Variables & Constants

Variables and constants let you store information in your program. If you’re just getting started, you can think of them as labeled containers:

A variable is a container you can change.
A constant is a container you fill once and never change again.

Since Ferret can automatically figure out the type of a value, you don’t need to introduce types yet. You only need to understand how to declare names and give them values.

Ferret provides two keywords for this: let for variables and const for constants.

Variable Declaration

Use let to create a variable. A variable can change later. We use := to declare with a value. You will learn about the := (walrus) operator and why we did not use = later. Just remember to use := when you are declaring a variable or constant for the first time with a value.

Basic Variable Examples

let name := "Ferret";
let age := 1;
let score := 10;

Reassigning Variables

Variables can be updated using the = operator. It’s called the assignment operator.

let points := 0;
points = 15;
points = 30;

Constants

Constants use const. Once a constant gets a value, it cannot change.

const PI := 3.14159;
const MAX_RETRIES := 3;
const APP_NAME := "Ferret Compiler";

Attempting to Reassign

const VERSION := 1;
VERSION = 2;  // ERROR: Cannot assign to constant

Naming Conventions

To keep code readable:

Use snake_case for variables: user_name, total_count
Use SCREAMING_SNAKE_CASE for constants: MAX_VALUE, DEFAULT_PORT

let user_name := "Alice";
let total_count := 42;

const DEFAULT_PORT := 8080;