---
website: https://www.rust-lang.org
source: https://doc.rust-lang.org/book
obj: application
---

# Rust
[Rust](https://www.rust-lang.org/) is a statically-typed programming language known for its emphasis on performance, safety, and concurrency. Originally developed by [Mozilla](../../../internet/websites/clearnet/Mozilla.md), Rust has gained popularity for its ability to provide low-level control over system resources without sacrificing memory safety. Rust uses [Cargo](../../../applications/development/cargo.md) as its package manager and build tool.

## Syntax
Your application starts within the main function, so the simplest application is this:
```rust
fn main() {

}
```

### Variables
You can declare variables. Variables are immutable by default, if you need to change them you have to use the `mut` keyword. Every variable is strongly typed, but you can either ommit type information and let the compiler infer the type or explicitly state it. Constants which never change can be made as well.

```rust
let var = "Hello";
let mut mutable = "World";
let explicit_num: isize = 0;
const NINE_K: isize = 9000;
```

### Data Types & Ownership
Every variable in Rust is strongly typed. You can define your own types and use the compiler together with an algebraic type system to your advantage.
  
In Rust, primitive types are classified into two categories: scalar types and compound types:

#### Scalar Types
1. **Integers:**
    - `i8`: Signed 8-bit integer
    - `i16`: Signed 16-bit integer
    - `i32`: Signed 32-bit integer
    - `i64`: Signed 64-bit integer
    - `i128`: Signed 128-bit integer
    - `u8`: Unsigned 8-bit integer
    - `u16`: Unsigned 16-bit integer
    - `u32`: Unsigned 32-bit integer
    - `u64`: Unsigned 64-bit integer
    - `u128`: Unsigned 128-bit integer
    - `isize`: Platform-dependent signed integer
    - `usize`: Platform-dependent unsigned integer
2. **Floating-point:**
    - `f32`: 32-bit floating-point number
    - `f64`: 64-bit floating-point number
3. **Characters:**
    - `char`: A [Unicode](../../../files/Unicode.md) character (4 bytes)
4. **Booleans:**
    - `bool`: Boolean type representing either `true` or `false`

#### Compound Types
1. **Arrays:**
    - `[T; N]`: Fixed-size array of elements of type `T` and length `N`
2. **Tuples:**
    - `(T1, T2, ..., Tn)`: Heterogeneous collection of elements of different types

#### Pointer Types
1. **References:**
    - `&T`: Immutable reference
    - `&mut T`: Mutable reference
2. **Raw Pointers:**
    - `*const T`: Raw immutable pointer
    - `*mut T`: Raw mutable pointer

Rust enforces some rules on variables in order to be memory safe. So there are three kinds of variables you could have:
- Owned Variable `T`: You are the owner of this variable with data type `T`
- Reference `&T`: You have a read only reference of the variables content
- Mutable Reference `&mut T`: You have a modifiable reference to the variable

> Note: If a function does not need to mutate or own a variable, consider using a reference

### Conditionals
Conditionals like `if` and `match` can be used, while `match` can do more powerful pattern matching than `if`.
```rust
let age = 20;
if age > 18 {
    println!("Adult");
} else if age == 18 {
    println!("Exactly 18");
} else {
    println!("Minor");
}

match age {
    18 => println!("Exactly 18"),
    _ => println!("Everything else")
}
```

### Loops
There are three types of loops.
```rust
loop {
    println!("Going on until time ends");
}

for item in list {
    println!("This is {item}");
}

while condition {
    println!("While loop");
}
```

### Functions
One can use functions with optional arguments and return types. If you `return` on the last line, you can ommit the `return` keyword and `;` to return the value.
```rust
fn printHello() {
    println!("Hello");
}

fn greet(name: &str) {
    println!("Hello {name}");
}

fn add_two(a: isize) -> isize {
    a + 2 // same as "return a + 2;"
}
```

### Enums
Rust has enums which can even hold some data.
```rust
enum StatusCode {
    NOT_FOUND,
    OK,
    Err(String)
}

let err_response = StatusCode::Err(String::from("Internal Error"));

match err_response {
    StatusCode::Ok => println!("Everything is fine"),
    StatusCode::NOT_FOUND => println!("Not found");
    StatusCode::Err(err) => println!("Some error: {err}"); // will print "Some error: Internal Error"
}

// other way to pattern match for a single pattern
if let StatusCode::Err(msg) = err_response {
    println!("{msg}!");
}
```

### Structs
Rust has some object-oriented features like structs.
```rust
struct Person {
    first_name: String,
    age: isize
}

impl Person {
    fn new(first_name: &str) -> Self {
        Self {
            first_name: first_name.to_string(),
            age: 0
        }
    }

    fn greet(&self) {
        println!("Hello {}", self.first_name);
    }

	fn get_older(&mut self) {
		self.age += 1;
	}
}
```

### Comments
Rust has support for comments. There are regular comments, multiline comments and documentation comments. Documentation comments get used when generating documation via `cargo doc` and inside the IDE.
```rust
// This is a comment

/*
This
is multiline
comment
*/

/// This function does something.
/// Documentation comments can be styled with markdown as well.
/// 
/// # Example
///
/// If you place a rust code block here, you can provide examples on how to use this function and `cargo test` will automatically run this code block when testing.
fn do_something() {

}
```

### Modules
You can split your code up into multiple modules for better organization.
```rust
// will search for `mymod.rs` or `mymod/mod.rs` beside the source file and include it as `mymod`;
mod mymod;

// inline module
mod processor {
    struct AMD {
        name: String
    }
}

fn main() {
    // full syntax
    let proc = processor::AMD{ name: "Ryzen".to_string() };

    // you can put often used symbols in scope
    use processor::AMD;
    let proc = AMD{ name: "Ryzen".to_string() };
}
```

### Generics
Generics let you write code for multiple data types without repeating yourself. Instead of an explicit data type, you write your code around a generic type.

```rust
struct Point<T> {
    x: T,
    y: T,
}

impl<T> Point<T> {
    fn x(&self) -> &T {
        &self.x
    }
}

// you can declare methods which only work for specific data types.
impl Point<f32> {
    fn distance_from_origin(&self) -> f32 {
        (self.x.powi(2) + self.y.powi(2)).sqrt()
    }
}

impl<X1, Y1> Point<X1, Y1> {
    // define generic types on functions
    fn mixup<X2, Y2>(self, other: Point<X2, Y2>) -> Point<X1, Y2> {
        Point {
            x: self.x,
            y: other.y,
        }
    }
}

enum Option<T> {
    Some(T),
    None,
}

// you can have multiple generic types
enum Result<T, E> {
    Ok(T),
    Err(E),
}

```

### Traits
Traits let you define shared behavior on structs. You define what methods a struct should have and it is up the the struct to implement them.
```rust
pub trait Summary {
    fn summarize(&self) -> String;
}

// you can define default behaviour
pub trait DefaultSummary {
    fn summarize(&self) -> String {
        String::from("(Read more...)")
    }
}

pub struct NewsArticle {
    pub headline: String,
    pub location: String,
    pub author: String,
    pub content: String,
}

impl Summary for NewsArticle {
    fn summarize(&self) -> String {
        format!("{}, by {} ({})", self.headline, self.author, self.location)
    }
}

pub struct Tweet {
    pub username: String,
    pub content: String,
    pub reply: bool,
    pub retweet: bool,
}

impl Summary for Tweet {
    fn summarize(&self) -> String {
        format!("{}: {}", self.username, self.content)
    }
}

// use traits as parameters
pub fn notify(item: &impl Summary) {
    println!("Breaking news! {}", item.summarize());
}

// you can also restrict generic types to only ones that implement certain traits
pub fn notify<T: Summary>(item: &T) {
    println!("Breaking news! {}", item.summarize());
}

// even multiple at once
pub fn notify<T: Summary + Display>(item: &T) {}

// another way to restrict types to traits
fn some_function<T, U>(t: &T, u: &U) -> i32
where
    T: Display + Clone,
    U: Clone + Debug,
{}

// you can restrict at impl level too
struct Pair<T> {
    x: T,
    y: T,
}

impl<T> Pair<T> {
    fn new(x: T, y: T) -> Self {
        Self { x, y }
    }
}

impl<T: Display + PartialOrd> Pair<T> {
    // this function is only available if T has Display and PartialOrd
    fn cmp_display(&self) {
        if self.x >= self.y {
            println!("The largest member is x = {}", self.x);
        } else {
            println!("The largest member is y = {}", self.y);
        }
    }
}
```

Common traits you can implement on your types are:
- `Clone`: Allows creating a duplicate of an object.
```rust
pub trait Clone {
    fn clone(&self) -> Self;
}
```
- `Copy`: Types that can be copied by simple bitwise copying.
```rust
pub trait Copy: Clone {}
```
- `Debug`: Enables formatting a value for debugging purposes.
```rust
pub trait Debug {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>;
}
```
- `Default`: Provides a default value for a type.
```rust
pub trait Default {
    fn default() -> Self;
}
```
- `Eq` and `PartialEq`: Enables equality comparisons.
```rust
pub trait Eq: PartialEq<Self> {}

pub trait PartialEq<Rhs: ?Sized = Self> {
    fn eq(&self, other: &Rhs) -> bool;
}
```
- `Ord` and `PartialOrd`: Enables ordering comparisons.
```rust
pub trait Ord: Eq + PartialOrd<Self> {
    fn cmp(&self, other: &Self) -> Ordering;
}

pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
    fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
}
```
- `Iterator`: Represents a sequence of values.
```rust
pub trait Iterator {
    type Item;
    fn next(&mut self) -> Option<Self::Item>;
    // Other iterator methods...
}
```
- `Read` and `Write`: For reading from and writing to a byte stream.
```rust
pub trait Read {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error>;
}

pub trait Write {
    fn write(&mut self, buf: &[u8]) -> Result<usize, Error>;
}
```
- `Fn`, `FnMut`, and `FnOnce`: Traits for function types with different levels of mutability.
```rust
pub trait Fn<Args> {
    // function signature
}

pub trait FnMut<Args>: Fn<Args> {
    // function signature
}

pub trait FnOnce<Args>: FnMut<Args> {
    // function signature
}
```
- `Drop`: Specifies what happens when a value goes out of scope.
```rust
pub trait Drop {
    fn drop(&mut self);
}
```
- `Deref` and `DerefMut`: Used for overloading dereference operators.
```rust
pub trait Deref {
    type Target: ?Sized;
    fn deref(&self) -> &Self::Target;
}

pub trait DerefMut: Deref {
    fn deref_mut(&mut self) -> &mut Self::Target;
}
```
- `AsRef` and `AsMut`: Allows types to be used as references.
```rust
pub trait AsRef<T: ?Sized> {
    fn as_ref(&self) -> &T;
}

pub trait AsMut<T: ?Sized>: AsRef<T> {
    fn as_mut(&mut self) -> &mut T;
}
```
- `Index` and `IndexMut`: Enables indexing into a data structure.
```rust
pub trait Index<Idx: ?Sized> {
    type Output: ?Sized;
    fn index(&self, index: Idx) -> &Self::Output;
}

pub trait IndexMut<Idx: ?Sized>: Index<Idx> {
    fn index_mut(&mut self, index: Idx) -> &mut Self::Output;
}
```
- `Send` and `Sync`: Indicate whether a type is safe to be transferred between threads (Send) or shared between threads (Sync).
```rust
unsafe trait Send {}
unsafe trait Sync {}
```
- `Into` and `From`: Facilitates conversions between types.
```rust
pub trait Into<T> {
    fn into(self) -> T;
}

pub trait From<T> {
    fn from(T) -> Self;
}
```
- `Display`: Formatting values for user display.
```rust
pub trait Display {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>;
}
```
- `FromStr` and `ToString`: Enables conversion between strings and other types.
```rust
pub trait FromStr {
    type Err;
    fn from_str(s: &str) -> Result<Self, Self::Err>;
}

pub trait ToString {
    fn to_string(&self) -> String;
}
```
- `Error`: Represents errors that can occur during the execution of a program.
```rust
pub trait Error: Debug {
    fn source(&self) -> Option<&(dyn Error + 'static)>;
}
```
- `Add`, `Sub`, `Mul`, and `Div`: Traits for arithmetic operations.
```rust
pub trait Add<RHS = Self> {
    type Output;
    fn add(self, rhs: RHS) -> Self::Output;
}

// Similar traits for Sub, Mul, and Div
```

### Closures
Closures are anonymous functions. They can be assigned to variables, passed as parameters or returned from a function.

```rust
fn  add_one_v1   (x: u32) -> u32 { x + 1 }
let add_one_v2 = |x: u32| -> u32 { x + 1 };
let add_one_v3 = |x|             { x + 1 };
let add_one_v4 = |x|               x + 1  ;

// this function takes ownership over variables it uses as noted by `move`
thread::spawn(
    move || println!("From thread: {:?}", list)
    ).join().unwrap();

// To use closures as parameters, specify the type. It is one of the Fn traits
impl<T> Option<T> {
    pub fn unwrap_or_else<F>(self, f: F) -> T
    where
        F: FnOnce() -> T
    {
        match self {
            Some(x) => x,
            None => f(),
        }
    }
}
```

### Iterators
The [iterator pattern](../patterns/behavioral/Iterator%20Pattern.md) allows you to perform some task on a sequence of items in turn. An iterator is responsible for the logic of iterating over each item and determining when the sequence has finished. When you use iterators, you don’t have to reimplement that logic yourself.

```rust
let v1 = vec![1, 2, 3];
let v1_iter = v1.iter();
let v2: Vec<_> = v1.iter().map(|x| x + 1).collect();
```

With this you can do functional programming with the iterators.

Some functions on them include:
- `chain(other)`: An iterator that links two iterators together, in a chain.
- `cloned()`: An iterator that clones the elements of an underlying iterator.
- `copied()`: An iterator that copies the elements of an underlying iterator.
- `cycle()`: An iterator that repeats endlessly.
- `empty()`: An iterator that yields nothing.
- `enumerate()`: An iterator that yields the current count and the element during iteration.
- `filter(predicate)`: An iterator that filters the elements of `iter` with `predicate`.
- `filterMap(f)`: An iterator that uses `f` to both filter and map elements from `iter`.
- `flat_map(f)`: An iterator that maps each element to an iterator, and yields the elements of the produced iterators.
- `flatten()`: An iterator that flattens one level of nesting in an iterator of things that can be turned into iterators.
- `from_fn(f)`: An iterator where each iteration calls the provided closure `F: FnMut() -> Option<T>`.
- `fuse()`: An iterator that yields `None` forever after the underlying iterator yields `None` once.
- `inspect(f)`: An iterator that calls a function with a reference to each element before yielding it.
- `map(f)`: An iterator that maps the values of `iter` with `f`.
- `map_while(f)`: An iterator that only accepts elements while `predicate` returns `Some(_)`.
- `once(value)`: An iterator that yields an element exactly once.
- `peekable()`: An iterator with a `peek()` that returns an optional reference to the next element.
- `repeat(value)`: An iterator that repeats an element endlessly.
- `rev()`: A double-ended iterator with the direction inverted.
- `skip(n)`: An iterator that skips over `n` elements of `iter`.
- `skip_while(f)`: An iterator that rejects elements while `predicate` returns `true`.
- `step_by(n)`: An iterator for stepping iterators by a custom amount.
- `successors(first, f)`: A new iterator where each successive item is computed based on the preceding one.
- `take(n)`: An iterator that only iterates over the first `n` iterations of `iter`.
- `take_while(f)`: An iterator that only accepts elements while `predicate` returns `true`.
- `zip(a, b)`: An iterator that iterates two other iterators simultaneously.

### Standard Library
Rust, a systems programming language known for its focus on safety and performance, comes with a rich standard library that provides a wide range of modules to handle common tasks.

1. **`std::collections`**: Data structures like `Vec`, `HashMap`, etc.
2. **`std::fs`**: File system manipulation and I/O operations.
3. **`std::thread`**: Facilities for concurrent programming with threads.
4. **`std::time`**: Time-related types and functionality.
5. **`std::io`**: Input and output facilities.
6. **`std::path`**: Path manipulation utilities.
7. **`std::env`**: Interface to the environment, command-line arguments, etc.
9. **`std::string`**: String manipulation utilities.
10. **`std::cmp`**: Comparison traits and functions.
11. **`std::fmt`**: Formatting traits and utilities.
12. **`std::result`**: Result type and related functions.
13. **`std::error`**: Error handling utilities.
14. **`std::sync`**: Synchronization primitives.
15. **`std::net`**: Networking functionality.
16. **`std::num`**: Numeric types and operations.
17. **`std::char`**: Character manipulation utilities.
18. **`std::mem`**: Memory manipulation utilities.
19. **`std::slice`**: Slice manipulation operations.
20. **`std::marker`**: Marker traits for influencing Rust's type system.

## Macros
We’ve used macros like `println!` before, but we haven’t fully explored what a macro is and how it works. The term _macro_ refers to a family of features in Rust: _declarative_ macros with `macro_rules!` and three kinds of _procedural_ macros:
- Custom `#[derive]` macros that specify code added with the `derive` attribute used on structs and enums
- Attribute-like macros that define custom attributes usable on any item
- Function-like macros that look like function calls but operate on the tokens specified as their argument

Fundamentally, macros are a way of writing code that writes other code, which is known as _metaprogramming_. All of these macros _expand_ to produce more code than the code you’ve written manually.

Declarative macros work almost like a `match` statement.
```rust
macro_rules! mymacro {
	($expression:expr) => {
		println!("{}", $expression)
	};
	($expression:expr, $other:expr) => {
		println!("{} {}", $expression, $other)
	};
}

mymacro!("Hello World");
mymacro!("Hello", "World");
```

This macro gets expanded to the code inside the `macro_rules!` section with the provided arguments. For more information on macros, see the [docs](https://doc.rust-lang.org/reference/macros-by-example.html).

## [Crates](https://lib.rs/)
- [anyhow](https://lib.rs/crates/anyhow): Flexible concrete Error type built on `std::error::Error`
- [itertools](https://lib.rs/crates/itertools): Extra iterator adaptors, iterator methods, free functions, and macros
- [num_enum](https://lib.rs/crates/num_enum): Procedural macros to make inter-operation between primitives and enums easier

### Encoding
- [bincode](https://lib.rs/crates/bincode): A binary serialization / deserialization strategy for transforming structs into bytes and vice versa!
- [serde](https://lib.rs/crates/serde): A generic serialization/deserialization framework
- [serde_json](https://lib.rs/crates/serde_json): A [JSON](../../../files/JSON.md) serialization file format
- [serde_yaml](https://lib.rs/crates/serde_yaml): [YAML](../../../files/YAML.md) data format for Serde
- [bson](https://lib.rs/crates/bson): Encoding and decoding support for [BSON](../../../files/BSON.md) in Rust
- [hex](https://lib.rs/crates/hex): Encoding and decoding data into/from hexadecimal representation
- [toml](https://lib.rs/crates/toml): A native Rust encoder and decoder of [TOML](../../../files/TOML.md)-formatted files and streams.
- [base64](https://lib.rs/crates/base64): encodes and decodes [base64](../../../files/Base64.md) as bytes or utf8

### Algorithms
- [rand](https://lib.rs/crates/rand): Random number generators and other randomness functionality

### Debugging
- [log](https://lib.rs/crates/log): A lightweight logging facade for Rust
- [env_logger](https://lib.rs/crates/env_logger): A logging implementation for `log` which is configured via an environment variable

### Mail
- [lettre](https://lib.rs/crates/lettre): [Email](../../../internet/eMail.md) client

### Visualization
- [plotters](https://lib.rs/crates/plotters): A Rust drawing library focus on data plotting for both WASM and native applications
- [plotly](https://lib.rs/crates/plotly): A plotting library powered by Plotly.js
- [textplot](https://lib.rs/crates/textplots): Terminal plotting library

### Templates
- [maud](https://lib.rs/crates/maud): Compile-time [HTML](../../../internet/HTML.md) templates
- [tera](https://lib.rs/crates/tera): Template engine based on [Jinja](../../../tools/Jinja.md) templates

### Media
- [image](https://lib.rs/crates/image): Imaging library. Provides basic image processing and encoders/decoders for common image formats.

### CLI
- [rustyline](https://lib.rs/crates/rustyline): Rustyline, a readline implementation based on Antirez's Linenoise
- [clap](https://lib.rs/crates/clap): A simple to use, efficient, and full-featured Command Line Argument Parser
- [crossterm](https://lib.rs/crates/crossterm): A crossplatform terminal library for manipulating terminals
- [indicatif](https://lib.rs/crates/indicatif): A progress bar and cli reporting library for Rust
- [argh](https://lib.rs/crates/argh): Derive-based argument parser optimized for code size
- [owo-colors](https://lib.rs/crates/owo-colors): Zero-allocation terminal colors that'll make people go owo
- [yansi](https://lib.rs/crates/yansi): A dead simple ANSI terminal color painting library

### Compression
- [flate2](https://lib.rs/crates/flate2): DEFLATE compression and decompression exposed as Read/BufRead/Write streams. Supports miniz_oxide and multiple zlib implementations. Supports zlib, gzip, and raw deflate streams.
- [tar](https://lib.rs/crates/tar): A Rust implementation of a [TAR](../../../applications/cli/compression/tar.md) file reader and writer.
- [zstd](https://lib.rs/crates/zstd): Binding for the zstd compression library
- [unrar](https://lib.rs/crates/unrar): list and extract RAR archives

### Databases
- [rusqlite](https://lib.rs/crates/rusqlite): Ergonomic wrapper for [SQLite](../SQLite.md)
- [sqlx](https://lib.rs/crates/sqlx): The Rust [SQL](SQL.md) Toolkit. An async, pure Rust [SQL](SQL.md) crate featuring compile-time checked queries without a DSL. Supports PostgreSQL, MySQL, and [SQLite](../SQLite.md).
- [mongodb](https://lib.rs/crates/mongodb): The official [MongoDB](../../../applications/development/MongoDB.md) driver for Rust

### Data and Time
- [chrono](https://lib.rs/crates/chrono): Date and time library for Rust
- [humantime](https://lib.rs/crates/humantime): A parser and formatter for `std::time::{Duration, SystemTime}`

### HTTP
- [hyper](https://lib.rs/crates/hyper): A fast and correct [HTTP](../../../internet/HTTP.md) library
- [reqwest](https://lib.rs/crates/reqwest): higher level [HTTP](../../../internet/HTTP.md) client library
- [actix-web](https://lib.rs/crates/actix-web): Actix Web is a powerful, pragmatic, and extremely fast web framework for Rust

### Text
- [regex](https://lib.rs/crates/regex): An implementation of [regular expressions](../../../tools/Regex.md) for Rust. This implementation uses finite automata and guarantees linear time matching on all inputs.
- [comfy-table](https://lib.rs/crates/comfy-table): An easy to use library for building beautiful tables with automatic content wrapping
- [similar](https://lib.rs/crates/similar): A diff library for Rust

### Concurrency
- [parking_lot](https://lib.rs/crates/parking_lot): More compact and efficient implementations of the standard synchronization primitives
- [crossbeam](https://lib.rs/crates/crossbeam): Tools for concurrent programming
- [rayon](https://lib.rs/crates/rayon): Simple work-stealing parallelism for Rust

### Async
- [tokio](https://lib.rs/crates/tokio): An event-driven, non-blocking I/O platform for writing asynchronous I/O backed applications
- [futures](https://lib.rs/crates/futures): An implementation of futures and streams featuring zero allocations, composability, and iterator-like interfaces
