class.lua

A minimal, single-file class system for Lua, built on metatables. Supports single inheritance, runtime type introspection, and works across Lua 5.1–5.4 and LuaJIT.

Features

• Single file, zero dependencies — just copy class.lua into your project.
• Single inheritance via metatable chaining.
• Type introspection — check whether a value is a class instance (IsClassObject) or whether one class derives from another (IsOf).
• Fully annotated with EmmyLua annotations for editor autocompletion.

Installation

Copy the file

Since it's a single file with no dependencies, you can just drop class.lua into your project:

curl -O https://raw.githubusercontent.com/duckifo/class.lua/main/class.lua

Usage

Defining a class.

local Class = require("class")
local Animal = Class.Define("Animal")

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

function Animal:Speak()
    print(self.name .. " makes a sound.")
end

Creating an class instance from a class.

local rex = Animal:New("Rex")
rex:Speak() -- "Rex makes a sound."

Inheritance

local Dog = Class.Define("Dog", Animal)

function Dog:Init(name, toys)
    Animal.Init(self, name) -- Call super class Init method with self.
    self.toys = toys or {}
end

function Dog:Play()
    if #self.toys == 0 then
        print(self.name.." doesn't have any toys to play with :(").
        return
    end

    local toy = self.toys[math.randint(1, #self.toys)]
    print(self.name.." played with their "..toy.." toy.")
end

local dave = Dog:New("Dave", { "ball", "rope" })
dave:Speak() -- "Dave makes a sound."
dave:Play()  -- "Dave played with their ball toy."

Runtime checking.

Class.IsClassObject(dave)      --> true
Class.IsClassObject({})        --> false

Class.IsOf(Animal, dave)       --> true  (Dog derives from Animal)
Class.IsOf(Dog, rex)           --> false (Animal does not derive from Dog)
Class.IsOf(Class.RootClass, dave) --> true (everything derives from RootClass)

Finding a superclass

local Super = Class.Super(Dog) -- returns Animal

API Reference

Function	Description
Class.Define(name, extending?)	Defines a new class. extending defaults to the root class if omitted.
Class:New(...)	Creates a new instance, forwarding arguments to Init.
Class:Init(...)	Interface method meant to be overridden by class.
ClassModule.IsClassObject(value)	Returns true if value is a class instance.
ClassModule.IsOf(base, derived)	Returns true if derived is, or derives from, base.
ClassModule.Super(cls)	Returns the superclass of cls, or nil for the root class.
ClassModule.RootClass	The base class all classes ultimately derive from.

License

MIT — see LICENSE for the full text.

Contributing

Issues and pull requests are welcome.