Referring to a PHP superclass name via a magic constant / keyword or similar construct (avoiding naming the superclass in the derived class)

Question

The comments in the following code show what I am trying to accomplish, which is something very simple: I want to be able to refer to the name of the parent class using a PHP built-in constant (or other construct) such as __CLASS__, but which refers to the parent class rather than the current class (e.g. parent::__CLASS__) (also, while the code does not show it, if I have a subsubclass, then within such class I want to be able to refer t the parent class via something like parent::parent::__CLASS__ if at all possible).

class ParentClass {

  protected $foo;

  function __construct() {

    $this->foo = "hello";

  }

}

class DerivedClass extends ParentClass {

  public $bar;

  public $baz;

  function __construct($bar) {

    // I want to be able to write
    // something like parent:__CLASS__
    // here in place of 'ParentClass'
    // so that no matter what I rename
    // the parent class, this line will
    // always work. Is this possible?

//      if (is_a($bar, parent::__CLASS__)) {

    if (is_a($bar, 'ParentClass')) {

      $this->bar = $bar;

    } else {

      die("Unexpected.");

    }

    $this->baz = "world";

  }

  public function greet() {

    return $this->bar->foo . " " . $this->baz;

  }

}

$d = new DerivedClass(new ParentClass());
echo $d->greet();

OUTPUT:

hello world

Answer 1

You need get_parent_class Function to do it.

function __construct($bar) {

    $parent = get_parent_class($this);


    if (is_a($bar, $parent)) {

      $this->bar = $bar;

    } else {

      die("Unexpected.");

    }

    $this->baz = "world";

  }

if you need further level down you can use:

class subDerivedClass extents DerivedClass{
    $superParent = get_parent_class(get_parent_class($this));
}

Answer 2

In PHP 5.5, you can use the keyword ::class to retrieve the name of a class' parent, but it will only work a) from within the class and b) only one level up, that is the immediate parent ancestor:

function __construct($bar) {
   if ($bar instanceof parent::class) {
      ...
   }
}

Best solution I'd go for is chaining get_parent_class:

if ($bar instanceof get_parent_class(get_parent_class())) {
    ...
}

Or method chaining through reflection:

$parent_class = (new Reflection($this))->getParentClass()->getParentClass()->getName();

if ($bar instanceof $parent_class) {
    ...
}