Nette Events

nette-events.php

<?php

class Circle
{
	public array $onChange = [];
	public float $radius = 0;

	public function setRadius(float $radius): void
	{
		foreach ($this->onChange as $handler) {
			$handler($this, $radius);
		}
		// alternatively: Nette\Utils\Arrays::invoke($this->onChange, $this, $radius);

		$this->radius = $radius;
	}
}

$circle = new Circle;

// add event handler
$circle->onChange[] = function (Circle $circle, float $newValue): void {
	echo 'change has occurred';
};

$circle->setRadius(10);