Roblox: OOP Introduction

Object Oriented Programming is a unique style of programming that enables you to define discrete components by creating “objects.” An object is a peice of code that contains data (information) and methods (actions / functions).

Think of classes as blueprints for complex “objects”, in example, we could create a car class, which contains speed, acceleration and weight data. We can also add a method to make it drive

How can we create a class object?

On Roblox, there isn’t a specific keyword like in other languages. We have to use metatables, which are more powerful tables ( they just contain extra internal functions ) For more information about metatables, visit this site: Roblox | Metatables.

In this article, I will give you a brief overview of how to create a simple class

Creating the class

First of all, it is best to create classes inside modules, as you can require modules from different scripts, and it will declutter your main scripts.

Simple definition

Here is a simple class, I will be using a “person” as an example:

-- Class.lua

-- Defining class
local person = {}
person.__index = person

-- Defining constructor
function person.new()
    local self = setmetatable({}, person)

    return self
end

-- Defining method
function person:Action()
    print("Action")
end

-- Return the class 
return person

Now in another script ( preferably a server script for now ), we can require and create the person class

-- Server.lua

local PersonClass = require(path to the module)

local person = PersonClass.new()

-- This is how you can create the 'person' object, 
--   you can now get its data simply by indexing the object,
--   and call methods by using a colon.

-- I will show you how we can add data and methods.

In this snippet, we can see that calling the .new() constructor creates a new metatable for person.

Adding data

We can add data to the person class as so:

-- Class.lua

-- Constructor
function person.new(weight: number, height: number)
    local self = setmetatable({}, person)

    --> Define data
    self.Weight = weight
    self.Height = height

    return self
end

This data is also visible to the script that has the object itself:

-- Server.lua

local PersonClass = require(...)

--> Create person with weight of 5, and height of 10
local person = PersonClass.new( 5, 10 )

-- You can also print out these values by indexing the person:
print(`weight: {person.Weight}, height: {person.Height} `)

Adding class methods

We can also add methods to the class, which act like built-in functions.
These are especially useful as we can use the data contained inside the class with the self keyword.

Here is a simple method that prints out the person’s weight and height:

-- Class.lua

function person:Print()

    -- The self keyword is automatically defined by default ( if you put a colon )
    -- You can use it to get either the object's data or other methods
    -- Here, lets just print out the persons weight & height

    print(self.Weight, self.Height)
end

We can also add another method that can be called from a different method as so:

-- Class.lua

function person:Print()

    -- Using the self keyword, we can call another method
    self:PrintWeight()
    self:PrintHeight()
end

function person:PrintWeight()
    print(self.Weight)
end

function person:PrintHeight()
    print(self.Height)
end

This basically wraps up the first part of my Object Oriented Programming article.