This video is part 4 of a series:

1. Lua Style Guide
   1. Formatting with StyLua
2. Lua Scripting Best Practices
3. Organizing Lua Code With Modules
4. Module Best Practices ← You Are Here

This guide provides an overview of common types of Lua modules and best practices for each, building off of the basics described in Organizing Lua Code With Modules.

Write Stateless Modules

In general, module tables should not contain any internal state. By separating the module's state from its behavior, the code becomes more modular and independent, allowing for easier testing and debugging. It also allows modules can be more easily shared between projects and reused in different contexts.

Instead, either pass state in as a function parameter or use class instances to hold state.

-- GOOD: a stateless module
local Bank = {}

function Bank.Deposit(account, amount)
	return acount.balance = account.balance + amount
end

function Bank.Withdraw(account, amount)
	if account.balance < amount then
		DCEI.LogError("Insufficient funds")
	else
		return account.balance - amount
	end
end

return Bank

-- BAD: a stateful module
local Bank = {}

local balance = 0

function Bank.Deposit(amount)
	return balance = balance + amount
end

function Bank.Withdraw(amount)
	if balance < amount then
		DCEI.LogError("Insufficient funds")
	else
		return balance - amount
	end
end

return Bank

When to Use Class Method Syntax

In Lua, you should use the : function syntax when defining methods for class instances. This allows you to implicitly pass the instance as the first parameter to the function. Note that class instances are variables that use lower_snake_case styling.

Meanwhile, you should use the . function syntax when defining regular functions that don't belong to class instances. Note that modules use PascalCase styling.