Lua is not a Object-Oriented language. If we want to use concepts like “class, constructor, desctructor, member function”, we must use table or metatable to simulate.

<Programming In Lua> introduces a method to implement OO in lua. http://www.lua.org/pil/16.html

    Account = { balance=0,
                withdraw = function (self, v)
                             self.balance = self.balance - v
                           end
              }
    
    function Account:deposit (v)
      self.balance = self.balance + v
    end
    
    Account.deposit(Account, 200.00)
    Account:withdraw(100.00)

Another sample is for privated data:

    function newAccount (initialBalance)
      local self = {balance = initialBalance}
    
      local withdraw = function (v)
                         self.balance = self.balance - v
                       end
    
      local deposit = function (v)
                        self.balance = self.balance + v
                      end
    
      local getBalance = function () return self.balance end
    
      return {
        withdraw = withdraw,
        deposit = deposit,
        getBalance = getBalance
      }
    end

CloudWu (famous chinese game maker) introduces another method for OO implementation http://blog.codingnow.com/cloud/LuaOO.

###################

Lua has a important advantage, that is it could use module mechanism.

I will introduce some awesome modules for OO implementation in Lua.

First one is LOOP, its website is http://loop.luaforge.net, you could download release file in website and put to your lua installation directory.

A good example is like following.

local oo = require “loop.simple”

Circle = oo.class()
function Circle:diameter()
  return self.radius * 2
end
function Circle:circumference()
  return self:diameter() * 3.14159
end
function Circle:area()
  return self.radius * self.radius * 3.14159
end

Sphere = oo.class({}, Circle)
function Sphere:area()
  return 4 * self.radius * self.radius * 3.14159
end
function Sphere:volume()
  return 4 * 3.14159 * self.radius^3 / 3
end

function show(shape)
  print(“Shape Characteristics”)
  print(”  Side:         “, shape.radius)
  print(”  Diameter:     “, shape:diameter())
  print(”  Circumference:”, shape:circumference())
  print(”  Area:         “, shape:area())
  if oo.instanceof(shape, Sphere) then
    print(”  Volume:        “, shape:volume())
  end
end

c = Circle{ radius = 20.25 }
s = Sphere{ radius = 20.25 }

show(c)
show(s)

Another active project for OO in Lua is lua-coat http://lua-coat.luaforge.net/.

require ‘Coat’

class ‘Point’

has.x = { is = ‘rw’, isa = ‘number’, default = 0 }
has.y = { is = ‘rw’, isa = ‘number’, default = 0 }

overload.__tostring = function (self)
    return ‘(‘ .. self:x() .. ‘, ‘ .. self:y() .. ‘)’
end

method.draw = function (self)
    return “drawing ” .. self._CLASS .. tostring(self)
end

local p1 = Point{ x = 1, y = 2 }
print(p1:draw())

You could find some other projects in luaforge. For example, http://luaforge.net/projects/los/

http://luaforge.net/projects/sool/

http://luaforge.net/projects/mnoo/

In lua-users, you could find a good item for Lua-OO.

http://lua-users.org/wiki/ObjectOrientedProgramming