object.lua

-- The base object `Object`
local Object = {}
Object.meta = {__index = Object}

-- Create a new instance of this object  
function Object:create()
  local meta = rawget(self, "meta")
  if not meta then error("Cannot inherit from instance object") end
  return setmetatable({}, meta)
end

-- Create a new instance and call constructor if there is one
function Object:new(...)
  local obj = self:create()
  if type(obj.initialize) == "function" then
    obj:initialize(...)
  end
  return obj
end

-- Extend this object into a new prototype object
function Object:extend()
  local obj = self:create()
  obj.meta = {__index = obj}
  return obj
end



p("Object", Object)

local Rectangle = Object:extend()

function Rectangle:initialize(w, h)
  self.w = w
  self.h = h
end

function Rectangle:getArea()
  return self.w * self.h
end

p("Rectangle", Rectangle)

local r = Rectangle:new(2, 3)
p("r, r:getArea()", r, r:getArea())
  
local Square = Rectangle:extend()
function Square:initialize(w)
  self.w = w
  self.h = w
end

p("Square", Square)

local s = Square:new(4)
p("s, s:getArea()", s, s:getArea())

output.txt

"Object"	{ extend = function: 0x409910c0, meta = { __index = table: 0x4098f7b8 }, create = function: 0x4098f7e0, new = function: 0x40991038 }
"Rectangle"	{ meta = { __index = table: 0x4097e528 }, initialize = function: 0x40991cb8, getArea = function: 0x40992068 }
"r, r:getArea()"	{ h = 3, w = 2 }	6
"Square"	{ initialize = function: 0x40992cd0, meta = { __index = table: 0x40992c10 } }
"s, s:getArea()"	{ h = 4, w = 4 }	16