-- from http://lua-users.org/wiki/SimpleLuaClasses

function Class(base, _ctor)
	local c = {}    -- a new class instance
	if not _ctor and type(base) == 'function' then
		_ctor = 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 c._ctor then
			c._ctor(obj,...)
		end
		return obj
	end

	c._ctor = _ctor
	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