lua 复制table

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 newObject = {}

        lookup_table[object] = newObject

        for key, value in pairs(object) do

            newObject[_copy(key)] = _copy(value)

        end

        return setmetatable(newObject, getmetatable(object))

    end

    return _copy(object)

end