This is a quick demonstration to show how PHP classes can access other classes/sub-classes private properties.

private-property-access-2.php

<?php

class Doge
{

    private $name;

    public function __construct($name)
    {
        $this->name = $name;
    }

    public function getName()
    {
        return $this->name;
    }

    public function equalsWithSameType(self $other)
    {
        return ($other->name === $this->name);
    }

    public function equalsWithSubType(DogeCoin $sub)
    {
        return ($sub->name === $this->name);
    }

    public function equalsWithRandomType(SomethingElseCompletely $whatever_man)
    {
        return ($whatever_man->name === $this->name);
    }
}

class DogeCoin extends Doge
{
    private $name;
}

class SomethingElseCompletely
{
    private $name;

    public function __construct($name) {
        $this->name = $name;
    }
}

$first_doge = new Doge('a');
$second_doge = new Doge('a');
$doge_coin = new DogeCoin('a');
$something_else_completely = new SomethingElseCompletely('a');

var_dump($first_doge->equalsWithSameType($second_doge));
var_dump($first_doge->equalsWithSubType($doge_coin));
var_dump($first_doge->equalsWithRandomType($something_else_completely));