Lua Basics

Idiomatic, performant Lua patterns for FiveM: functions, tables, variables, conditionals and errors.

Activation Contract

Load this skill when writing or reviewing any Lua in a FiveM resource, or when the user asks about Lua naming, structure, performance, tables or error handling.

Hard Rules

Naming: ALL_CAPS constants, camelCase locals, PascalCase globals, _ for unused variables.
Prefer local; declare locals as close to first use as possible; group file-level globals at the top of a single client/server file.
Do not use table.insert; append with t[#t + 1] = v or maintain your own size counter.
Iterate arrays with numeric for i = 1, #t; imply array indices ({ a, b }) instead of writing them out.
Extract repeated table dereferences into locals; use t.key for constant keys and t[var] for dynamic keys.
Use guard clauses and early returns; never write if x then return true else return false end.
Prefer positive boolean expressions; set defaults with value = value or default.
Use assert for pre-conditions instead of if not x then error() end; fail loudly on unexpected state; return errors as values for expected failures.
Limit parameters; avoid boolean parameters in APIs (use enums); pass named local functions instead of inline ones.
Keep functions small, single-level of abstraction, and document exports.

Decision Gates

Situation	Pattern
Expected failure (not found, invalid input)	return `nil, err` or `false`
Programmer error / impossible state	`assert` / `error`
Flag with more than two meanings	enum table, not boolean
Function reused more than once as argument	`local function` then pass by name
Append to array	`t[#t + 1] = v`

Execution Steps

Apply naming and scope rules to every identifier.
Replace nested if with guard clauses.
Replace table.insert and pairs on arrays with index writes and numeric loops.
Add assert pre-conditions at function entry.
Re-read for size: split any function mixing high- and low-level code.

Output Contract

Return Lua that follows the naming, locality, table and error-handling rules above; annotate any deliberate deviation.

References

rules/functions.md — size, naming, parameters, exports, guard clauses.
rules/tables.md — indices, dereferencing, table.insert, iteration, size.
rules/variables.md — naming, enums vs booleans, declaration location.
rules/conditionals.md — defaults, boolean expressions, readability.
rules/errors.md — assert, pre-conditions, errors as values, fail loudly.
rules/reference-links.md — official Lua and FiveM documentation.

Upstream docs: https://www.lua.org/manual/5.4/

lua-basics