light_world.lua/lib/class.lua

-- class.lua
-- Compatible with Lua 5.1 (not 5.0).
local class = function(base, init)
   local c = {}    -- a new class instance
   if not init and type(base) == 'function' then
      init = base
      base = nil
   elseif type(base) == 'table' then
    -- our new class is a shallow copy of the base class!
      for i,v in pairs(base) do
         c[i] = v
      end
      c._base = base
   end
   -- the class will be the metatable for all its objects,
   -- and they will look up their methods in it.
   c.__index = c

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

return class