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Rust Programming Language Cheatsheet

A concise reference for the Rust programming language, covering syntax, data structures, control flow, and advanced features.

Basics & Syntax

Fundamental Syntax

Variable Declaration

let variable_name: type = value;

let mut mutable_variable = value;

Functions

 
fn function_name(parameter: type) -> return_type {
  // Function body
  return value;
}

Comments

// Single-line comment

/*
Multi-line
comment
*/

Printing to Console

println!("Hello, world!");
println!("Value: {}", variable);

Semicolons

Statements end with a semicolon ;. Expressions that return a value do not need a semicolon at the end. Omitting the semicolon implicitly returns the last expression in a block.

Modules

 
mod my_module {
  // Module content
}

use my_module::my_function;

Data Types

Scalar Types:

  • i32, i64 - Signed integers
  • u32, u64 - Unsigned integers
  • f32, f64 - Floating-point numbers
  • bool - Boolean type (true or false)
  • char - Character type (Unicode scalar values)

Compound Types:

  • Tuples: (i32, bool, f64)
  • Arrays: [i32; 5] (fixed size)
  • Slices: dynamically sized views into a contiguous sequence

String Types:

  • String: growable, owned, UTF-8 encoded string.
  • &str: string slice, a view into a String.

Ownership and Borrowing

Rust’s ownership system prevents memory errors.

Ownership Rules:

  1. Each value has a variable that’s its owner.
  2. There can only be one owner at a time.
  3. When the owner goes out of scope, the value is dropped.

Borrowing:
Creating references to data without taking ownership.

  • &: immutable reference (multiple allowed)
  • &mut: mutable reference (only one allowed at a time)

Lifetimes:
Annotated to ensure references are valid. Compiler infers most lifetimes.

Control Flow & Data Structures

Control Flow

If/Else

 
if condition {
  // Block of code
} else if other_condition {
  // Another block
} else {
  // Final block
}

Loops

 
loop {
  // Infinite loop, use 'break' to exit
  if condition { break; }
}

while condition {
  // While loop
}

for element in collection {
  // For loop
}

Match

 
match variable {
  pattern1 => { /* Code */ },
  pattern2 => { /* Code */ },
  _ => { /* Default case */ },
}

Data Structures

Structs:

struct Person {
  name: String,
  age: u32,
}

let person = Person { name: String::from("Alice"), age: 30 };

Enums:

enum Color {
  Red,
  Green,
  Blue,
}

let color = Color::Red;

Vectors:
Dynamically sized arrays.

let mut vector: Vec<i32> = Vec::new();
vector.push(1);
vector.push(2);

Hash Maps:

use std::collections::HashMap;

let mut map: HashMap<String, i32> = HashMap::new();
map.insert(String::from("key"), 10);

Error Handling

Result<T, E>: Represents either success (Ok(T)) or failure (Err(E)).

fn fallible_function() -> Result<i32, String> {
  if condition {
    Ok(value)
  } else {
    Err(String::from("Error message"))
  }
}

panic!: Unrecoverable error that terminates the program.

? operator: Propagates errors.

fn another_function() -> Result<i32, String> {
  let result = fallible_function()?;
  Ok(result + 1)
}

Advanced Features

Traits

Similar to interfaces in other languages. Define shared behavior.

trait Summary {
  fn summarize(&self) -> String;
}

struct NewsArticle {
  headline: String,
  author: String,
}

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

Trait Bounds: Specify that a generic type must implement a certain trait.

fn notify<T: Summary>(item: &T) { ... }

Generics

Generic Functions

 
fn largest<T: PartialOrd + Copy>(list: &[T]) -> T {
    let mut largest = list[0];

    for &item in list {
        if item > largest {
            largest = item;
        }
    }

    largest
}

Generic Structs

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

let integer = Point { x: 5, y: 10 };
let float = Point { x: 1.0, y: 4.0 };

Closures

Anonymous functions that can capture their environment.

let add_one = |x: i32| x + 1;

println!("{}", add_one(5)); // Prints 6

Capturing variables:

  • By reference: &T
  • By mutable reference: &mut T
  • By value: T (move semantics)

Concurrency

Threads:

use std::thread;

thread::spawn(|| {
  // Code to run in the new thread
});

Channels:
For message passing between threads.

use std::sync::mpsc;

let (tx, rx) = mpsc::channel();

thread::spawn(move || {
  tx.send(10).unwrap();
});

let received = rx.recv().unwrap();
println!("Got: {}", received);

Mutexes:
For protecting shared data.

use std::sync::{Mutex, Arc};

let counter = Arc::new(Mutex::new(0));
let mut handles = vec![];

for _ in 0..10 {
  let counter = Arc::clone(&counter);
  let handle = thread::spawn(move || {
    let mut num = counter.lock().unwrap();
    *num += 1;
  });
  handles.push(handle);
}

for handle in handles {
  handle.join().unwrap();
}

println!("Result: {}", *counter.lock().unwrap());

Cargo & Crates

Cargo Commands

  • cargo new project_name - Create a new project.
  • cargo build - Build the current project.
  • cargo run - Build and run the project.
  • cargo check - Check the project for errors without building.
  • cargo test - Run tests.
  • cargo doc - Build documentation.
  • cargo publish - Publish the crate to crates.io.

Cargo.toml

The manifest file for Rust projects. Specifies dependencies, metadata, etc.

[package]
name = "my_project"
version = "0.1.0"
edition = "2021"

[dependencies]
rand = "0.8.0"

Crates

Packages of Rust code.

  • crates.io: The official Rust package registry.
  • Import crates using extern crate crate_name; (Rust 2015) or use crate_name; (Rust 2018+).

Common Crates:

  • rand: Random number generation.
  • serde: Serialization and deserialization.
  • tokio: Asynchronous runtime.
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