Description:
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It'll be very useful to add the ability to cast an object to a parent class.
A simple example could be security: having a base class with attributes, is extended by another that can do CRUD operations on DB. When passing to VIEW layer (according to MVC), just do a cast to base object, and CRUD actions will be disabled.

Reproduce code:
---------------
class Person {
  protected $age;
  function getAge() { return $this->age; }
  function setAge($age) {$this->age = $age; }
}

class PersonDB extends person {
  function load($id) {
    // SQL execution
    $this->setAge($resultSet->age);
  }
}

in Model layer:
$objPersonDB = new PersonDB();
$objPersonDB->load($id);

in Controller layer, sends $person to View layer:
$person = (Person)$objPersonDB;

Expected result:
----------------
if I call, in View layer:
$person->load(5);
must raise an error

Actual result:
--------------
cast do nothing, method is invoked.