在类的构造函数中返回一个值 [英] Returning a value in constructor function of a class

问题描述

到目前为止，我有一个带有构造函数的 PHP 类

So far I have a PHP class with the constructor

public function __construct ($identifier = NULL)
{
 // Return me.
if ( $identifier != NULL )
{
  $this->emailAddress = $identifier;
  if ($this->loadUser() )
    return $this;      
  else
  {
// registered user requested , but not found ! 
return false;
  }
}

loadUser 的功能是在数据库中查找特定的电子邮件地址.当我将标识符设置为某个电子邮件时，我确定它不在数据库中；第一个 IF 被通过，然后转到第一个 ELSE.这里构造函数应该返回 FALSE；相反，它返回一个包含所有 NULL 值的类对象！

the functionality of loadUser is to look up the database for a particular email address. When i set the identifier to some email that i'm sure it's not in the database; the first IF is get passed, and goes to the first ELSE. here the constructor should return FALSE; but instead, it returns an object of the class with all NULL values !

我如何防止这种情况发生?谢谢

how do i prevent this? thanks

谢谢大家的回答.那是相当快的！我看到 OOP 的方式是抛出一个异常.所以抛出一个，我的问题改变了我应该如何处理异常?php.net 的手册非常混乱！

thank you all for the answers. that was quite fast ! I see that the OOP way is to throw an Exception. So a throw one, my question changes that what should i do with the exception?? php.net's manual is pretty confusing !

    // Setup the user ( we assume he is a user first. referees, admins are   considered users too )
    try { $him = new user ($_emailAddress);
    } catch (Exception $e_u) { 
      // try the groups database
      try { $him = new group ($_emailAddress); 
      } catch (Exception $e_g) {
          // email address was not in any of them !!  
        }
    }

推荐答案

构造函数不获取返回值；它们完全用于实例化类.

Constructors don't get return values; they serve entirely to instantiate the class.

在不重构您已经在做的事情的情况下，您可以考虑在此处使用异常.

Without restructuring what you are already doing, you may consider using an exception here.

public function __construct ($identifier = NULL)
{
  $this->emailAddress = $identifier;
  $this->loadUser();
}

private function loadUser ()
{
    // try to load the user
    if (/* not able to load user */) {
        throw new Exception('Unable to load user using identifier: ' . $this->identifier);
    }
}

现在，您可以以这种方式创建一个新用户.

Now, you can create a new user in this fashion.

try {
    $user = new User('[e-mail]');
} catch (Exception $e) {
    // unable to create the user using that id, handle the exception
}

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