Inline Shape Annotations

In Lua you've been using tables as records for a long time: local user = {name = "Ana", age = 20}. Nothing stops you from misspelling a field, forgetting one, or storing a string where a number belongs. You only find out when the code runs.

Luau lets you describe the shape of such a table right in the declaration, listing each field and its type between curly braces:

local user: {name: string, age: number} = {
    name = "Ana",
    age = 20,
}

Compare this with the table types you already know: {number} describes an array and {[string]: number} describes a map with any string keys. A shape is more precise. It names each field individually and gives every field its own type.

Once the shape is declared, the type checker verifies the table against it while you edit. A missing field or a wrong value type is flagged before the code ever runs:

local user: {name: string, age: number} = {
    name = "Ana",
    age = "twenty", -- ✗ type error: string is not a number
}

As always, the annotation adds no runtime behavior: the table is a plain Lua table. Inline shapes are perfect for one-off structures you don't plan to reuse; in the next lesson you'll give shapes a name.