php参考 [英] Php By Reference

问题描述

有人可以解释一下&"是什么吗?执行以下操作:

Can someone please explain what the "&" does in the following:

class TEST {

}

$abc =& new TEST();

我知道这是参考.但是有人可以说明为什么以及何时需要这种东西吗?或将我指向一个网址，其中的解释很好.我无法理解这个概念.

I know it is by reference. But can someone illustrate why and when I would need such a thing? Or point me to a url where this is explained well. I am unable to grasp the concept.

非常感谢您.

推荐答案

据我了解，您并不是在问一般的PHP引用，而是关于$foo =& new Bar();构造习惯的问题.

As I understand it, you're not asking about PHP references in general, but about the $foo =& new Bar(); construction idiom.

这仅在PHP4中可见，因为通常的$foo = new Bar()存储对象的副本.除非类在构造函数中存储了对$ this的引用，否则通常不会注意到这一点.稍后在对返回的对象调用方法时，当意图可能只有一个时，将存在该对象的两个不同副本.

This is only seen in PHP4 as the usual $foo = new Bar() stores a copy of the object. This generally goes unnoticed unless the class stored a reference to $this in the constructor. When calling a method on the returned object later on, there would be two distinct copies of the object in existence when the intention was probably to have just one.

考虑以下代码，其中构造函数在全局var中存储对$ this的引用

Consider this code where the constructor stores a reference to $this in a global var

class Bar {
    function Bar(){
       $GLOBALS['copy']=&$this;
        $this->str="hello";
    }

}

//store copy of constructed object
$x=new Bar;
$x->str="goodbye";

echo $copy->str."\n"; //hello
echo $x->str."\n"; //goodbye

//store reference to constructed object
$x=&new Bar;
$x->str="au revoir";

echo $copy->str."\n"; //au revoir
echo $x->str."\n"; //au revoir

在第一个示例中，$ x和$ copy引用了Foo的不同实例，但是在第二个示例中，它们是相同的.

In the first example, $x and $copy refer to different instances of Foo, but in the second they are the same.

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