light-class

A lightweight, single-file object-oriented programming (OOP) library for Lua.

Features

Lightweight — a single file with no dependencies.
Simple syntax — an intuitive API for defining classes and inheritance.
Inheritance — supports single inheritance through class.extend.
Metamethods — automatically inherits metamethods (such as __add, __tostring, and so on) from superclasses.
Compatibility — designed for Lua 5.1+, LuaJIT, and Lua 5.4 (it handles __name and __tostring formatting automatically).

Installation

Copy the light-class.lua file into your project directory and require it.

You usually don’t need to do this yourself: light-class is vendored and embedded directly into the nmrp-norm bundle, so it ships with the package.

Usage

Require the library once, then use class.new to declare a class and class.extend to derive from an existing one.

Creating a class

local class = require("light-class")

-- Define a new class
local Dog = class.new("Dog")

-- Constructor
function Dog:__init(name)
    self.name = name
end

-- Method
function Dog:bark()
    print(self.name .. " says Woof!")
end

-- Instantiation
local myDog = Dog("Rex")
myDog:bark() -- Output: Rex says Woof!

__init is the constructor: it runs when you call the class like a function. Methods are declared with the : syntax so they receive self.

Inheritance

Derive a class from another one with class.extend. Call the parent constructor explicitly to reuse its initialization.

local Animal = class.new("Animal")

function Animal:__init(name)
    self.name = name
end

function Animal:speak()
    print("...")
end

-- Create a derived class
local Cat = class.extend("Cat", Animal)

function Cat:__init(name, color)
    -- Call super constructor
    Animal.__init(self, name)
    self.color = color
end

function Cat:speak()
    print(self.name .. " (color: " .. self.color .. ") meows.")
end

local myCat = Cat("Whiskers", "Black")
myCat:speak() -- Output: Whiskers (color: Black) meows.

Overridden methods (like speak) replace the parent version, while any method not overridden is inherited from the superclass.