Variables and Mutability

Variables

Variables are declared with let, and require a type annotation and an initial value:

let x: i32 = 42;
let flag: bool = true;

Inference does not infer types — every variable must have an explicit type annotation.

Variables are immutable by default. Use let mut to allow reassignment:

let x: i32 = 5;
// x = 6;  // compiler error: x is not mutable

let mut y: i32 = 5;
y = 6;  // OK

Constants are declared with const and must be initialized with a literal value:

const MAX_SIZE: i32 = 100;
const THRESHOLD: i64 = 50000;
const ENABLED: bool = true;