检查魔术设置的属性上是否存在属性

关于此主题有很多SO问题，特别是这个问题，但是它对我没有帮助.

There is a lot of SO questions about the subject, notably this one, but it does not help me.

property_exists和isset之间存在歧义，因此在提出问题之前，我先指出一下:

There is an ambiguity between property_exists and isset so before asking my question, I'm going to pointing it out:

property_exists 检查对象是否包含属性，而不查看其属性值，它只会查看其可见性.

property_exists checks if an object contains a property without looking at its value, it only looks at its visibility.

因此在以下示例中:

<?php

class testA
{
  private $a = null;
}
class testB extends testA
{
}

$test = new testA();
echo var_dump(property_exists($test, 'a')); // true

// parent's private property becomes invisible for its child

$test = new testB();
echo var_dump(property_exists($test, 'a')); // false

isset

isset 会检查属性中是否存在值，并考虑到如果值等于 false和 null，则不会设置.

isset

isset checks if a value exists in a property, considering that is is not set if a value equals false and null.

<?php

$var = null;
echo var_dump(isset($var)); // false

$var = '';
echo var_dump(isset($var)); // true

$var = false;
echo var_dump(isset($var)); // true

$var = 0;
echo var_dump(isset($var)); // true

$var = '0';
echo var_dump(isset($var)); // true

isset和property_exists在神奇添加的属性上的行为

一个属性可以带有一个null值，所以我不能使用__isset魔术方法来知道一个属性是否存在.我也不能使用property_exists，因为属性是使用魔术方法添加的.

isset and property_exists's behaviour on magically added properties

A property can exist with a null value, so I can't use __isset magic method to know if a property exist or not. I also can't use property_exists as properties are added using magic methods.

这里是一个示例，但这只是一个示例，因为在我的应用程序中，神奇设置的属性存储在对象外部.

Here is a sample, but this is just a sample because in my app, properties magically set are stored outside the object.

class test {

    private $data = array();

    public function __get($key) {
        echo "get $key\n";
        return array_key_exists($key, $data) ? $data[$key] : null;
    }

    public function __set($key, $value) {
        echo "set $key = $value\n";
        $this->data[$key] = $value;
    }

    public function __isset($key) {
       echo sprintf("isset $key ( returns %b )", isset($this->data[$key]));
       return isset($this->data[$key]);
    }

}

$test = new test();
$test->x = 42;
isset($test->x); // 1

$test->y = null;
isset($test->y); // 0
property_exists($test, 'y'); // 0

这是我的问题:

是否存在魔术方法或SPL接口来实现具有魔术添加属性的property_exist?