Rustlers Atom 1.4 - Variables, binding, shadowing, mutability

Rust variables are bindings: a name tied to a value. By default, they are immutable.

Immutable vs mutable

fn main() {
    let x = 5;
    // x = 6; ❌ compile error

    let mut y = 5;
    y = 6; // ✅ works
    println!("y = {}", y);
}

The mut keyword makes intent explicit. No silent mutation is allowed in rust.

Shadowing

Instead of mutating, you can re-declare the same name.

fn main() {
    let spaces = "   ";
    let spaces = spaces.len(); // new binding, new type
    println!("spaces = {}", spaces);

Every let creates a new binding, and the old one is gone. Bindings live inside their scope. Shadowing can narrow scope deliberately.

Constants

Use const for compile-time values.

const MAX_SCORE: u32 = 100;

fn main() {
    println!("MAX_SCORE = {}", MAX_SCORE);
}

Constants require an explicit type and are always immutable. Following best practices, constants should be named using upper snake case.