString}}

UTF-16 strings without an internal 0 byte. Unlike these, {{Rust>str}} and {{RustACCESS-DATE=2023-10-02 ACCESS-DATE=2023-10-02, doc.rust-lang.org, )

• {{Rust|OsStr::new("Hello"){edih}
• {{Rust|OsString::from("world")}}

• {{Rust|Path{edih}
• {{Rust|PathBuf}}

Path (computing)>Paths (borrowedPATH IN STD::PATH – RUST >URL=HTTPS://DOC.RUST-LANG.ORG/BETA/STD/PATH/STRUCT.PATH.HTML WEBSITE=DOC.RUST-LANG.ORG, and dynamicPATHBUF IN STD::PATH – RUST >URL=HTTPS://DOC.RUST-LANG.ORG/BETA/STD/PATH/STRUCT.PATHBUF.HTML WEBSITE=DOC.RUST-LANG.ORG, )

• {{Rust|Path::new("./path/to")}}
• {{Rust|PathBuf::from(r"C:.pathto")}}

• {{Rust|CStr{edih}
• {{Rust|CString}}

C (programming language)>C-compatible, null-terminated strings (borrowedSTD::BOXED – RUST >URL=HTTPS://DOC.RUST-LANG.ORG/STD/BOXED/INDEX.HTML WEBSITE=DOC.RUST-LANG.ORG, and dynamic)

• {{Rust|c"Hello"{edih}
• {{Rust|CStr::from_bytes_with_nul(b"Hello").unwrap()}}
• {{Rust|CString::new("world").unwrap()}}

Vec}}|Dynamic arrays

• {{Rust|Vec::new(){edih}
• {{Rust|vec![1, 2, 3, 4, 5]}}

Option}}|Option type

• {{Rust|None{edih}
• {{Rust|Some(3)}}
• {{Rust|Some("hello")}}

Result}}Exception handling>Error handling using a result type

• {{Rust|Ok(3){edih}
• {{Rust|Err("something went wrong")}}

Box}}Heap (programming)>heap-allocated value.STD::BOXED – RUST >URL=HTTPS://DOC.RUST-LANG.ORG/STD/BOXED/INDEX.HTML WEBSITE=DOC.RUST-LANG.ORG, Similar to C++'s std::unique_ptr.| let boxed: Box = Box::new(5);let val: u8 = *boxed;Rc}}Reference counting pointerRC IN STD::RC – RUST ACCESS-DATE=2023-06-24, doc.rust-lang.org, |let five = Rc::new(5);let also_five = five.clone();Arc}}Linearizability>Atomic, Thread safety reference counting pointerARC IN STD::SYNC – RUST ACCESS-DATE=2023-06-24, doc.rust-lang.org, |let foo = Arc::new(vec![1.0, 2.0]);let a = foo.clone(); // a can be sent to another threadCell}}ACCESS-DATE=2023-06-24, doc.rust-lang.org, |let c = Cell::new(5);c.set(10);|MutexLock (computer science)>mutex lock for shared data contained within.MUTEX IN STD::SYNC – RUST >URL=HTTPS://DOC.RUST-LANG.ORG/BETA/STD/SYNC/STRUCT.MUTEX.HTML WEBSITE=DOC.RUST-LANG.ORG, |let mutex = Mutex::new(0_u32);let _guard = mutex.lock();RwLock}}Readers–writer lockRWLOCK IN STD::SYNC – RUST ACCESS-DATE=2023-06-24, doc.rust-lang.org, |let lock = RwLock::new(5);let r1 = lock.read().unwrap();Condvar}}Monitor (synchronization)>conditional monitor for shared dataCONDVAR IN STD::SYNC – RUST >URL=HTTPS://DOC.RUST-LANG.ORG/BETA/STD/SYNC/STRUCT.CONDVAR.HTML WEBSITE=DOC.RUST-LANG.ORG, | // As long as the value inside the `Mutex` is `true`, we wait.let _guard = cvar.wait_while(lock.lock().unwrap(), |pending| { *pending }).unwrap();Duration}}ACCESS-DATE=2023-06-24, doc.rust-lang.org, |Duration::from_millis(1) // 1ms1=HashMap}}Hash tableHASHMAP IN STD::COLLECTIONS – RUST ACCESS-DATE=2023-06-24, doc.rust-lang.org, |let mut player_stats = HashMap::new();player_stats.insert("damage", 1);player_stats.entry("health").or_insert(100);1=BTreeMap}}B-treeBTREEMAP IN STD::COLLECTIONS – RUST ACCESS-DATE=2023-06-24, doc.rust-lang.org, |let mut solar_distance = BTreeMap::from([ ]);solar_distance.entry("Earth").or_insert(1.0);Option values are handled using syntactic sugar, such as the if let construction, to access the inner value (in this case, a string):{{sfn|McNamara|2021}}fn main() {

}

Pointers {| class"wikitable"Pointer (computer programming)>pointer and reference primitive types

!Type!Description!Examples

• {{Rust|&T{edih}
• {{Rust|&mut T}}

Reference (computer science)>References (immutable and mutable)

• {{Rust|let x_ref {{={edih} {{not a typo|&x;}}}}
• {{Rust|let x_ref {{=}} &mut x;}}

• {{Rust|Option{edih}
• {{Rust|Option}}

• Option wrapped reference
• Possibly null reference

• {{Rust|None{edih}
• {{Rust|let x_ref {{=}} Some(&x);}}
• {{Rust|let x_ref {{=}} Some(&mut x);}}

* {{Rust|Box}}

• {{Rust|Option}}}}|A pointer to heap-allocated value

(or possibly null pointer if wrapped in option)* {{Rust|let boxed {{=}} Box::new(0);}}

• {{Rust|let boxed {{=}} Some(Box::new("Hello World"));}}}}

• {{Rust|const T{edih}
• {{Rust|mut T}}

• Raw pointers (immutable and mutable)
• Possibly null; {{Rust|unsafe{edih} to dereference

• {{Rust|let x_ptr {{={edih} &x as const T;}}
• {{Rust|let x_ptr {{=}} &mut x as mut T;}}

Rust does not use null pointers to indicate a lack of data, as doing so can lead to null dereferencing. Accordingly, the basic & and &mut references are guaranteed to not be null. Rust instead uses Option for this purpose: Some(T) indicates that a value is present, and None is analogous to the null pointer.{{sfn|Klabnik|Nichols|2019|pp=101–104}} Option implements a "null pointer optimization", avoiding any spatial overhead for types that cannot have a null value (references or the NonZero types, for example).WEB, std::option - Rust,weblink 2023-11-12, doc.rust-lang.org, Unlike references, the raw pointer types *const and *mut may be null; however, it is impossible to dereference them unless the code is explicitly declared unsafe through the use of an unsafe block. Unlike dereferencing, the creation of raw pointers is allowed inside of safe Rust code.{{sfn|Klabnik|Nichols|2019|pp=418–427}}

User-defined types

User-defined types are created with the struct or enum keywords. The struct keyword is used to denote a record type that groups multiple related values.{{sfn|Klabnik|Nichols|2019|p=83}} enums can take on different variants at runtime, with its capabilities similar to algebraic data types found in functional programming languages.{{sfn|Klabnik|Nichols|2019|p=97}} Both structs and enums can contain fields with different types.{{sfn|Klabnik|Nichols|2019|pp=98–101}} Alternative names for the same type can be defined with the type keyword.{{sfn|Klabnik|Nichols|2019|pp=438–440}}The impl keyword can define methods for a user-defined type. Data and functions are defined separately. Implementations fulfill a role similar to that of classes within other languages.{{sfn|Klabnik|Nichols|2019|pp=93}}

Type conversion

{{excerpt|Type conversion|Rust}}

Ownership and lifetimes

Rust's ownership system consists of rules that ensure memory safety without using a garbage collector. At compile time, each value must be attached to a variable called the owner of that value, and every value must have exactly one owner.{{sfn|Klabnik|Nichols|2019|pp=59–61}} Values are moved between different owners through assignment or passing a value as a function parameter. Values can also be borrowed, meaning they are temporarily passed to a different function before being returned to the owner.{{sfn|Klabnik|Nichols|2019|pp=63–68}} With these rules, Rust can prevent the creation and use of dangling pointers:{{sfn|Klabnik|Nichols|2019|pp=63–68}}{{sfn|Klabnik|Nichols|2019|pp=74–75}}fn print_string(s: String) { }fn main() { }Because of these ownership rules, Rust types are known as 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.BOOK, Balasubramanian, Abhiram, Baranowski, Marek S., Burtsev, Anton, Panda, Aurojit, Rakamarić, Zvonimir, Ryzhyk, Leonid, Proceedings of the 16th Workshop on Hot Topics in Operating Systems, System Programming in Rust, 2017-05-07,weblink HotOS '17, New York, NY, US, Association for Computing Machinery, 156–161, 10.1145/3102980.3103006, 978-1-4503-5068-6, 24100599, June 1, 2022, June 11, 2022,weblink live, When a value goes out of scope, it is dropped by running its destructor. The destructor may be programmatically defined through implementing the {{code|Drop}} trait. This helps manage resources such as file handles, network sockets, and locks, since when objects are dropped, the resources associated with them are closed or released automatically.{{sfn|Klabnik|Nichols|2023|pp=327-30}}Lifetimes are usually an implicit part of all reference types in Rust. Each lifetime encompasses a set of locations in the code for which a variable is valid. 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}}fn main() { } // ------------------+The borrow checker in the Rust compiler uses lifetimes to ensure that the values a reference points to remain valid.{{sfn|Klabnik|Nichols|2019|pp=75,134}}WEB, Shamrell-Harrington, Nell, The Rust Borrow Checker – a Deep Dive,weblink 2022-06-25, InfoQ, en, In the example above, storing a reference to variable {{code|x}} to {{code|r}} is valid, as variable {{code|x}} has a longer lifetime ({{code|'a}}) than variable {{code|r}} ({{code|'b}}). However, when {{code|x}} has a shorter lifetime, the borrow checker would reject the program:fn main() { } // ------------------+Since the lifetime of the referenced variable ({{code|'b}}) is shorter than the lifetime of the variable holding the reference ({{code|'a}}), the borrow checker errors, preventing {{code|x}} from being used from outside its scope.{{sfn|Klabnik|Nichols|2019|pp=194-195}}Rust defines the relationship between the lifetimes of the objects created and used by functions, using lifetime parameters, as a signature feature.{{sfn|Klabnik|Nichols|2019|pp=192–204}}The example below parses some configuration options from a string and creates a struct containing the options. The struct only contains references to the data; so, for the struct to remain valid, the data referred to by the struct must be valid as well. The function signature for parse_config specifies this relationship explicitly. In this example, the explicit lifetimes are unnecessary in newer Rust versions, due to lifetime elision, which is an algorithm that automatically assigns lifetimes to functions if they are trivial.{{sfn|Klabnik|Nichols|2019|pp=201–203}}use std::collections::HashMap;// This struct has one lifetime parameter, 'src. The name is only used within the struct's definition.

1. [derive(Debug)]

struct Config Config