在PHP中可以反转遍历一个可遍历类来查找根对象？ [英] In PHP is it possible to reverse traverse a Traversable class to find the root object?

问题描述

如果要扩展一个实现Traversable的内置类，那么可以通过debug_backtrace获得对根对象的引用？

If one were to extend a built in class that implements Traversable would it be possible to obtain a reference to the root object perhaps with debug_backtrace?

例如，如果我有

$foo->bar->baz->biz->bon->bop->bob();

在bop的bob方法中我使用debug_backtrace有一种方法来获取$ foo的？ （那怎么样？）

and in the bob method of bop I make use of debug_backtrace is there a way to get a reference to $foo? (And what is that way?)

如果是这样，甚至是最优雅或最有效的方式呢？

If so is this even the most elegant or efficient way to do that?

我试过看看debug_backtrace php.net页面，我仍然不清楚如何真正使用这个功能，但从其他材料和实验我有我的疑虑（见更新）。

I've tried looking at the debug_backtrace php.net page and I am still not the clear how to really use this function but from other material and experimentation I have my doubts (see update).

更新＃1：

似乎有一些争论，如果debug_backtrace应该留在生产代码。 生产代码中的PHP debug_backtrace

There does seem to be some debate on if debug_backtrace should be left in production code. PHP debug_backtrace in production code?

当然，其中一部分是耦合的问题，一个被调用的对象是否知道对象调用它？

Of course part of this is the issue of coupling, should a called object have knowledge of the object calling it?

更新＃2

找到在另一个类中查找哪个类叫做一个方法？我尝试使用我学到的方法来使用debug_backtrace来反转遍历，并发现它不太可能。 p>

After finding Find out which class called a method in another class I tried my hand at using what I have learned to reverse traverse using debug_backtrace and discovered that it is not likely to be possible.

<?php

class mother extends SimpleXMLElement {

    protected $test_a = 'foo';
    public $test_b = 'bar';

    public function shout(){
        echo "test_a '" , $this->test_a , "' while test_b '" , $this->test_b , "'.\n";
    }

    public function tell_mother($message,$limit=42){    
        $trace = debug_backtrace();
        --$limit;
        if($limit<1){
            echo "Enough of that pointlessness\n";
            var_dump($trace);
            return 0;
        }
        if ( isset($trace[1]) && isset($trace[1]['object']) ){
            // $trace[1] is the caller class
            echo "I will pass the message on\n";
            $trace[1]['object']->tell_mother($message,$limit);
        }else{
            echo "I am a " , get_class($this) , "\n";
            echo "I have been told \"{$message}\".\n";
            var_dump($trace);
        }
    }


}

echo "<pre>";

$xml = <<<XML
<?xml version='1.0'?> 
<a>lob
    <b>tob
        <c>bob
            <d>boo
                <e>bin
                    <f>baz
                        <g>bar
                            <h>foo</h>
                        </g>
                    </f>
                </e>
            </d>
        </c>
    </b>
</a>

XML;

$obj = simplexml_load_string($xml,'mother');
$obj->b->c->d->e->f->g->h->tell_mother("I love her");
$obj->shout();
$obj->b->c->d->e->f->shout();

据我所知，debug_backtrace不能反转遍历，也不能访问对象范围中保留的值。

As far as I can tell debug_backtrace cannot reverse traverse and no values held in object scope can be accessed.

上面的输出给了

I am a mother
I have been told "I love her".
array(1) {
  [0]=>
  array(7) {
    ["file"]=>
    string(58) "/home/[[snip]]_test.php"
    ["line"]=>
    int(64)
    ["function"]=>
    string(11) "tell_mother"
    ["class"]=>
    string(6) "mother"
    ["object"]=>
    object(mother)#2 (1) {
      [0]=>
      string(3) "foo"
    }
    ["type"]=>
    string(2) "->"
    ["args"]=>
    array(1) {
      [0]=>
      &string(10) "I love her"
    }
  }
}
test_a '' while test_b ''.
test_a '' while test_b ''.

我的结论是，PHP内部看不到父元素调用的子元素。所以我已经编辑了我的问题，只要问是否可以反转遍历一个可遍历的类。

My conclusion is that internally PHP does not see the child elements as being called by the parents. So I have edited my question to simply ask if it is possible to reverse traverse a Traversable class.

推荐答案

通过跟踪和错误（主要是错误），我在这个问题中详细介绍了至少有一些PHP类实现可扩展只显示为类，但实际上是系统资源。

Through trail and error (mostly error) which is detailed in the question I have learned that at least some PHP classes which implement Traversable only appear to be classes but are actually system resources.

所以debug_backtrace（我的第一个想法）将无法反转遍历。很可能这是不可能的，但有一点创造性，可以创建一个委托包装器来提供实际对象的双向遍历。

So debug_backtrace (my first idea) will not be able to to reverse the traversal. It is likely that this is not possible but with a little ingenuity a delegation wrapper can be created to provide two way traversing of actual objects.

一个这样的类的例子可以在我对另一个问题的答复中找到：如何获取PHP中根对象的迭代对象引用？

An example of one such class can be found in my answer to another question I asked: How do I obtain an iterative object reference to the root object in PHP?

此外，debug_backtrace不是

Furthermore debug_backtrace is not a great choice for doing anything in production beyond error logging and debugging for which it was designed.

TD; DR：可能不是，但我们可以解决这个问题。

TD;DR : Probably not, but we can fix that.

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