Classes And Methods Example

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Class and Methods implementation for Lua

After the initial euphoria of having discovered Lua, one of the greatest scripting languages ever, passed I started to play around with classes and methods. I looked at various implementations and found Christian Lindig's (lindig |at| cs.uni-sb.de) to be the neatest way. I noted, however, that there was room for improvement to make it more dummy proof. To Christian Lindig's code I added the ability to easily add class constructors without dealing with obj directly.

How to use INC_Class.lua

The following code shows an example of the class constructor and inheritance features. Notice how class cTiger inherits from cAnimal by :

cTiger = setclass("Tiger", cAnimal)

and notice that if you have a method for the class called 'init', the code will automatically execute when you call class:new()

Example code:

require("INC_Class.lua")



--===========================



cAnimal=setclass("Animal")



function cAnimal.methods:init(action, cutename) 

	self.superaction = action

	self.supercutename = cutename

end



--==========================



cTiger=setclass("Tiger", cAnimal)



function cTiger.methods:init(cutename) 

	self:init_super("HUNT (Tiger)", "Zoo Animal (Tiger)")

	self.action = "ROAR FOR ME!!"

	self.cutename = cutename

end



--==========================



Tiger1 = cAnimal:new("HUNT", "Zoo Animal")

Tiger2 = cTiger:new("Mr Grumpy")

Tiger3 = cTiger:new("Mr Hungry")



print("CLASSNAME FOR TIGER1 = ", Tiger1:classname())   

print("CLASSNAME FOR TIGER2 = ", Tiger2:classname()) 

print("CLASSNAME FOR TIGER3 = ", Tiger3:classname()) 

print("===============")

print("SUPER ACTION",Tiger1.superaction)

print("SUPER CUTENAME",Tiger1.supercutename)

print("ACTION        ",Tiger1.action)

print("CUTENAME",Tiger1.cutename)

print("===============")

print("SUPER ACTION",Tiger2.superaction)

print("SUPER CUTENAME",Tiger2.supercutename)

print("ACTION        ",Tiger2.action)

print("CUTENAME",Tiger2.cutename)

print("===============")

print("SUPER ACTION",Tiger3.superaction)

print("SUPER CUTENAME",Tiger3.supercutename)

print("ACTION        ",Tiger3.action)

print("CUTENAME",Tiger3.cutename)

Class Implementation

-----------------------------------------------------

---- SETCLASS CLONES THE BASIC OBJECT CLASS TO CREATE NEW CLASSES

-----------------------------------------------------

-- Supports INHERITANCE 

--

-- Sam Lie, 17 May 2004 

-- Modified Code from Christian Lindig - lindig (at) cs.uni-sb.de

---------------------------------------------------------------



-- EVERYTHING INHERITS FROM THIS BASIC OBJECT CLASS

BaseObject = {

  super   = nil,

  name    = "Object",

  new     =

    function(class)

      local obj  = {class = class}

      local meta = {

        __index = function(self,key) return class.methods[key] end 

      }            

      setmetatable(obj,meta)

      return obj

    end,

  methods = {classname = function(self) return(self.class.name) end},

  data    = {}

}



function setclass(name, super)

  if (super == nil) then

    super = BaseObject

  end



  local class = {

    super = super; 

    name  = name; 

    new   =

      function(self, ...) 

        local obj = super.new(self, "___CREATE_ONLY___");

          -- check if calling function init

          -- pass arguments into init function

        if (super.methods.init) then

          obj.init_super = super.methods.init

        end



	if (self.methods.init) then

            if (tostring(arg[1]) ~= "___CREATE_ONLY___") then

              obj.init = self.methods.init

              if obj.init then

                obj:init(unpack(arg))

              end

            end

	end



        return obj

      end,  

    methods = {}

  }

    

  -- if class slot unavailable, check super class

  -- if applied to argument, pass it to the class method new        

  setmetatable(class, {

    __index = function(self,key) return self.super[key] end,

    __call  = function(self,...) return self.new(self,unpack(arg)) end 

  })



  -- if instance method unavailable, check method slot in super class    

  setmetatable(class.methods, {

    __index = function(self,key) return class.super.methods[key] end

  })

  return class

end    

dontspamme_sam_lie2000@yahoo.com, 17 May 2004

See Also

• ObjectOrientedProgramming