在lua中，可以通过元表来实现类、对象、继承等。与元表相关的方法有setmetatable()、__index、getmetatable()、__newindex。

具体什么是元表在这里就不细说了，网上很多介绍，这里主要讲与cocos2dx相关联的部分。

在lua-binding库中extern.lua里，有如下方法：

--Create an class.
function class(classname, super)
    local superType = type(super)
    local cls

    if superType ~= "function" and superType ~= "table" then
        superType = nil
        super = nil
    end

    if superType == "function" or (super and super.__ctype == 1) then
        -- inherited from native C++ Object
        cls = {}

        if superType == "table" then
            -- copy fields from super
            for k,v in pairs(super) do cls[k] = v end
            cls.__create = super.__create
            cls.super    = super
        else
            cls.__create = super
        end

        cls.ctor    = function() end
        cls.__cname = classname
        cls.__ctype = 1

        function cls.new(...)
            local instance = cls.__create(...)
            -- copy fields from class to native object
            for k,v in pairs(cls) do instance[k] = v end
            instance.class = cls
            instance:ctor(...)
            return instance
        end

    else
        -- inherited from Lua Object
        if super then
            cls = clone(super)
            cls.super = super
        else
            cls = {ctor = function() end}
        end

        cls.__cname = classname
        cls.__ctype = 2 -- lua
        cls.__index = cls

        function cls.new(...)
            local instance = setmetatable({}, cls)
            instance.class = cls
            instance:ctor(...)
            return instance
        end
    end

    return cls
end

定义一个类：

MyClass = class("MyClass")
function MyClass:ctor()
	print("MyClass:ctor()")
end

local myclass = MyClass:new()

继承一个类：

GameLayer = class("GameLayer", function()
	local layer = cc.Layer:create()
	return layer
end)
local gamelayer = GameLayer:new()
addChild(gamelayer)