Lualass

Table of content

• Description
• Methods
• Samples

Description

This is a very lightweight Lua module that helps simplify faking object-oriented programming, very easy and simple to use, almost plug'n play I'd say.

Methods

Method	Description	Usage
derive(class)	Derive a class based on another one	local Dog = Animal:derive("Dog")
getType()	Get the class's type (name)	Dog:getType()
is(class)	Check if a class is based on another one	Dog:is(Animal)
count()	Return the number of properties of a class	Cat:count()
tostring()	Display a class's information	Animal:tostring()

Samples

I. Creating a new class

It's preferable to create an entirely new file, and create a class there, as follows;

-- “animal.lua” file

local Lualass = require("lualass")
local Animal = Lualass:derive("Animal")

function Animal:new(name, weight)
    self.name = name
    self.weight = weight
end

function Animal:soundOff()
    return "Uh?"
end

return Animal

II. Inheritance

In order to create another class and inherit from the Animal class, we need to create a new file and place our derived class there;

-- “dog.lua” file

local Animal = require("animal")
local Dog = Animal:derive("Dog")

function Dog:new(name, weight, speed)
    self.name = name
    self.weight = weight
    self.speed = speed
end

function Dog:soundOff()
    return "Woof"
end

return Dog

Just like that, we have created 2 classes, with the second class Dog inheriting from the first class Animal. now, if we want to create yet another class, we can do so;

-- “pug.lua” file

local Dog = require("dog")
local Pug = Dog:derive("Pug")

function Pug:new(name, weight, speed, color)
    self.name = name
    self.weight = weight
    self.speed = speed
    self.color = color
end

return Pug

and that's it, notice that we don't have to override the soundOff() method because we want out pugs to produce the same bark.

III. Testing

Now for testing, we can set off a simple main.lua file (it can be called anything), and require the 3 files.

-- “main.lua” file

local Animal = require("animal")
local Dog = require("dog")
local Pug = require("pug")

function main()
    animals = {
        Dog("Spot", 23.45, 59.36),
        Animal("Spurtle", 41.00),
        Pug("Edgar", 20.15, 23.30, "Orange")
    }

    for k,v in pairs(animals) do
        print(v:tostring())
        print(v:getType().."s go "..v:soundOff())
        print("-----------")
    end

    print(animals[1]:is(animals[2]))
    print(animals[2]:is(animals[3]))
    print(animals[3]:is(animals[1]))
end

main();

Notice how we don't have to call the Class:new method, but rather call the table as if it was a function, trying to for a more constructor like syntax, the output would be like this;

Dog = { speed = 59.36, name = Spot, type = Friendly, weight = 23.45 }
Dogs go Woof
-----------
Animal = { name = Spurtle, type = SWAT, weight = 41.0 }
Animals go Uh?
-----------
Pug = { color = Orange, name = Marcel, type = Friendly, weight = 20.15, speed = 23.3 }
Pugs go Woof
-----------
true
false
true

IV. Method overriding

Let's edit the Pug class and override the soundOff() method;

-- “pug.lua” file

local Dog = require("dog")
local Pug = Dog:derive("Pug")

function Pug:new(name, weight, speed, color)
    self.name = name
    self.weight = weight
    self.speed = speed
    self.color = color
end

function Pug:soundOff()
    return "Wooffyy"
end

return Pug

Now let's run another test and see the how the it goes;

-- “main.lua” file

local Animal = require("animal")
local Dog = require("dog")
local Pug = require("pug")

function main()
    animals = {
        Dog("Spot", 23.45, 59.36),
        Animal("Spurtle", 41.00),
        Pug("Edgar", 20.15, 23.30, "Orange")
    }

    for k,v in pairs(animals) do
        print(v:getType().."s go "..v:soundOff())
    end
end

main();

The output is going to be like this;

Dogs go Woof
Animals go Uh?
Pugs go Wooffyy