Laravel，我遇到语法错误，意外出现“ $ this”（T_VARIABLE）

Question

我有这样的方法

function manage(Request $params) {
   $orderBy = $params->order;
   $show = function($filter) {
      switch ($filter) {
         case 'published':
            return 1;
            break;
         case 'draft':
            return 2;
            break;
         case 'pending':
            return 0;
            break;
         default :
            return false;
      }
   }

   $this->pagination = $params->pagination ?? 10;

   if (Auth::id() == 1) {
      $post = Post::where('status', $show($params->show) ?? true)
                  ->orderBy($orderBy ?? 'created_at')                
                  ->paginate(10);

   } else {

      $post = Post::where('user_id', Auth::id())
                  ->where('status', $show($params->show) ?? true)
                  ->orderBy($orderBy ?? 'created_at')                
                  ->paginate(10);

   }

   return view('dashboard.post.manage')->with(['post' => $post]);
}

我有这样的错误

syntax error, unexpected '$this' (T_VARIABLE)

我在$this->pagination = $params->pagination ?? 10;附近感觉到错误

我已经检查了代码，但是我找不到错误，请检查我的代码