在PHP中测试变量存在的最佳方法; isset()显然已被打破

// 测试数组中的键是否存在
$array = ['key1' => 'value1', 'key2' => null];
if (array_key_exists('key1', $array)) {
    echo "Key1 exists\n";
}
if (!array_key_exists('key2', $array)) {
    echo "Key2 does not exist\n";
}

// 测试对象中的属性是否存在
class MyClass {
    public $property1 = 'value1';
    public $property2;
}

$obj = new MyClass();
if (property_exists($obj, 'property1')) {
    echo "Property1 exists\n";
}
if (!property_exists($obj, 'property2')) {
    echo "Property2 does not exist\n";
}