function clone(object)
    local lookup_table = {}
    local function _copy(object) 
        if type(object) ~= "table" then
            return object
        elseif lookup_table[object] then
            return lookup_table[object]
        end
        local new_table = {}
        lookup_table[object] = new_table
        for key, value in pairs(object) do
            new_table[_copy(key)] = _copy(value)
        end
        return setmetatable(new_table, getmetatable(object))
    end
    return _copy(object)
end

function class(classname, super)
    local superType = type(super)
    local cls
    if superType ~= "function" and superType ~= "table" then
        superType = nil
        super = nil
    end
    if superType == "function" or (super and super.__ctype == 1) then
        cls = {}
        if superType == "table" then
            -- copy fields from super
            for k, v in pairs(super) do
                cls[k] = v
            end
            cls.__create = super.__create
            cls.super = super
        else
            cls.__create = super
            cls.ctor = function()
            end
        end
        cls.__cname = classname
        cls.__ctype = 1
		
        function cls.new(...)
            local instance = cls.__create(...)
            for k, v in pairs(cls) do
                instance[k] = v
            end
            instance.class = cls
            instance:ctor(...)
            return instance
        end
    else
        if super then
            cls = {}
            setmetatable(cls, {__index = super})
            cls.super = super
        else
            cls = {ctor = function()
                end}
        end

        cls.__cname = classname
        cls.__ctype = 2 -- lua
        cls.__index = cls

        function cls.new(...)
            local instance = setmetatable({}, cls)
            instance.class = cls
            instance:ctor(...)
            return instance
        end
    end

    return cls
end