Rustlang an introduction

Rustlang an introduction

Variables:

Variables in Rust are immutable by default, by design as well. The immutability helps rust achieve among others the goals of safety and easy concurrency. Defining variables is pretty standard.

A variable x assigned to the integer 5 is shown below, although rust is statically typed in some instances like one below it can infer the data type without an explicit annotation. A semi-colon is also required indicative of statement termination.

let x = 5;

An annotated version of the variable defined above would be:

let x: i32 = 5;

We can test the immutability of variables, by trying to reassingn the x variable:

fn main() {
    let x = 5;
    println!("original value of x is {x}");
    x = 10;
    println!("new value of x is {x}");
}

Trying to compile the above code returns the error:

error[E0384]: cannot assign twice to immutable variable `x`
 --> src/main.rs:5:2
  |
3 |     let x = 5;
  |         -
  |         |
  |         first assignment to `x`
  |         help: consider making this binding mutable: `mut x`
4 |     println!("original value of x is {x}");
5 |     x = 10;
  |     ^^^^^^ cannot assign twice to immutable variable

For more information about this error, try `rustc --explain E0384`.
error: could not compile `playground` due to previous error

However, variables can be mutated by adding the keyword mut before the variable name. E.g.

fn main() {
	let mut x = 5;
    	println!("original value of x is {x}");
	x = 10;
	println!("new value of x is {x}");
}

Compiling and executing the code above returns the result:

Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 1.21s
     Running `target/debug/playground`

original value of x is 5
new value of x is 10

Constant variables

A group of immutabilities that can never be mutated are constant variables. Unlike regular variables the mut keyword has no effect on these. Constant variables also mandate annotation, and do not compile otherwise. They can be defined using the syntax:

const URL: &str = "https://mainakamau92.github.io/"

Some more variables with different types

Floating points:

let flt:f32 = 3.1415;
let flt:f64 = 3.14159265359;

Char (supports all unicode characters and is demarcted by single quotes):

let emoji:char = '🤣';

String literals:

let hello:&str = "Hello, World!";