The Enum Pattern in Luau

Programs are full of values drawn from a small, fixed set: an order is pending, shipped or delivered; a player faces up, down, left or right. Many languages have an enum keyword for this. Luau does not, and it doesn't need one, because two tools you already own cover the job.

Pattern 1: the constant table. A plain table maps meaningful names to values, replacing "magic numbers" scattered through the code:

local Status = {
    Pending = 1,
    Active = 2,
    Done = 3,
}

print(Status.Active) -- 2

This is a real runtime value: you can read Status.Active, compare against it, and pass it around, just like the tables you've used all along.

Pattern 2: the literal union. A type made of exact string values, using the literal types you met in the unions chapter:

type Color = "red" | "green" | "blue"
local favorite: Color = "green" -- ✓
local oops: Color = "yellow"    -- ✗ type error

The union exists only for the checker, zero runtime cost, but it guarantees a variable can hold nothing outside the set. The two patterns complement each other: the table gives you runtime values under one name; the union gives you a compile-time guarantee. Later in this chapter you'll also meet table.freeze, which protects a constant table from being modified at runtime.