Luau Type System

When to Load

Load for Luau type system work: annotations, generics, union types, type narrowing, sealed/unsealed tables, strictness modes (--!strict vs --!nonstrict), module type exports, and metatable-backed object typing. For syntax questions, use roblox-luau-core. For OOP/async/modules, use roblox-luau-patterns.

Quick Reference

Strictness: Use --!strict for maintained code, --!nonstrict while transitioning, and --!nocheck only for legacy/generated code. Project settings and directives select the mode; do not assume one global default.

Inference philosophy: Infer first, annotate boundaries (params, returns, exports). Don't annotate every local. Noise hides signal.

Sealed vs unsealed tables:

local t = {}          -- unsealed: can add fields
t.x = 1               -- OK