PHP构造函数返回一个NULL [英] PHP constructor to return a NULL

问题描述

我有这个代码。一个 User 对象构造函数可能会失败，因此 $ this-> LoggedUser c $ c> NULL 值，并在构造函数返回后释放对象？

I have this code. Is it possible for a User object constructor to somehow fail so that $this->LoggedUser is assigned a NULL value and the object is freed after constructor returns?

$this->LoggedUser = NULL;
if ($_SESSION['verbiste_user'] != false)
  $this->LoggedUser = new User($_SESSION['verbiste_user']);    

推荐答案

假设你使用PHP 5，构造函数中的异常：

Assuming you're using PHP 5, you can throw an exception in the constructor:

class NotFoundException extends Exception {}

class User {
    public function __construct($id) {
        if (!$this->loadById($id)) {
             throw new NotFoundException();
        }
    }
}

$this->LoggedUser = NULL;
if ($_SESSION['verbiste_user'] != false) {
    try {
        $this->LoggedUser = new User($_SESSION['verbiste_user']);
    } catch (NotFoundException $e) {}
}

你可以将它包装在一个静态的工厂方法中：

For clarity, you could wrap this in a static factory method:

class User {
    public static function load($id) {
        try {
            return new User($id);
        } catch (NotFoundException $unfe) {
            return null;
        }
    }
    // class body here...
}

$this->LoggedUser = NULL;
if ($_SESSION['verbiste_user'] != false)
    $this->LoggedUser = User::load($_SESSION['verbiste_user']);

另外，有些版本的PHP 4允许你在构造函数中将$ this设置为NULL，我认为从来没有正式批准，特色最终被删除。

As an aside, some versions of PHP 4 allowed you to set $this to NULL inside the constructor but I don't think was ever officially sanctioned and the 'feature' was eventually removed.

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