do  local Infor_class = {};  function Infor_class.create(_t)   local newTable = {};   setmetatable(newTable, Infor_class); --set the metatable   for i, v in pairs(_t) do    newTable[i] = v;   end   return newTable;  end  function Infor_class.sum(c1, c2)   if(#c1 ~= #c2) then    return nil;   else    local result = {};    local len = #c1;    for i = 1, len do     result[i] = c1[i] + c2[i];    end    print("result");    return result;   end   print("nil");   return nil;  end  Infor_class.__add = Infor_class.sum --override the _add  r1 = Infor_class.create{3, 4}  r2 = Infor_class.create{5, 6};  result = r1 + r2;  print(unpack(result)); end