Learning Rust

One of the first things I like to do after gaining some familiarity with a language is a couple of katas, maybe Blackjack, an API of some sort. All test driven of course. Thats what we'll do here. Check out my rust repo.


Rust is a (system language)[https://en.wikipedia.org/wiki/System_programming_language], meaning it can be used for low level stuff such as Operating Systems, hardware and the like. That doesn't mean it is limited to those however.

Why Rust? Type safety, concurrency, blazingly fast.Rust has a steep learning curve however.


Rust has an opinionated coding style:

  • indentations are 4 spaces
  • variable names are snake case

But, before fundamentals, lets talk about the build runner, documentation generator, test runner and package manager - Cargo.


Assuming you have installed Rust, go ahead and run this:

cargo new hello

This creates a folder:

└── hello
    ├── Cargo.toml
    └── src
        └── main.rs


name = "hello"
version = "0.1.0"
authors = ["Your Name <you@your-email.com>"]
edition = "2018"

See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html


And the rust file:

fn main() {
    println!("Hello, world!");

First things first, the Cargo.toml file. This is the configuration file for your software. This has all the information about your project, the name, authors, version (semver) etc. It is also where you add your dependencies.

The rust file that is generated is a 'hello world' by default.

Now you can create an executable by running cargo build. Then execute by running cargo run (cargo run by itself builds and then runs).

After you run build you will see a 'target' folder is created. in the target folder is 'debug', so you probably want to add this to your .gitignore file.


The genesis of your project is the main function. This is what is executed when you run.

fn main() {}

Functions are delcaried with a fn then name, parenthesis, then the body is in braces.


Integers are signed or unsigned: 8, 16, 32, 64, 128 (usize and isize). i32 or u32 etc.

You can use binary: 0b, octal: 0o, hex: 0x.

Floats are f32 and f64. This is valid: 0.1, this is not: .1.

Bool is bool, which are true and false.

A char is 4 bytes, a scalar, differing from a character within a string, which is utf-8 2 bytes.

Tuple stores multiple values, accessed by dot syntax (maximum of 12):

let a = (1, 2, 3);
println!("{}, {}, {}", a.0, a.1, a.2);

Arrays are limited to 32 length. Vectors are preferred over Arrays.


Variables are immutable in Rust, however, you can mutate them. Variables are declared using let. So Rust is strongly typed, but if it can deduce what the variable is, it will automatically create that type for you.

let [mut] [variable-name][: type] = [value];

Just so we can see something, Rust uses the format println! to write to the console, more on this later, but notice the exclamation mark before the parenthesis. Also, when you see a {} that means it will be replaced by the params you pass after the string.

let a = 34;
println!("Rust can deduce what type you want: {}", a);

let a:u32 = 34; println!("Or, you could add the unsigned integer 32 bit :u32 type {}", a);

let mut change = 34; change += 1; println!("This value is mutable, therefore changed {}", change);

let string = "Hello world!"; println!("{}", string);

We'll come back to strings.

const always uses SCREAMING snake case, and you MUST specify type. Consts are really fast to access. You can use them 'globally' i.e. outside functions.

const UNCHANGING:u32 = 123;
println!("Const value is {}", UNCHANGING);

You can destructure values and assign like this:

let (var1, var2) = (1, 2);

Help from the Compiler

When you get compile errors, Rust gives you a handy explain command: rustc --explain E0384. Run that to get more information on the error. Pretty useful stuff.

Blocks and Scope

Scope in Rust is block level. It does have access to parent scope (nested blocks). A block can be created with braces {}, as in:

fn main() {
        let x = 1;
        println!("{}", x);

Variables can also be 'shadowed', so you can declare the same variable name multiple times.


fn [snake_case function name]([param :type]) -> [return type]

For example:

fn volume(x: i32, y: i32, z: i32) -> i32 {
    return x * y * z;

With the returned value, if you leave off the trailing semicolon of an expression, that value gets returned. (remember, an expression is anything that results in a value).

fn volume(x: i32, y: i32, z: i32) -> i32 {
    x * y * z

Note: you know the println!, see the exclamation mark? That is a 'macro'. A macro is a type of function (more later). You can use macros when you do not have a fixed arity.




Like all good languages, testing is built in to Rust.


Crates coming soon

Ownership and References

Coming soon