code: public function parse($value, $rule)
      {
          $rs = $value;
  
          if (!is_array($rs)) {
              $ruleFormat = !empty($rule['format']) ? strtolower($rule['format']) : '';
              if ($ruleFormat == 'explode') {
                  $rs = explode(isset($rule['separator']) ? $rule['separator'] : ',', $rs);
              } else if ($ruleFormat == 'json') {
                  $rs = json_decode($rs, true);
              } else {
                  $rs = [$rs];
              }
          }
  
          $this->filterByRange(count($rs), $rule);
  
          return $rs;
      }
docs: 对数组格式化/数组转换
  
  @param string $value 变量值
  @param array $rule ['name' => '', 'type' => 'array', 'default' => '', 'format' => 'json/explode', 'separator' => '', 'min' => '', 'max' => '']
  @return array