Rust language cheatcode

Basic Types & Variables

Boolean bool
Unsigned integers u8, u16, u32, u64, u128
Signed integers i8, i16, i32, i64, i128
Floating point numbers f32, f64
Platform specific integers
usize - Unsigned integer. Same number of bits as the platform's pointer type.
isize - Signed integer. Same number of bits as the platform's pointer type.
char - Unicode scalar value
&str - String slice
String - Owned string
Tuple

let coordinates = (82, 64);
let score = ("Team A", 12)

Array & Slice

// Arrays must have a known length and all elements must be initialized
let array = [1, 2, 3, 4, 5];
let array2 = [0; 3]; // [0, 0, 0]
 
// Unlike arrays the length of a slice is determined at runtime
let slice = &array[1 .. 3];

HashMap

use std::collections::HashMap;
 
let mut subs = HashMap::new();
subs.insert(String::from("LGR"), 100000);
// Insert key if it doesn't have a value
subs.entry("Golang Dojo".to_owned()) .or_insert(3);

Struct

// Definition
struct User {
	username: String,
	active: bool,
}
 
// Instantiation
let user1 = User {
	username: String::from("bogdan"),
	active: true,
};
 
// Tuple struct
struct Color(i32, i32, i32);
let black = Color(0, 0, 0);

Enum

// Definition
enum Command {
	Quit,
	Move { x: i32, y: i32 },
	Speak(String),
	ChangeBGColor(i32, i32, i32),
}
 
// Instantiation
let msg1 = Command::Quit;
let msg2 = Command::Move{ x: 1, y: 2 };
let msg3 = Command::Speak("Hi".to_owned());
let msg4 = Command::ChangeBGColor(0, 0, 0);

Constant

const MAX_POINTS: u32 = 100_000;

Static variable

// Unlike constants static variables are
// stored in a dedicated memory location
// and can be mutated.
static MAJOR_VERSION: u32 = 1;
static mut COUNTER: u32 = 0;

Mutability

let mut x = 5;
x = 6;

Shadowing

let x = 5;
let x = x * 2;

Type alias

// `NanoSecond` is a new name for `u64`.
type NanoSecond = u64;

Control Flow

if and if let

let num = Some(22);
if num.is_some() {
	println!("number is: {}", num.unwrap());
}
// match pattern and assign variable
	if let Some(i) = num { println!("number is: {}", i);
}

loop

let mut count = 0;
loop {
	count += 1;
	if count == 5 {
		break; // Exit loop }
}

Nested loops & labels

'outer: loop {
	'inner: loop {
	// This breaks the inner loop
		break;
		// This breaks the outer loop
	break 'outer;
	}
}

Returning from loops

let mut counter = 0;
 
let result = loop {
	counter += 1;
	if counter == 10 {
		break counter;
	}
};

while and while let

while n < 101 {
	n += 1;
}
 
let mut optional = Some(0);
 
while let Some(i) = optional {
	print!("{}", i);
}

for loop

for n in 1..101 {
	println!("{}", n);
}
 
let names = vec!["Bogdan", "Wallace"];
 
for name in names.iter() {
	println!("{}", name);
}

match

let optional = Some(0);
 
match optional {
	Some(i) => println!("{}", i),
	None => println!("No value.")
}

References, Ownership, and Borrowing

Ownership rules

Each value in Rust has a variable that’s called its owner.
There can only be one owner at a time.
When the owner goes out of scope, the value will be dropped.

Borrowing rules

At any given time, you can have either one mutable reference or any number of immutable references.
References must always be valid.

Creating references

let s1 = String::from("hello world!");
let s1_ref = &s1; // immutable reference
 
let mut s2 = String::from("hello");
let s2_ref = &mut s2; // mutable reference
 
s2_ref.push_str(" world!");

Copy, Move, and Clone

// Simple values which implement the Copy trait are copied by value
let x = 5;
let y = x;
 
println!("{}", x); // x is still valid
 
// The string is moved to s2 and s1 is invalidated
let s1 = String::from("Hi, mom!");
let s2 = s1; // Shallow copy a.k.a move
 
println!("{}", s1); // Error: s1 is invalid
 
let s1 = String::from("Hi, mom!");
let s2 = s1.clone(); // Deep copy
 
 
// Valid because s1 isn't moved
println!("{}", s1);

Ownership and functions

fn main() {
	let x = 5;
	takes_copy(x); // x is copied by value
 
	let s = String::from("Let’s Get Rusty!");
	// s is moved into the function
	takes_ownership(s);
 
	// return value is moved into s1
	let s1 = gives_ownership();
 
	let s2 = String::from("LGR");
	let s3 = takes_and_gives_back(s2);
}
 
fn takes_copy(some_integer: i32) {
	println!("{}", some_integer);
}
 
fn takes_ownership(some_string: String) {
	println!("{}", some_string);
} // some_string goes out of scope and drop is called. The backing memory is freed.
 
fn gives_ownership() -> String {
	let some_string = String::from("LGR");
	some_string
}
 
fn takes_and_gives_back(some_string: String) -> String {
	some_string
}

Pattern Matching

Basics

let x = 5;
 
match x {
	// matching literals
	1 => println!("one"),
	// matching multiple patterns
	2 | 3 => println!("two or three"),
	// matching ranges
	4..=9 => println!("within range"),
	// matching named variables
	x => println!("{}", x),
	// default case (ignores value)
	_ => println!("default Case")
}

Destructuring

struct Point {
	x: i32,
	y: i32,
}
 
let p = Point { x: 0, y: 7 };
 
match p {
	Point { x, y: 0 } => {
		println!("{}" , x);
	},
	Point { x, y } => {
		println!("{} {}" , x, y);
	},
}
 
enum Shape {
	Rectangle { width: i32, height: i32 },
	Circle(i32),
}
 
let shape = Shape::Circle(10);
 
match shape {
	Shape::Rectangle { x, y } => //...
	Shape::Circle(radius) => //...
}

Ignoring values

struct SemVer(i32, i32, i32);
 
let version = SemVer(1, 32, 2);
 
match version {
	SemVer(major, _, _) => {
		println!("{}", major);
	}
}
 
let numbers = (2, 4, 8, 16, 32);
 
match numbers {
	(first, .., last) => {
		println!("{}, {}", first, last);
	}
}

Match guards

let num = Some(4);
 
match num {
	Some(x) if x < 5 => println!("less than five: {}", x),
	Some(x) => println!("{}", x),
	None => (),
}

@ bindings

struct User {
	id: i32
}
 
let user = User { id: 5 };
 
match user {
	User {
		id: id_variable @ 3..=7,
	} => println!("id: {}", id_variable),
	User { id: 10..=12 } => {
		println!("within range");
	},
	User { id } => println!("id: {}", id),
}

Iterators

Usage

// Methods that consume iterators
let v1 = vec![1, 2, 3];
let v1_iter = v1.iter();
let total: i32 = v1_iter.sum();
 
// Methods that produce new iterators
let v1: Vec<i32> = vec![1, 2, 3];
let iter = v1.iter().map(|x| x + 1);
 
// Turning iterators into a collection
let v1: Vec<i32> = vec![1, 2, 3];
let v2: Vec<_> = v1.iter().map(|x| x + 1).collect();

Implementing the Iterator trait

struct Counter {
	count: u32,
}
 
impl Counter {
	fn new() -> Counter {
		Counter { count: 0 }
	}
}
 
impl Iterator for Counter {
	type Item = u32;
 
	fn next(&mut self) -> Option<Self::Item>
	{
		if self.count < 5 {
			self.count += 1;
			Some(self.count)
		} else {
			None
		}
	}
}

Error Handling

Throw unrecoverable error

panic!("Critical error! Exiting!");

Option enum

fn get_user_id(name: &str) -> Option<u32> {
	if database.user_exists(name) {
	return Some(database.get_id(name))
}
 
	None
}

Result enum

fn get_user(id: u32) -> Result<User, Error> {
	if is_logged_in_as(id) {
		return Ok(get_user_object(id))
	}
 
	Err(Error { msg: "not logged in" })
}

? operator

fn get_salary(db: Database, id: i32) -> Option<u32> {
	Some(db.get_user(id)?.get_job()?.salary)
}
 
fn connect(db: Database) -> Result<Connection, Error> {
	let conn = db.get_active_instance()?.connect()?;
	Ok(conn)
}

Combinators

.map

let some_string = Some("LGR".to_owned());
 
let some_len = some_string.map(|s| s.len());
 
struct Error { msg: String }
struct User { name: String }
 
let string_result: Result<String, Error> = Ok("Bogdan".to_owned());
 
let user_result: Result<User, Error> =
	string_result.map(|name| {
		User { name }
	});

.and_then

let vec = Some(vec![1, 2, 3]);
let first_element = vec.and_then(
	|vec| vec.into_iter().next()
);
 
let string_result: Result<&'static str, _> = Ok("5");
let number_result =
	string_result
	.and_then(|s| s.parse::<u32>());

Multiple error types

Define custom error type

type Result<T> = std::result::Result<T, CustomError>;
 
#[derive(Debug, Clone)]
struct CustomError;
 
impl fmt::Display for CustomError {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		write!(f, "custom error message")
	}
}

Boxing errors

use std::error;
 
type Result<T> = std::result::Result<T, Box<dyn error::Error>>;

Iterating over errors

Ignore failed items with filter_map()

let strings = vec!["LGR", "22", "7"];
let numbers: Vec<_> = strings
	.into_iter()
	.filter_map(|s| s.parse::<i32>().ok())
	.collect();

Fail the entire operation with collect()

let strings = vec!["LGR", "22", "7"];
 
let numbers: Result<Vec<_>, _> = strings
	.into_iter()
	.map(|s| s.parse::<i32>())
	.collect();

Collect all valid values and failures with partition()

let strings = vec!["LGR", "22", "7"];
 
let (numbers, errors): (Vec<_>, Vec<_>) = strings
	.into_iter()
	.map(|s| s.parse::<i32>())
	.partition(Result::is_ok);
 
let numbers: Vec<_> = numbers
	.into_iter()
	.map(Result::unwrap)
	.collect();
 
let errors: Vec<_> = errors
	.into_iter()
	.map(Result::unwrap_err)
	.collect();

Generics, Traits, and Lifetimes

Using generics

struct Point<T, U> {
	x: T,
	y: U,
}
 
impl<T, U> Point<T, U> {
	fn mixup<V, W>(self, other: Point<V, W>) -> Point<T, W> {
		Point {
			x: self.x,
			y: other.y,
		}
	}
}

Defining traits

trait Animal {
	fn new(name: &'static str) -> Self;
	fn noise(&self) -> &'static str { "" }
}
 
struct Dog { name: &'static str }
 
impl Dog {
	fn fetch() { // ... }
}
 
impl Animal for Dog {
	fn new(name: &'static str) -> Dog {
		Dog { name: name }
	}
 
fn noise(&self) -> &'static str {
		"woof!"
	}
}

Default implementations with Derive

// A tuple struct that can be printed
#[derive(Debug)]
struct Inches(i32);

Trait bounds

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

impl trait

fn make_adder_function(y: i32) -> impl Fn(i32) -> i32 {
	let closure = move |x: i32| { x + y };
	closure
}

Trait objects

pub struct Screen {
	pub components: Vec<Box<dyn Draw>>,
}

Operator overloading

use std::ops::Add;
 
#[derive(Debug, Copy, Clone, PartialEq)]
struct Point {
	x: i32,
	y: i32,
}
 
impl Add for Point {
	type Output = Point;
 
	fn add(self, other: Point) -> Point {
		Point {
			x: self.x + other.x,
			y: self.y + other.y,
		}
	}
}

Supertraits

use std::fmt;
 
trait Log: fmt::Display {
	fn log(&self) {
		let output = self.to_string();
		println!("Logging: {}", output);
	}
}

Lifetimes in function signatures

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
	if x.len() > y.len() {
		x
	} else {
		y
	}
}

Lifetimes in struct definitions

struct User<'a> {
full_name: &'a str,
}

Static lifetimes

let s: &'static str = "Hi, mom!";

Functions, Function Pointers & Closures

Associated functions and methods

struct Point { x: i32, y: i32, }
 
impl Point {
	// Associated function
	fn new(x: i32, y: i32) -> Point {
		Point { x: x, y: y }
	}
 
	// Method
	fn getX(&self) -> i32 { self.x }
}

Function pointers

fn do_twice(f: fn(i32) -> i32, arg: i32) -> i32 {
f(arg) + f(arg)
}

Creating closures

let add_one = |num: u32| -> u32 {
num + 1
};

Returning closures

fn add_one() -> impl Fn(i32) -> i32 {
	|x| x + 1
}
 
fn add_or_subtract(x: i32) -> Box<dyn Fn(i32) -> i32> {
	if x > 10 {
		Box::new(move |y| y + x)
	} else {
		Box::new(move |y| y - x)
	}
}

Closure traits

FnOnce - consumes the variables it captures from its enclosing scope.
FnMut - mutably borrows values from its enclosing scope.
Fn - immutably borrows values from its enclosing scope.

Store closure in struct

struct Cacher<T>
where
	T: Fn(u32) -> u32,
{
	calculation: T,
	value: Option<u32>,
}

Function that accepts closure or function pointer

fn do_twice<T>(f: T, x: i32) -> i32
	where T: Fn(i32) -> i32
{
	f(x) + f(x)
}

Pointers

References

let mut num = 5;
let r1 = &num; // immutable reference
let r2 = &mut num; // mutable reference

Raw pointers

let mut num = 5;
// immutable raw pointer
let r1 = &num as *const i32;
// mutable raw pointer
let r2 = &mut num as *mut i32;

Smart pointers

Box<T> - for allocating values on the heap

let b = Box::new(5);

Rc<T> - multiple ownership with reference counting

let a = Rc::new(5);
let b = Rc::clone(&a);

Ref<T>, RefMut<T>, and RefCell<T> - enforce borrowing rules at runtime instead of compile time.

let num = 5;
let r1 = RefCell::new(5);
// Ref - immutable borrow
let r2 = r1.borrow();
// RefMut - mutable borrow
let r3 = r1.borrow_mut();
// RefMut - second mutable borrow
let r4 = r1.borrow_mut();

Multiple owners of mutable data

let x = Rc::new(RefCell::new(5));

Packages, Crates, and Modules

Definitions

Packages - A Cargo feature that lets you build, test, and share crates.
Crates - A tree of modules that produces a library or executable.
Modules and use - Let you control the organization, scope, and privacy of paths.
Paths - A way of naming an item, such as a struct, function, or module.

Creating a new package with a binary crate

$ cargo new my-project

Creating a new package with a library crate

$ cargo new my-project --lib

Defining and using modules

fn some_function() {}
 
mod outer_module { // private module
	pub mod inner_module { // public module
		pub fn inner_public_function() {
			super::super::some_function();
		}
 
		fn inner_private_function() {}
	}
}
 
fn main() {
	// absolute path
	crate::outer_module::
	inner_module::inner_public_function();
 
	// relative path path
	outer_module::
	inner_module::inner_public_function();
 
	// bringing path into scope
	use outer_module::inner_module;
	inner_module::inner_public_function();
}

Renaming with as keyword

use std::fmt::Result;
use std::io::Result as IoResult;

Re-exporting with pub use

mod outer_module {
	pub mod inner_module {
		pub fn inner_public_function() {}
	}
}
 
pub use crate::outer_module::inner_module;

Defining modules in separate files

// src/lib.rs
mod my_module;
 
pub fn some_function() {
	my_module::my_function();
}
 
// src/my_module.rs
pub fn my_function() {}

The rust language cheatcode is an adoption form Let's Get Rusty cheatsheet, who has a great inspiration from the Rust community and inspired me to get into rust development. For learning purposes, I'm adding more content for my own learning in rust. Kindly check out his content from here to get the original cheatsheet:

Let's Get Rusty