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                ??碼云GVP開源項目 12k star Uniapp+ElementUI 功能強大 支持多語言、二開方便! 廣告
                **一.Nullsafe運算符** #常用于類中屬性和方法返回值. ``` ?-> ``` &emsp; **二.全等于NULL** #注意這兒是全等于(===)不是等于(==). #其他為非NULL 1.未定義 ``` var_dump($a); ``` 2.未返回 ``` function show(){} var_dump(show()); ``` 3.null或NULL ``` $a=null; var_dump($a); ``` &emsp; **三.Nullsafe用法實例** #如果全等于NULL則斷開并返回NULL,如果不全等于NULL則往后繼續執行. 1.類定義 ``` class Person{ public $user; public $country; public function __construct(){ $this->user=$this; $this->country='yes'; } public function getAddress(){ return $this; } } $session=new Person(); ``` 1.舊版本if ``` if($session!==null){ $user = $session->user; if($user!==null){ $address = $user->getAddress(); if($address!=null){ $country = $address->country; if($country!==null){ var_dump($country); } } } } ``` 2.新版本?-> ``` echo $session?->user?->getAddress()?->country ``` &emsp; ### **系統的學習PHP** 關注:PHP自學中心,回復相應的關鍵詞,領取以下視頻教程 **PHP性能優化視頻教程** 公眾號里回復:20181126 &emsp; #### **還有其他的教程的關鍵詞,請關注公眾號查看每天分享的文章教程的頭部** ![](https://img.kancloud.cn/96/af/96af322d2cdc53d3fbbe981affa60c7f_150x150.jpg)
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