PHP递归

//模型公众方法，递归
    public function treeLevel(array $data, int $pid = 0, string $html = '--', int $level = 0)
    {
        //静态数组不在方法内，所以无法覆盖
        static $arr = [];
        foreach ($data as $val) {
            if ($val['pid'] == $pid) {
                $val['html'] = str_repeat($html, $level * 2);
                $val['level'] = $level + 1;
                //如果是0，则是顶级菜单
                $arr[] = $val;
                $this->treeLevel($data, $val['id'], $html, $val['level']);
            }
        }
        return $arr;
    }
    //递归处理层
    public function sonLevel($data, $pid = 0)
    {
        $arr = [];
        foreach ($data as $val){
            if ($val['pid'] == $pid){
                $val['son'] = $this->sonLevel($data,$val['id']);
                $arr[] = $val;
            }
        }
        return $arr;
    }