Access parent and child variables in method defined in parent - PHP

I have a child object that inherits from a parent. Both have a static variable which has a different value in each object; I want to add that variable from both parent and child to an array when I instantiate the child. To save duplicating code, I've written a method (addFoo) in the parent which is called from both the parent and the child constructors. However, I can't seem to find a way to distinguish between the calls when the parent constructor is called from the child constructor (as you can see below, the output from the method is the same in both cases whether using $this, self or static).

class A {
    public static $foo = 'foo';
    
    public $thisvars = array();
    public $selfvars = array();
    public $staticvars = array();
    
    public function __construct() {
        $this->addFoo();
    }
    
    public function addFoo() {
        $this->selfvars[] = self::$foo;
        $this->staticvars[] = static::$foo;
        $this->thisvars[] = $this::$foo;
    }
    
}

class B extends A {
    public static $foo = 'bar';
    
    public function __construct() {
        parent::__construct();
        $this->addFoo();
    }
}

$b = new B;
print_r($b->selfvars);
print_r($b->staticvars);
print_r($b->thisvars);

Output:

Array
(
    [0] => foo
    [1] => foo
)
Array
(
    [0] => bar
    [1] => bar
)
Array
(
    [0] => bar
    [1] => bar
)

I can workaround this by passing the calling class through to the addFoo function (see below), but is there a better (correct?) way?

class C {
    public static $foo = 'foo';
    
    public $vars = array();
    
    public function __construct() {
        $this->addFoo(__CLASS__);
    }
    
    public function addFoo($class) {
        $this->vars[] = $class::$foo;
    }
    
}

class D extends C {
    public static $foo = 'bar';
    
    public function __construct() {
        parent::__construct();
        $this->addFoo(__CLASS__);
    }
}

$d = new D;
print_r($d->vars);

Output:

Array
(
    [0] => foo
    [1] => bar
)

Demo on 3v4l.org

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