code: public function add($member, ...$members): int
      {
          array_unshift($members, $member);
  
          return $this->redis->sadd($this->key, $this->serializeArray($members));
      }
docs: @param mixed $member     First member that's added to the list.
  @param mixed ...$members More members to add.
  
  @return int Amount of newly added members in set.