为什么调用父构造函数时会出现致命错误？ [英] Why am I getting Fatal error when calling a parent's constructor?

问题描述

我扩展了一个SPL（标准PHP库）类，我无法调用父的构造函数。这是我得到的错误：

致命错误：无法调用构造函数

这是指向 SplQueue 的文档的链接： http://www.php.net/manual/en/class.splqueue.php

这里是我的代码：

  $ queue = new Queue（）; 
 
 class Queue extends SplQueue {
 
 public function __construct（）{
 echo'before'; 
 parent :: __ construct（）; 
 echo'我已经在父构造函数调用'; 
} 
 
} 
 
退出;什么可能阻止我调用父的构造函数？
 =h2_lin>解决方案
  SplQueue 继承自 SplDoublyLinkedList 。这些类都不定义自己的构造函数。因此，没有显式的父构造函数来调用，你会得到这样的错误。文档在这一点上有点误导（因为它是许多SPL类）。
 
 
 
要解决错误，不要调用父构造函数。
 
 
 
 
 
 
现在，在大多数面向对象语言中，你会期望默认构造函数没有在类中声明的显式构造函数。但是这里的catch： PHP类没有默认构造函数。一个类有一个构造函数 if和只有一个被定义。
 
 
 
事实上，使用反射来分析 stdClass 类，我们看到即使没有构造函数：
  $ c = new ReflectionClass（'stdClass'）; 
 var_dump（$ c-> getConstructor（））; // NULL 
  
尝试反映 SplQueue的构造函数和 SplDoublyLinkedList 都会产生 NULL 。
 
 
 
我的猜测是，当你告诉PHP实例化一个类，它执行所有的内部存储器分配，它需要为新的对象，然后寻找一个构造函数定义，并调用它只有定义 __ construct（）或< class name>（）。我去看看源代码，看起来PHP只是出了问题，当它不能找到一个构造函数调用，因为你在一个子类中明确地告诉它（见 zend_vm_def。 h ）。
 
I am extending one of the SPL (Standard PHP Library) classes and I am unable to call the parent's constructor. Here is the error I am getting:

  
Fatal error: Cannot call constructor
Here is a link to the SplQueue's documentation: http://www.php.net/manual/en/class.splqueue.php

Here is my code:
$queue = new Queue();

class Queue extends SplQueue {

    public function __construct() {
        echo 'before';
        parent::__construct();
        echo 'I have made it after the parent constructor call';
    }

}

exit;
What could prevent me from calling the parent's constructor?
解决方案
SplQueue inherits from SplDoublyLinkedList. Neither of these classes defines a constructor of its own. Therefore there's no explicit parent constructor to call, and you get such an error. The documentation is a little misleading on this one (as it is for many SPL classes).

To solve the error, don't call the parent constructor.



Now, in most object-oriented languages, you'll expect the default constructor to be called if there isn't an explicit constructor declared in a class. But here's the catch: PHP classes don't have default constructors! A class has a constructor if and only if one is defined.

In fact, using reflection to analyze the stdClass class, we see even that lacks a constructor:
$c = new ReflectionClass('stdClass');
var_dump($c->getConstructor()); // NULL
Attempting to reflect the constructors of SplQueue and SplDoublyLinkedList both yield NULL as well.

My guess is that when you tell PHP to instantiate a class, it performs all the internal memory allocation it needs for the new object, then looks for a constructor definition and calls it only if a definition of __construct() or <class name>() is found. I went to take a look at the source code, and it seems that PHP just freaks out and dies when it can't find a constructor to call because you told it explicitly to in a subclass (see zend_vm_def.h).

                        
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