class.lua

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---- Copyright 2011 Simon Dales
--
-- This work may be distributed and/or modified under the
-- conditions of the LaTeX Project Public License, either version 1.3
-- of this license or (at your option) any later version.
-- The latest version of this license is in
--   http://www.latex-project.org/lppl.txt
--
-- This work has the LPPL maintenance status `maintained'.
-- 
-- The Current Maintainer of this work is Simon Dales.
--

--[[!
  \file 
  \brief enables classes in lua
  ]]
  
--[[ class.lua
-- Compatible with Lua 5.1 (not 5.0).

  ---------------------
  
  ]]--
--! \brief ``declare'' as class
--! 
--! use as:
--! \code{lua}
--! TWibble = class()
--! function TWibble.init(instance)
--!   self.instance = instance
--!   -- more stuff here
--! end
--! \endcode
--!   
function class(BaseClass, ClassInitialiser)
  local newClass = {}    -- a new class newClass
  if not ClassInitialiser and type(BaseClass) == 'function' then
    ClassInitialiser = BaseClass
    BaseClass = nil
  elseif type(BaseClass) == 'table' then
    -- our new class is a shallow copy of the base class!
    for i,v in pairs(BaseClass) do
      newClass[i] = v
    end
    newClass._base = BaseClass
  end
  -- the class will be the metatable for all its newInstanceects,
  -- and they will look up their methods in it.
  newClass.__index = newClass

  -- expose a constructor which can be called by <classname>(<args>)
  local classMetatable = {}
  classMetatable.__call = 
  function(class_tbl, ...)
    local newInstance = {}
    setmetatable(newInstance,newClass)
    --if init then
    --  init(newInstance,...)
    if class_tbl.init then
      class_tbl.init(newInstance,...)
    else 
      -- make sure that any stuff from the base class is initialized!
      if BaseClass and BaseClass.init then
        BaseClass.init(newInstance, ...)
      end
    end
    return newInstance
  end
  newClass.init = ClassInitialiser
  newClass.is_a = 
  function(this, klass)
    local thisMetabable = getmetatable(this)
    while thisMetabable do 
      if thisMetabable == klass then
        return true
      end
      thisMetabable = thisMetabable._base
    end
    return false
  end
  setmetatable(newClass, classMetatable)
  return newClass
end
--eof