Events.php

class Event {
  public $things;
  
  public function __construct($things) { $this->things = $things; }
}

class Event_v2 {
  public $things;
  public $anotherThing;
  
  static public function fromEvent(Event $e) { return new Event_v2($e->things, 'no other thing here at this point bro'); }

  public function __construct($things, $anotherThing) { ... }
}