PHP 5 : return by ref method produces unexpected results

我创建了一个简单的类来管理一个行为异常的树数据结构(代码如下)。当很明显这不是我的错误时，我创建了一个测试用例，它产生了同样令人费解的行为。这在 5.3 和 5.4 中是相同的。

这是我的测试用例:

<?php
class testcaseA {
    public function __construct($one=0, $two=1, $three=2) {
        $this->obj = new testcaseB($one++, $three, $two);
    }
    public function &get($what){
        return $this->obj->get($what);
    } 
}
class testcaseB {
    public function __construct($one, &$two, &$three) {
        $this->one=$one;
        $this->two=$two;
        $this->three=$three;
        echo "\$one={$one}";
    }
    public function &get($what){
        echo "<p>You asked for $what. $what ain't no country I ever heard of.<br />";
        echo "Check: [{$this->one}], {$this->two}, {$this->three}. Is this thing on?</p>";
        $this->obj[$what] = new testcaseB($this->one++,$this->two,$this->three);
        return $this->obj[$what];
    } 
}
ini_set('display_errors',1); 
error_reporting(E_ALL);
$bob = new testcaseA();
$bob->get("What")->get("Spam")->get("America");
$bob->get("What")->get("EU")->get("France");
echo "<pre>";
print_r($bob);

现在我期望的输出是看到 $one 增量 1,2,3,1,2,3 的值并生成树形。

这是我实际得到的输出:

$one=0

You asked for What. What ain't no country I ever heard of.
Check: [0], 2, 1. Is this thing on?
$one=0

You asked for Spam. Spam ain't no country I ever heard of.
Check: [0], 2, 1. Is this thing on?
$one=0

You asked for America. America ain't no country I ever heard of.
Check: [0], 2, 1. Is this thing on?
$one=0

You asked for What. What ain't no country I ever heard of.
Check: [1], 2, 1. Is this thing on?
$one=1

You asked for EU. EU ain't no country I ever heard of.
Check: [1], 2, 1. Is this thing on?
$one=1

You asked for France. France ain't no country I ever heard of.
Check: [1], 2, 1. Is this thing on?
$one=1

testcaseA Object
(
    [obj] => testcaseB Object
        (
            [one] => 2
            [two] => 2
            [three] => 1
            [obj] => Array
                (
                    [What] => testcaseB Object
                        (
                            [one] => 2
                            [two] => 2
                            [three] => 1
                            [obj] => Array
                                (
                                    [EU] => testcaseB Object
                                        (
                                            [one] => 2
                                            [two] => 2
                                            [three] => 1
                                            [obj] => Array
                                                (
                                                    [France] => testcaseB Object
                                                        (
                                                            [one] => 1
                                                            [two] => 2
                                                            [three] => 1
                                                        )

                                                )

                                        )

                                )

                        )

                )

        )

)

起初这让我感到困惑，但我想知道是否链接使用以我没有预料到的方式设置值。

所以我尝试了这个我在之前的代码之后添加的代码:

...same classes and initial code as before...
$a=$bob->get("What");
$b=$a->get("Spam");
$c=$b->get("America");
//$bob->get("What")
$d=$a->get("EU");
$e=$d->get("France");  
print_r($bob);

这产生了一组不同但仍然不可预测的结果。

You asked for What. What ain't no country I ever heard of.
Check: [2], 2, 1. Is this thing on?
$one=2

You asked for Spam. Spam ain't no country I ever heard of.
Check: [2], 2, 1. Is this thing on?
$one=2

You asked for America. America ain't no country I ever heard of.
Check: [2], 2, 1. Is this thing on?
$one=2

You asked for EU. EU ain't no country I ever heard of.
Check: [3], 2, 1. Is this thing on?
$one=3

You asked for France. France ain't no country I ever heard of.
Check: [3], 2, 1. Is this thing on?
$one=3testcaseA Object
(
    [obj] => testcaseB Object
        (
            [one] => 3
            [two] => 2
            [three] => 1
            [obj] => Array
                (
                    [What] => testcaseB Object
                        (
                            [one] => 4
                            [two] => 2
                            [three] => 1
                            [obj] => Array
                                (
                                    [Spam] => testcaseB Object
                                        (
                                            [one] => 3
                                            [two] => 2
                                            [three] => 1
                                            [obj] => Array
                                                (
                                                    [America] => testcaseB Object
                                                        (
                                                            [one] => 2
                                                            [two] => 2
                                                            [three] => 1
                                                        )

                                                )

                                        )

                                    [EU] => testcaseB Object
                                        (
                                            [one] => 4
                                            [two] => 2
                                            [three] => 1
                                            [obj] => Array
                                                (
                                                    [France] => testcaseB Object
                                                        (
                                                            [one] => 3
                                                            [two] => 2
                                                            [three] => 1
                                                        )

                                                )

                                        )

                                )

                        )

                )

        )

)

这仍然不是我所追求的行为，但它更接近。我需要的是使用一个对象链来遍历树(与第一种情况一样)，一个指向值 $two 和 $three 的指针，在实际情况下它们是数组而不是交换。我不想做的是不必要地复制对象。

另一方面，我确实需要让所有对象共享一对它们都使用的变量。

我的猜测是 get() 方法可以是 byval 而不是 byref 尽管直觉上这似乎是错误的。

谁能解释一下 $one 值的作用？

还有谁能帮我理解第一个测试用例的行为，尤其是第一次对数组中的值的理解？

更新

利用这些很棒的建议，我们的测试用例现在看起来像:

class testcaseA {
    public function __construct($one=0, $two=1, $three=2) {
        $this->obj = new testcaseB(++$one, $three, $two);
    }
    public function &get($what){
        return $this->obj->get($what);
    } 
}
class testcaseB {
    public function __construct($one, &$two, &$three) {
        $this->one=$one;
        $this->two=$two;
        $this->three=$three;
        echo "[New:\$one={$one}]:";
    }
    //public function &get($what){
    public function &get($what){
        //echo "<p>You asked for $what. $what ain't no country I ever heard of.<br />";
        echo "Get:{$what}:[{$this->one}]<br />";
        if(!isset($this->obj[$what])){
            $this->obj[$what] = new testcaseB(++$this->one,$this->two,$this->three);
        }
        return $this->obj[$what];
    } 
}
echo "STARTING:<br />";
ini_set('display_errors',1); 
error_reporting(E_ALL);
echo "REALLY STARTING:<br />";
echo "<pre>";
echo "<p>One at a time:</p>";
$bob = new testcaseA();
$a=$bob->get("What");
$b=$a->get("Spam");
$c=$b->get("America");
$d=$a->get("EU");
$e=$d->get("France"); 
echo "<br />";
print_r($bob); 
echo "<p>Chained:</p>";
$bobby = new testcaseA();
$bobby->get("What")->get("Spam")->get("America");
$bobby->get("What")->get("EU")->get("France");
echo "<br />";
print_r($bob);

其中的输出是:

输出数字似乎正确，但 $one 不在堆栈中。

最佳答案

如果我理解您的疑惑(我认为我理解)，您就会遇到 pre- and post-increment 之间的细微差别。 .这可以最容易地在代码中演示:

$a = 1;
echo $a++; // 1
echo $a;   // 2

另一方面:

$a = 1;
echo ++$a; // 2
echo $a;   // 2

基本上，通过将 ++ 放在您增加的值之前，您将获得新值。通过将它放在后面(正如您所做的那样)，您将获得旧值。

我认为您代码中的关键行是:

$this->obj[$what] = new testcaseB($this->one++,$this->two,$this->three);

...应该是这样的:

$this->obj[$what] = new testcaseB(++$this->one,$this->two,$this->three);

随着后递增，$this->one 的初始值将被带入所有后续迭代。

附带说明一下，我认为您不必担心此处通过引用返回，因为无论如何 PHP5 中的所有对象都是通过引用传递的。

关于PHP 5 : return by ref method produces unexpected results，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/11313294/

PHP 5 : return by ref method produces unexpected results

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